Comparative study of thyroid function and types of thyroid dysfunction in two areas in Denmark with slightly different iodine status

[Regional Differences in Thyroid Function Parameters: A Comparison of European Cohort Studies]

AIM OF THE STUDY

The aim of the project was to investigate regional differences in thyroid stimulating hormone (TSH), and free thyroxine (fT4) concentrations and iodine status in comparable German and European cohort studies.

METHODS

Sex- and age-stratified TSH, fT4, and urine iodine concentrations of thyroid-healthy participants (age group 45-75 years) of the HNR (Heinz Nixdorf Recall) Study in the Ruhr region of Germany, the southern German KORA (Cooperative Health Research in the Augsburg Region) and northeastern German SHIP (Study of Health in Pomerania) studies, as well as the Norwegian HUNT (Nord-Trøndelag Health) study (age group 40-79 years), the English EPIC (European Prospective Investigation of Cancer)-Norfolk study, and the Dutch Rotterdam study were compared. The TSH reference range for the HNR study population was calculated and compared to the KORA and SHIP studies.

RESULTS

Regional differences showed a stronger influence on TSH and fT4 concentrations than sex and age of the subjects in the 45- to 75-year age group. The estimated difference in medians, as measured by the HNR study, was lowest in the SHIP study, -0.47 (95% CI: -0.53; -0.41) for men and -0.41 (-0.53; -0.41) for women. The Rotterdam study had the highest difference in medians for both men and women (men: 0.56 with 0.44; 0.68 and women: 0.62 with 0.46; 0.78). The lowest median TSH concentrations, across all age categories considered, were seen in the German cohorts.

CONCLUSIONS

Comparison of thyroid function parameters and iodine in elderly subjects between six comparable cohort studies from Germany and Europe showed a significant influence of region, which exceeded the sex and age dependence of the parameters.

The management and metabolic characterization: hyperthyroidism and hypothyroidism

Hyperthyroidism and hypothyroidism are common diseases resulting from thyroid dysfunction, and are simple to diagnose and treat. The traditional treatment for hypothyroidism is thyroid hormone replacement therapy. The traditional treatments for hyperthyroidism include antithyroid drug, iodine radiotherapy, and surgery. Thyroid disease can be fatal in severe cases if untreated. Current statistical reference ranges used for diagnosis based on relevant biochemical parameters have been debated, and insufficient treatment can result in long-term thyroid hormone deficiency, which is associated with increased risk of cardiovascular disease and persistent symptoms. In contrast, overtreatment can result in heart disease and osteoporosis, particularly in older people and pregnant women. Therefore, under- or over-treatment should be avoided and treatment regimens should be monitored closely. A significant proportion of patients who achieve biochemical treatment goals still complain of significant symptoms. Systematic literature review was performed through the Embase (Elsevier), PubMed and Web of Science databases, and studies summarized evidence regarding treatment and management of hypothyroidism and hyperthyroidism, and reviewed clinical practice guidelines. We also reviewed the latest research on the metabolic mechanisms of hyperthyroidism and hypothyroidism, which contributed to understanding of thyroid diseases in the clinic. A reliable algorithm is needed to management, assessment, and treatment patients with hyperthyroidism and hypothyroidism, which can not only improve management efficiency, but also providing a broad application. In addition, the thyroid disorder showed a lipid metabolism tissue specificity in the Ventromedial Hypothalamus, and effect oxidative stress and energy metabolism of whole body. This review summarizes an algorithm for thyroid disease and the latest pathogenesis that would be useful to generalist and subspecialty physicians and others providing care for patients with this condition.

Iodine Deficiency in Patients with Hypothyroidism: A Pilot Study

Objective

Worldwide, 21 countries have insufficient iodine in their diets. Persistent iodine deficiency may result in hypothyroidism. The aim of this study is to determine whether iodine measurements can be used to determine the prevalence of iodine deficiency in patients with (subclinical) hypothyroidism compared to a control group.

Design

A prospective cohort pilot study was performed at the Internal Medicine Outpatient Clinic of Isala, a large teaching hospital in Zwolle, the Netherlands. Patients. This study consisted of two groups of 24 adult patients each: a group of consecutive patients presenting with overt or subclinical hypothyroidism and a control group of euthyroid patients with type 1 diabetes mellitus. Measurements. All patients collected 24-hour urine. Iodine status was determined using urinary iodine concentration (UIC), urinary iodine excretion (UIE), and iodine creatinine ratio (I : Cr). Iodine deficiency was defined as an iodine concentration <100 µg/L for UIC, iodine level <125 µg for UIE, and <0.13 µmol/mmol for I : Cr.

Results

According to UIE and UIC measurements, 54.2% of hypothyroid patients were iodine-deficient compared to 41.7–45.8% in the control group. According to the I : Cr measurement 91.7% of hypothyroid patients were iodine-deficient compared to 87.5% in the control group. No significant difference was seen between the two groups. No correlation was found between thyroid-stimulating hormone (TSH) level and iodine deficiency.

Conclusions

Iodine deficiency is prevalent in both hypothyroid patients and euthyroid patients. Because there is no significant difference between the groups, a single 24-hour urine or spot urine sample to determine UIC, UIE, and I : Cr, seems not suitable to determine iodine status in an individual participant.

Thyroid autoimmunity in Greenlandic Inuit

Objective

This study aimed to provide the first data on the occurrence of thyroid autoimmunity among Inuit in Greenland, a distinct ethnic group who is not iodine deficient.

Design

This study is a population-based cross-sectional study.

Methods

Data were collected in Nuuk in West Greenland and in Ammassalik district in East Greenland. Information on lifestyle, diet and diseases was obtained using questionnaires. Thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TGAb) and thyroid-stimulating hormone (TSH) were measured in serum. Iodine and creatinine were measured in spot urine samples.

Results

The participation rate was 95% with 434 Inuit participants; 75% were smokers. Iodine excretion was 169 µg/24 h in urban West Greenland, 224 µg/24 h in the main town and 228 µg/24 h in settlements in rural East Greenland. TPOAb, TgAb or either of these was measured in the serum from 3.7, 5.9 and 8.3% of participants, respectively. TPOAb or TgAb was found in 9.3% of Inuit women and 7.5% of men and more frequently, in East Greenland Inuit with the higher iodine excretion (P = 0.02). There was some evidence suggesting that thyroid autoimmunity was more frequent among non-smokers (12.5%) compared to smokers (7.0%). Harbouring a thyroid autoantibody was most frequent in participants with TSH above 3.6 mIU/L (P < 0.001).

Conclusion

Thyroid autoantibodies were rare among Greenland Inuit. While iodine nutrition was associated with autoimmunity similarly to other ethnic groups, the influence of sex and smoking was limited. This could suggest genetic component in Inuit, but the impact of cold, selenium and persistent organic pollutants needs to be elucidated.

The Impact of Iodine Concentration Disorders on Health and Cancer

Iodine deficiency is an ongoing problem. The implementation of salt iodization has significantly reduced the effects of iodine deficiency worldwide in recent years, and the remaining iodine deficiency is mild to moderate. Iodine is an essential substrate for the synthesis of thyroid hormones in the thyroid gland. It can also act as an antioxidant, as well as an anti-proliferative and pro-apoptotic factor. Pregnant women, breastfeeding women, and children are particularly affected by iodine deficiency. It leads to thyroid diseases and metabolic and developmental disorders, as well as cancer. However, an excessive iodine intake may, similarly to iodine deficiency, lead to the development of goiter, and toxic amounts of iodine can lead to thyroiditis, hyperthyroidism, and hypothyroidism, and even to the development of papillary thyroid cancer. Correcting iodine deficiency potentially reduces the chance of developing malignancies. Additional research is needed to better understand both the effect of iodine on carcinogenesis and the clinical outcome of iodine deficiency compensation on cancer patients' prognosis. The upcoming public health challenge appears to be reducing salt consumption, which could result in a lower iodine intake. Thus, an iodine enrichment vehicle other than salt could be considered if salt iodine levels are not increased to compensate, and urine iodine levels should be monitored more frequently.

Thyroid Function across the Lifespan: Do Age-Related Changes Matter?

Circulating concentrations of thyrotropin (TSH) and thyroxine (T4) are tightly regulated. Each individual has setpoints for TSH and free T4 which are genetically determined, and subject to environmental and epigenetic influence. Pituitary-thyroid axis setpoints are probably established in utero, with maturation of thyroid function continuing until late gestation. From neonatal life (characterized by a surge of TSH and T4 secretion) through childhood and adolescence (when free triiodothyronine levels are higher than in adults), thyroid function tests display complex, dynamic patterns which are sexually dimorphic. In later life, TSH increases with age in healthy older adults without an accompanying fall in free T4, indicating alteration in TSH setpoint. In view of this, and evidence that mild subclinical hypothyroidism in older people has no health impact, a strong case can be made for implementation of age-related TSH reference ranges in adults, as is routine in children.

Assessment of iodine fortification of salt in the Danish population

PURPOSE

We assessed the effect of the current iodine fortification level (20 µg/g household salt and salt included in bread and bakery products) on inadequate and excessive intake in the general Danish population. Intake models with/without the contribution from food supplements and effects of excluding specific food groups were evaluated.

METHOD

Data from the Danish National Survey of Dietary Habits and Physical Activity in 2011-13 (N = 3946, aged 4-75 years) stratified by age-group and sex were used to estimate habitual dietary iodine intakes, and compared with established dietary reference values.

RESULTS

The proportion with an estimated inadequate iodine intake was ≤ 3% for males and ≤ 5% for females, except for 15-17-year-old girls, where the probable prevalence of an inadequate intake was 11%. Including the contribution from food supplements gave similar results (10%). High intakes (as defined by 95th percentile) from food sources generally did not exceed the tolerable upper intake level (UL). However, for the youngest age-groups (4-6-year-old boys/girls and 7-10-year-old boys), the 95th percentiles exceeded the UL with 11%, 4% and 7%, respectively, when food supplements were included in the estimates. Especially exclusion of dairy products and bread led to an inadequate intake for both boys and girls.

CONCLUSION

The current fortification level may provide an inadequate iodine intake for some females and on the other hand lead to excessive intakes in the youngest age-groups. The study shows the importance of choosing iodine-rich alternatives when excluding major sources of iodine in the Danish diet.

The pattern of TSH and fT4 levels across different BMI ranges in a large cohort of euthyroid patients with obesity

PURPOSE

A multifold association relates the hypothalamo-pituitary-thyroid axis to body weight. The potential underlying mechanisms are incompletely understood. Further, the mild severity of obesity and the small proportion of individuals with obesity in so far published cohort studies provide little insights on metabolic correlates of thyroid function in obesity.

METHODS

We retrospectively enrolled 5009 adults with obesity (F/M, 3448/1561; age range, 18-87 years; BMI range, 30.0-82.7 kg/m²), without known thyroid disease in a study on TSH and fT4 levels, lipid profile, glucose homeostasis and insulin resistance, anthropometric parameters including BIA-derived fat mass (%FM) and fat-free mass (FFM).

RESULTS

The overall reference interval for TSH in our obese cohort was 0.58-5.07 mIU/L. As subgroups, females and non-smokers showed higher TSH levels as compared to their counterparts (p<0.0001 for both), while fT4 values were comparable between groups. There was a significant upward trend for TSH levels across incremental BMI classes in females, while the opposite trend was seen for fT4 levels in males (p<0.0001 for both). Expectedly, TSH was associated with %FM and FFM (p<0,0001 for both). TSH and fT4 showed correlations with several metabolic variables, and both declined with aging (TSH, p<0.0001; fT4, p<0.01). In a subgroup undergoing leptin measurement, leptin levels were positively associated with TSH levels (p<0.01). At the multivariable regression analysis, in the group as a whole, smoking habit emerged as the main independent predictor of TSH (β=-0.24, p<0.0001) and fT4 (β=-0.25, p<0.0001) levels. In non-smokers, %FM (β=0.08, p<0.0001) and age (β=-0.05, p<0.001) were the main significant predictors of TSH levels. In the subset of nonsmokers having leptin measured, leptin emerged as the strongest predictor of TSH levels (β=0.17, p<0.01).

CONCLUSIONS

Our study provides evidence of a gender- and smoking-dependent regulation of TSH levels in obesity.

Adaptation to a High Iodine Intake in Greenland Inuit Suggested by Thyroid Disease Pattern

Objective: Arctic living is influenced by cold winters, short summers, and excessive iodine intake from the traditional Inuit diet providing for habitation of the Arctic for centuries. This is changing and we surveyed thyroid function in populations living in Greenland. Design: Population-based cross-sectional study. Methods: Data were collected in the capital city in West Greenland and in rural East Greenland. Information on lifestyle, dietary habits, and medical history was obtained using questionnaires. Thyrotropin, free thyroxine, free triiodothyronine, thyroglobulin, and thyroglobulin antibody were measured in serum, iodine, and creatinine in spot urine samples. Results: One percent of the Greenlandic population was invited and 535 participated with an overall participation rate of 95%. Iodine excretion was 225 μg/24 hours in East Greenland and 169 μg/24 hours among West Greenland Inuit. Hyperthyroidism occurred in 10.7% of West Greenlandic Inuit (men/women: 4.3%/16.3%) and 7.8% of East Greenlandic Inuit (3.8%/12.8%). Hypothyroidism was found in 2.7% in West Greenland (0.0%/5.0%) and 5.6% (5.6%/5.6%) in East Greenland. Conclusion: Hyperthyroidism was frequent among Inuit and the occurrence of hypothyroidism was low. The pattern of hyper- and hypothyroidism among Greenlandic Inuit with adequate iodine intake was comparable with those seen in populations with iodine deficiency. Inuit may thus have adapted to excessive iodine intake over centuries, causing a need for a higher iodine intake to prevent iodine deficiency disorders.

Does Subclinical Hypothyroidism Add Any Symptoms? Evidence from a Danish Population-Based Study

BACKGROUND

Few studies have scrutinized the spectrum of symptoms in subclinical hypothyroidism.

METHODS

From 3 Danish Investigation on Iodine Intake and Thyroid Diseases (DanThyr) cross-sectional surveys performed in the period 1997 to 2005, a total of 8903 subjects participated in a comprehensive investigation including blood samples and questionnaires on previous diseases, smoking habits, alcohol intake, and education. From the 3 surveys we included patients with subclinical hypothyroidism (n = 376) and euthyroid controls (n = 7619). We explored to what extent patients with subclinical hypothyroidism reported 13 previously identified hypothyroidism-associated symptoms (tiredness, dry skin, mood lability, constipation, palpitations, restlessness, shortness of breath, wheezing, globus sensation, difficulty swallowing, hair loss, dizziness/vertigo, and anterior neck pain). In various uni- and multivariate regression models we searched for circumstances predicting why some patients have more complaints than others.

RESULTS

Subclinically hypothyroid patients did not report higher hypothyroidism score [(median, interquartile range), 2 (0-4) vs 2 (0-4), P = .25] compared with euthyroid controls. Within the group of subclinical hypothyroid patients, comorbidity had the highest impact on symptoms (tiredness, shortness of breath, wheezing; all P < .001); TSH level had no impact on symptom score; and younger age was accompanied by higher mental burden (tiredness, P < .001; mood lability, P < .001; restlessness, P = .012), whereas shortness of breath was associated with high body mass index (P < .001) and smoking (P = .007).

CONCLUSION

Patients with a thyroid function test suggesting subclinical hypothyroidism do not experience thyroid disease-related symptoms more often than euthyroid subjects. In subclinical hypothyroidism, clinicians should focus on concomitant diseases rather than expecting symptomatic relief following levothyroxine substitution.

Factors influencing the reference interval of thyroid-stimulating hormone in healthy adults: A systematic review and meta-analysis

BACKGROUND

Many studies have reported that the thyroid-stimulating hormone (TSH) reference interval is susceptible to external factors, such as age, sex, race, region and iodine intake. However, no meta-analysis has comprehensively explored the effect of these factors on the TSH reference interval.

METHODS

Articles published from January 1960 to January 2020 were searched in PubMed, Embase, Cochrane, Scopus, Medline English databases and CNKI, WanFang and CQVIP Chinese databases. In total, 19 studies were ultimately included. All data were analysed using Review Manager 5.3, STATA 16.0 software, GraphPad Prism 8.0 and Microsoft Excel 2010 to draw the TSH concentration curve.

RESULTS

The TSH reference interval was significantly influenced by sex and age. The mean of TSH concentration in females was 0.27 mIU/L higher than that in males. Reference interval of TSH is divided into 20-59 years old and >60 years old age groups in males, and 20-39 years old and >40 years old age groups in females. Regardless of sex, TSH concentrations all increase with age. In iodine-deficient areas, TSH reference intervals were generally lower than those in iodine-sufficient or iodine-excessive areas. The TSH reference interval in Asia and North American countries was generally higher than that in most European countries. In the subgroup analyses of sample size, region and assay methods and manufacturers, the between-group differences were significant.

CONCLUSION

The TSH reference interval was significantly influenced by sex, age, iodine intake, sample size, region, and assay methods and manufacturers, but other factors should not be ignored. Therefore, it is necessary for each laboratory to validate an appropriate TSH reference interval based on local conditions.

Hypothyrosis syndrome: role of triodthyronine in diagnostics and combination therapy (review of literature)

Hypothyroidism syndrome is one of the most common pathologies of the endocrine system. Assessment of euthyroid status can not always be carried out according to the TSH indicator. In a number of patients with normal TSH levels and a clinical picture of hypothyroidism, the serum T3 concentration is determined at the lower limit of the norm or below it with a high content of free T4 in the blood. In world practice, positive experience has been accumulated in the combined use of preparations of sodium levothyroxine and liothyronine, a synthetic form of exogenous triiodothyronine. A number of studies have noted the advantages of using combination therapy for hypothyroidism over levothyroxine monotherapy in certain groups of patients. Possible reasons for the ineffectiveness of standard treatment for hypothyroidism are described.

The role of laboratory medicine in the diagnosis of the hyperthyroidism

Hyperthyroidism is a clinical condition characterized by inappropriately high synthesis and secretion of thyroid hormones by the thyroid gland. It has multiple aetiologies, manifestations and potential therapies. Graves' disease is the most common form of hyperthyroidism, due to the production of autoantibodies against thyrotropin receptor, capable of over-stimulating thyroid function. A reliable diagnosis of hyperthyroidism can be established on clinical grounds, followed by the evaluation of serum thyroid function tests (thyrotropin first and then free thyroxine, adding the measurement of free triiodothyronine in selected specific situations). The recent guidelines of both the American and European Thyroid Associations have strongly recommended the measurement of thyrotropin receptor autoantibodies for the accurate diagnosis and management of Graves' disease. If autoantibody test is negative, a radioiodine uptake should be performed. Considering the most recent laboratory improvements, binding assays can be considered the best first solution for the measurement of thyrotropin receptor autoantibodies in diagnosis and management of overt cases of Graves' disease. In fact, they have a satisfactory clinical sensitivity and specificity (97.4% and 99.2%, respectively) being performed in clinical laboratories on automated platforms together with the other thyroid function tests. In this setting, the bioassays should be reserved for fine and complex diagnoses and for particular clinical conditions where it is essential to document the transition from stimulating to blocking activity or vice versa (e.g. pregnancy and post-partum, related thyroid eye disease, Hashimoto's thyroiditis with extrathyroidal manifestations, unusual cases after LT4 therapy for hypothyroidism or after antithyroid drug treatment for Graves' disease). Undoubtedly, technological advances will help improve laboratory diagnostics of hyperthyroidism. Nevertheless, despite future progress, the dialogue between clinicians and laboratory will continue to be crucial for an adequate knowledge and interpretation of the laboratory tests and, therefore, for an accurate diagnosis and correct management of the patient.

[The thyroid gland in old age : Physiology and pathology]

In healthy older people the metabolism of thyroid hormones is physiologically altered and can possibly even actively contribute to longevity. This should also be taken into consideration in the treatment of diseases of the thyroid and principally also for younger patients. For example, with progressing age comorbidities become more prevalent and especially in cardiovascular diseases, hyperthyroidism is less well tolerated, and should be treated more aggressively. Benign multinodular goiter also becomes more prevalent in old age and should be surgically treated when causing mechanical symptoms. The treatment concept for malignant diseases should be adapted to the holistic situation of the patient but principally in the same manner as in younger patients. Old and very old patients also benefit from adequate, risk-adapted treatment of thyroid gland diseases so that appropriate diagnostics and clarification are meaningful, regardless of age.

Prevalence of thyroid autoimmunity and effect of levothyroxine treatment in a cohort of 1064 patients with recurrent pregnancy loss

RESEARCH QUESTION

Does initiating levothyroxine treatment based on thyroid-stimulating hormone (TSH) >2.5 mIU/l or thyroid autoimmunity improve pregnancy continuation rates in recurrent pregnancy loss (RPL) patients?

DESIGN

A retrospective cohort study of 1064 RPL patients, in which subjects were classified as either euthyroid (TSH 0.1 to ≤2.5 mIU/l), borderline-subclinical hypothyroid (borderline-SCH, TSH 2.5 to ≤4 mIU/l) or subclinical hypothyroid (SCH, TSH 4 to ≤10 mIU/l). For subjects with ≥2 pregnancy losses and a subsequent pregnancy with known outcome, a comparison was done of the pregnancy continuation rate past 10 weeks of treated and untreated borderline-SCH (n = 98) and untreated euthyroid (n = 279) subjects, and between subjects with positive (n = 18) and negative (n = 206) thyroid peroxidase (TPOAb tests) within the borderline-SCH and euthyroid groups.

RESULTS

72.7% were euthyroid (721/992), 19.4% (192/992) were borderline-SCH, and 5.4% (54/992) were subclinically hypothyroid (SCH). Of 401 women with a subsequent pregnancy of known outcome at 10 gestational weeks, 21% received treatment with levothyroxine. 57.7% of subjects had a TPOAb test, which was positive in 9.25% (37/400) in euthyroid, 16.5% (22/133) in borderline-SCH subjects and 35.3% (12/34) in SCH subjects. Treatment did not improve pregnancy continuation rates in borderline-SCH subjects (P = 0.392). There was no difference in pregnancy outcomes based on TPOAb status and treatment for borderline-SCH subjects (P = 0.4214), or based on TPOAb status for euthyroid subjects (P = 0.2668).

CONCLUSIONS

Treatment of hypothyroidism in pregnancy should be initiated based on a TSH >4 mIU/l. Treatment initiation based on thyroid autoimmunity or a TSH >2.5 mIU/l may result in overtreatment.

Changes in subtypes of overt thyrotoxicosis and hypothyroidism following iodine fortification

OBJECTIVE

To investigate the impact of mandatory iodine fortification (IF) on the incidence of nosological subtypes of overt thyrotoxicosis and hypothyroidism.

DESIGN

We identified and scrutinized all possible new cases of overt thyrotoxicosis and hypothyroidism in an open cohort in Northern Jutland (n = 309 434; 1 January 1997) during the years 2014-2016. Individual medical history was evaluated to verify and detail the incidence of overt thyroid dysfunction and for classification into nosological subtypes. A number of cases were excluded during final verification due to spontaneous normalization of thyroid function, as they had no medical history suggesting a known condition, which could transiently affect thyroid function (subacute/silent thyroiditis, PPTD and iatrogenic thyroid dysfunction). An identical survey was conducted in 1997-2000 prior to mandatory IF of salt (13 µg/g) that was in effect from year 2001.

RESULTS

The standardized incidence rate (SIR) of verified overt thyrotoxicosis decreased markedly from 97.5/100 000/year in 1997-2000 to 48.8 in 2014-2016 (SIRR: 0.50 [95% CI: 0.45-0.56]). This was due to a distinct decrease in the SIR of multinodular toxic goitre (SIRR: 0.18 [0.15-0.23]), solitary toxic adenoma (SIRR: 0.26 [0.16-0.43]) and to a lesser degree Graves' disease (SIRR: 0.67 [0.56-0.79]). SIR for overt hypothyroidism was unaltered by 2014-2016 (SIRR: 1.03 [0.87-1.22]). However, age distribution shifted with more young and fewer elderly cases of verified overt hypothyroidism.

CONCLUSION

Mandatory IF caused a substantial reduction in SIR of verified overt thyrotoxicosis (especially of nodular origin) while avoiding an increase in SIR of verified overt hypothyroidism.

Levothyroxine Formulations: Pharmacological and Clinical Implications of Generic Substitution

Oral levothyroxine (LT4) is the standard therapy for patients with hypothyroidism. Oral LT4 is available in several formulations, including tablets, soft gel capsules and oral solution. Multiple brand-name and generic LT4 tablets are available. In the US, the Food and Drug Administration (FDA) has developed a protocol for establishing bioequivalence of LT4 formulations based on serum thyroxine (T4) levels after a single oral dose administered to healthy volunteers. This protocol has been criticized by professional endocrinology associations for using healthy individuals and ignoring serum thyroid-stimulating hormone (TSH) levels. In addition, the protocol did not initially correct for baseline T4 levels, although this was changed in a later version. There are concerns that the FDA's protocol could allow products with clinically significant differences in bioavailability to be declared therapeutically equivalent and interchangeable. Once a generic LT4 has been shown to be bioequivalent to a brand-name LT4, it may be substituted for that brand-name LT4 with no need for dose adjustment or follow-up therapeutic monitoring. Often, the substitution is made by the pharmacy without the physician's knowledge. Even small differences between LT4 formulations can cause significant changes in TSH levels. This may be a particular concern in vulnerable populations, including elderly, pregnant, and pediatric patients. Problems that can be encountered when switching between formulations or when original products are reformulated are discussed in this review. These problems include altered efficacy and adverse events, some of which can be caused by excipients. Patients should be maintained on the same LT4 preparation if possible. If the LT4 preparation is changed, TSH levels should be evaluated and, if necessary, the dose of LT4 adjusted.Funding: Merck.Plain Language Summary: Plain language summary available for this article.

Hypothyroidism in Context: Where We've Been and Where We're Going

Hypothyroidism affects up to 5% of the general population, with a further estimated 5% being undiagnosed. Over 99% of affected patients suffer from primary hypothyroidism. Worldwide, environmental iodine deficiency is the most common cause of all thyroid disorders, including hypothyroidism, but in areas of iodine sufficiency, Hashimoto’s disease (chronic autoimmune thyroiditis) is the most common cause of thyroid failure. Hypothyroidism is diagnosed biochemically, being overt primary hypothyroidism defined as serum thyroid-stimulating hormone (TSH) concentrations above and thyroxine concentrations below the normal reference range. Symptoms of hypothyroidism are non-specific and include mild to moderate weight gain, fatigue, poor concentration, depression, and menstrual irregularities, while the consequences of untreated or under-treated hypothyroidism include cardiovascular disease and increased mortality. Levothyroxine has long been the main tool for treating hypothyroidism and is one of the world’s most widely prescribed medicines. In adults with overt hypothyroidism, levothyroxine is usually prescribed at a starting dose of 1.6 µg/kg/day, which is then titrated to achieve optimal TSH levels (0.4–4.0 mIU/L), according to the therapeutic target. We here summarise the history of levothyroxine and discuss future issues regarding the optimal treatment of hypothyroidism. Because nearly one-third of patients with treated hypothyroidism still exhibit symptoms, it is important that levothyroxine is used more appropriately to achieve maximum benefit for patients. In order to ensure this, further research should include more accurate assessments of the true prevalence of hypothyroidism in the community, optimisation of the levothyroxine substitution dose, proper duration of treatment, and identification of patients who may benefit from combination therapy with levothyroxine plus levotriiodothyronine.

Funding: Merck.

Plain Language Summary: Plain language summary available for this article.

Hypothyroidism is one of the most common diseases worldwide, and levothyroxine is the usual medication prescribed to manage it. Hypothyroidism occurs when the thyroid gland, located in the neck, does not produce enough thyroid hormone for the body’s requirements. This can result in heart disease, infertility, and poor brain development in children. People with hypothyroidism may have changes in body weight, and feel tired, weak or unhappy, all of which can reduce their quality of life. In underdeveloped parts of the world, the main reason why people develop hypothyroidism is that they not getting enough iodine from food. Thus, many countries try to increase iodine intake by adding iodine to salt. In areas of the world where people ingest enough iodine, the most common cause of hypothyroidism is Hashimoto’s disease. This is an autoimmune disease in which the person’s immune system produces cells and antibodies that attack the thyroid gland. Most people with hypothyroidism will need to take levothyroxine for a long time, perhaps even for the rest of their lives. Levothyroxine replaces the person’s levels of thyroid hormone and makes them feel better, but the dose often needs to be adjusted for the best effect. In addition, many people with hypothyroidism do not know they have it. Research is ongoing to ensure that more people with hypothyroidism are diagnosed and are given effective treatment, and to work out the best way to use levothyroxine so that patients get the best results.

Previous Live Births and Induced Abortions May Precede Later Development of Graves' Hyperthyroidism

OBJECTIVE

To investigate the association between reproductive history and later development of various nosological subtypes of overt hyperthyroidism.

STUDY DESIGN

From the Danish population, we included incident hyperthyroid women, and for each case we recruited 4 euthyroid age-sex-region-matched controls from the same sub-population. Hyperthyroid cases/controls were: Graves' disease (GD, n = 232/928), multinodular toxic goitre (MNTG, n = 91/364), solitary toxic adenoma (STA, n = 21/84). Patients diagnosed with hyperthyroidism within 1 year after delivery including post-partum GD were excluded. In multivariate conditional regression models (reference: no reproductive events), we analysed the association between development of GD/MNTG/STA and reproductive factors such as age at menarche/menopause, reproductive span, number of pregnancies/childbirths/abortions, investigations for infertility, and years on oral contraceptives. We adjusted for possible confounders such as alcohol intake, smoking, co-morbidity, and education. Age was studied as a potential effect measure modifier.

RESULTS

GD patients diagnosed before the age of 40 years had given births more often than control subjects (OR [95% CI] for 1/2/3+ births [ref.: nulliparous] were 1.57 [0.80-3.11]/2.06 [1.001-4.22]/3.07 [1.50-6.26]), and they had induced abortions performed more often (OR for 1/2+ induced abortions [ref.: no: events] were 0.99 [0.54-1.84]/2.24 [1.12-4.45]). No associations were observed between any reproductive factor and the development of MNTG or STA.

CONCLUSIONS

Childbirths and induced abortions may be followed by development of Graves' hyperthyroidism after the post-partum period. This was not the case for the non-autoimmune subtypes of hyperthyroidism.

Age and Assay Related Changes of Laboratory Thyroid Function Tests in the Reference Female Population

Background

Laboratory thyroid function tests play a central role in the diagnosis of thyroid disorders. The aim of our cross-sectional study was to determine reference values for thyroid tests in a rigorously selected group of Montenegrin females, investigate the impact of possible age-related changes and the influence of the interassay bias between three frequently used immunoassays.

Methods

Female subjects were randomly selected, aged between 20 and 69 and 946 of them met the selection criteria. TSH, fT3, fT4, thyroid peroxidase and thyroglobulin antibodies were measured. Eighty samples were further analyzed on two other immunochemistry platforms.

Results

Median TSH progressively increased with age, there was no difference in fT3, while fT4 was significantly higher in the two oldest groups compared to the others. When using the age-related 97.5 percentile of TSH the percentage of reclassification was highest in the 20-29 years of age group (5.2%, p<0.05). In the oldest band, 7.7% had TSH values above cohort-specific and below the age-related upper reference limit. Bland-Altman bias plots revealed the highest interassay absolute mean difference between compared TSH assays of 24.5% and for fT4 assays of 13.8%.

Conclusions

The correlation coefficients between fT3 assays from different manufacturers were low. Serum TSH and fT4 concentrations increased with age and the implementation of age-specific TSH reference intervals would be of interest. The bias between the three commercial immunoassays indicated that the standardization of thyroid function tests is a task of great importance.

Clinical aspects of thyroid function during ageing

Globally, populations are ageing at a rapid rate. The increase in the number of older citizens is accompanied by an increased prevalence of thyroid dysfunction, one of the most common disorders in older people. However, the diagnosis of thyroid dysfunction in older people is hindered by several factors, including the scarcity of thyroid dysfunction symptoms in older people. We describe the physiological changes in thyroid function that occur with increasing age, focusing on literature regarding changes in thyroid function test results in older populations. We also discuss treatment considerations for clinical and subclinical thyroid dysfunction according to international guidelines for older people. Finally, we discuss the relationship between variations in thyroid function and common diseases of old age including cardiovascular disease, osteoporosis, cognitive impairment, and frailty and suggest directions for future research.

Thyrotoxicosis after iodine fortification. A 21-year Danish population-based study

OBJECTIVE

Monitoring the influence of cautious iodine fortification (IF) on the incidence rate of overt thyrotoxicosis in Denmark with formerly frequent multinodular toxic goitre.

DESIGN

A 21-year (1997-2017) prospective population-based study identified all new cases of overt biochemical thyrotoxicosis in two open cohorts: a Western cohort with moderate iodine deficiency (ID) and an Eastern cohort with mild ID (total n = 533 969 by 1 January 1997). A diagnostic algorithm was applied to all thyroid function tests performed within the study areas. Mandatory IF of salt was initiated in mid-2000 (13 ppm). This study is a part of DanThyr.

RESULTS

The standardized incidence rate (SIR) of thyrotoxicosis at baseline (1997-1998) was 128.5/100.000/year in the cohort with moderate ID and 80.1 in the cohort with mild ID. SIR increased markedly in both cohorts during the initial years of IF (moderate/mild ID: +39/+52% in 2000-2001/2004-2005) and subsequently decreased to baseline level (mild ID) or below (moderate ID) by 2008. The decline was due to a marked decrease in the incidence rate among elderly subjects and a moderate decrease among the middle aged. The follow-up period for the mildly iodine deficient cohort was restricted to 2008. A continuous decline in SIR was observed for the remainder of the study period in the area with moderate ID (33% below baseline in 2016-2017).

CONCLUSION

The rise in thyrotoxicosis incidence with cautious mandatory IF returned to baseline level after 7-8 years and levelled out at 33% below baseline in the population with previously moderate ID after 16-17 years.

Hyper- and hypothyroidism and gastrointestinal cancer risk: a Danish nationwide cohort study

OBJECTIVE

The association between thyroid dysfunction and gastrointestinal cancer is unclear.

DESIGN

We conducted a nationwide population-based cohort study to examine this potential association.

METHODS

We used Danish medical registries to assemble a nationwide population-based cohort of patients diagnosed with hyperthyroid or hypothyroid disease from 1978 through 2013. We computed standardized incidence ratios (SIRs) with corresponding 95% confidence intervals (CI) as measures of the relative risk of each cancer, comparing patients with thyroid dysfunction with that expected in the general population.

RESULTS

We included 163,972 patients, of which 92,783 had hyperthyroidism and 71,189 had hypothyroidism. In general, we found an increased risk of all gastrointestinal cancers within the first year after thyroid disease diagnosis. After more than five years of follow-up, patients with hyperthyroidism had a slightly increased risk of pancreatic and gallbladder and biliary tract cancer. Patients with hypothyroidism had a slightly increased risk of stomach, anal, liver, gallbladder and biliary tract, and pancreatic cancer after more than five years of follow-up, but the observed numbers of cancers were in general similar to the expected.

CONCLUSIONS

The increased risks of all gastrointestinal cancers in the first year following hyper- or hypothyroidism diagnosis are likely due to detection bias. After more than five years of follow-up, there does not seem to be a consistent causal association between thyroid disease and gastrointestinal cancer.

Reference intervals for thyrotropin in an area of Northern Italy: the Pordenone thyroid study (TRIPP)

PURPOSE

Thyrotropin (TSH) is the most accurate marker of thyroid dysfunction in the absence of pituitary or hypothalamic disease. Studies on TSH reference intervals (RIs) showed wide inter-individual variability and prompted an intense debate about the best estimation of TSH RIs.

DESIGN

We performed a population study on TSH RIs, using current data stored in the laboratory information system (LIS), at the Hospital Department of Laboratory Medicine, Pordenone (Italy), historically an area of mild-moderate iodine deficiency with a relatively high goiter prevalence.

METHODS

136,650 individuals constituted the final sample. A TSH immunoassay was performed on fasting serum samples with the Dimension Vista 1500 analyzer (Siemens Healthineers). We adopted the Kairisto's procedure to analyze TSH data downloaded by the LIS, applying the indirect strategy for deriving RIs.

RESULTS

TSH RIs of the entire population were 0.32-3.36 mIU/L with a distribution skewed towards higher values. RIs were 0.26-3.61 mIU/L for females, and 0.32-3.01 mIU/L for males. Unlike other studies, TSH median levels progressively decreased from 0-4 to 85-104 years in the overall population, both in male and in female subgroups, showing an inverse correlation between TSH and age in all groups.

CONCLUSIONS

This study is the first to analyze a high percentage (40%) of individuals from an ethnically homogenous Caucasian population. The results obtained emphasize the opportunity to define the TSH RIs according to age, gender and race, in addition to assay methods, and provide further insight about the possible role of iodine status.

Global epidemiology of hyperthyroidism and hypothyroidism

Thyroid hormones are essential for growth, neuronal development, reproduction and regulation of energy metabolism. Hypothyroidism and hyperthyroidism are common conditions with potentially devastating health consequences that affect all populations worldwide. Iodine nutrition is a key determinant of thyroid disease risk; however, other factors, such as ageing, smoking status, genetic susceptibility, ethnicity, endocrine disruptors and the advent of novel therapeutics, including immune checkpoint inhibitors, also influence thyroid disease epidemiology. In the developed world, the prevalence of undiagnosed thyroid disease is likely falling owing to widespread thyroid function testing and relatively low thresholds for treatment initiation. However, continued vigilance against iodine deficiency remains essential in developed countries, particularly in Europe. In this report, we review the global incidence and prevalence of hyperthyroidism and hypothyroidism, highlighting geographical differences and the effect of environmental factors, such as iodine supplementation, on these data. We also highlight the pressing need for detailed epidemiological surveys of thyroid dysfunction and iodine status in developing countries.

Temporal trends in thyroid-stimulating hormone (TSH) and thyroid peroxidase antibody (ATPO) testing across two phases of iodine fortification in Tasmania (1995-2013)

CONTEXT

Tasmania is an island state of the Australian Commonwealth with a well-documented history of mild iodine deficiency. Between 2001 and 2009, Tasmania experienced two incremental phases of iodine fortification.

OBJECTIVE

To examine trends in thyroid-stimulating hormone (TSH) and thyroid peroxidase antibody (ATPO) testing and their relationship to different phases of iodine nutrition in the Tasmanian population between 1995 and 2013.

DESIGN

Retrospective longitudinal study.

SETTING AND PARTICIPANTS

The major primary care and largest public hospital pathology providers in Tasmania submitted data for all TSH and ATPO tests performed between 1995 and 2013. Data linkage methodology was used to determine trends in TSH and ATPO testing.

RESULTS

A total of 1.66 million TSH assessments, involving 389,910 individual patients, were performed in Tasmania between 1995 and 2013. There was approximately a fourfold increase in the overall rate of TSH testing during this period with the rate of incident TSH assessment remaining relatively stable over the study period. The incidence of overt suppression and elevation of TSH (TSH≤0.1 mIU/L and ≥10 mIU/L) declined 62.3% and 59.7%, respectively, with a trend for increased incidence of borderline TSH elevation ≥4.0 mIU/L. The incidence of thyroid autoimmunity as determined by the proportion of abnormal ATPO results remained stable, with the absolute number of positive test results increasing during the study period.

CONCLUSION

Iodine supplementation of this mildly iodine-deficient population was not associated with an obvious increase in incidence of overt thyroid dysfunction or autoimmunity. Whilst the volume of TSH testing increased over the study period, the increase was driven by patients undergoing follow-up TSH assessments.

Latent Hypothyroidism in Adults

BACKGROUND

The prevalence of latent/subclinical hypothyroidism is between 3% and 10%, according to epidemiologic studies that have been carried out in the USA, the United Kingdom, and Denmark. As persons with latent hypo - thyroidism are often asymptomatic, the diagnosis is often made incidentally in routine laboratory testing.

METHODS

This review is based on a selective search in PubMed for publications on the diagnosis and treatment of latent hypothyroidism. All pertinent articles and guidelines published from 1 January 2000 to 31 July 2016 were included.

RESULTS

The diagnosis of latent hypothyroidism is generally assigned after repeated measurement of a TSH concentration above 4.0 mU/L in a person whose fT4 concentration is in the normal range. The most common cause is autoimmune thyroiditis, which can be detected by a test for autoantibodies. L-thyroxin supplementation is a controversial matter: its purpose is to prevent the development of overt hypothyroidism, but there is a danger of overtreatment, which increases the risk of fracture. To date, no benefit of L-thyroxin supplementation has been demonstrated with respect to morbidity and mortality, health-related quality of life, mental health, cognitive function, or reduction of overweight. There is, however, evidence of a beneficial effect on cardiac function in women, and on the vascular system. At present, treatment is generally considered indicated only if the TSH level exceeds 10.0 mU/L.

CONCLUSION

Limited data are available on the relevant clinical endpoints and undesired side effects of supplementation therapy. Physicians should advise patients about the indications for such treatment on an individual basis after due consideration of the risks and benefits.

MANAGEMENT OF ENDOCRINE DISEASE: Subclinical thyrotoxicosis: prevalence, causes and choice of therapy

Subclinical thyrotoxicosis is a condition affecting up to 10% of the population in some studies. We have reviewed literature and identified studies describing prevalences, causes and outcomes of this condition. Treatment should be considered in all subjects if this biochemical abnormality is persistent, especially in case of symptoms of thyrotoxicosis or in the presence of any complication. In particular, treatment should be offered in those subclinically thyrotoxic patients with a sustained serum TSH below 0.1 U/L. However it is important to recognise that there are no large controlled intervention studies in the field and thus there is no high quality evidence to guide treatment recommendations. In particular, there is no evidence for therapy and there is weak evidence of harm from thyrotoxicosis if serum TSH is in the 0.1-0.4 IU/L range. In this review, we describe the different causes of subclinical thyrotoxicosis, and how treatment should be tailored to the specific cause. We advocate radioactive iodine treatment to be the first-line treatment in majority of patients suffering from subclinical thyrotoxicosis due to multinodular toxic goitre and solitary toxic adenoma, but we do generally not recommend it as the first-line treatment in patients suffering from subclinical Graves' hyperthyroidism. Such patients may benefit mostly from antithyroid drug therapy. Subclinical thyrotoxicosis in early pregnancy should in general be observed, not treated. Moreover, we advocate a general restriction of therapy in cases where no specific cause for the presumed thyroid hyperactivity has been proven.

Direct Estimation of Reference Intervals for Thyroid Parameters in the Republic of Srpska

BACKGROUND

The aim of this study was to determine the reference values for thyrotropin (TSH), thyroid hormones (total and free thyroxine, T4 and fT4; total and free triiodothyronine, T3 and fT3), thyroglobulin (Tg) and thyroid antibodies (thyroid peroxidase, TPOAb and thyroglobulin antibody, TgAb) in the population of the Republic of Srpska.

METHODS

A total of 250 euthyroid subjects were enrolled in this study. A direct method for choosing reference subjects was used to establish reference intervals. The hormones and thyroid antibodies were measured by an electrochemiluminescence immunoassay method (ECLIA, Roche Diagnostics, Mannheim, Germany). We calculated the reference intervals by MedCalc, version 12.1.4.0 (MedCalc software, Belgium) as recommended by the IFCC (CLSI C28-A3).

RESULTS

Using guidelines recommended by the National Academy of Clinical Biochemistry (NACB) and based on standard statistical approaches, the reference intervals derived for TSH, fT4, T4, fT3, T3 were 0.75-5.32 mIU/L, 12.29-20.03 pmol/L, 73.49-126,30 nmol/L, 4.11-6.32 pmol/L, 1.15-2.32 nmol/L and for Tg, TPOAb, TgAb were 3.63-26.00 μg/L, <18.02 mIU/L, < 98.00 mIU/L, respectively. We found a significant difference (p<0.05) in TSH and fT3 values between different age groups as well as in T4, fT4 and fT3 values between ge nder groups.

CONCLUSIONS

The established reference values for the population of the Republic of Srpska were significantly different from the values recommended by the manufacturer of reagents (Roche Diagnostics). Our results showed that a laboratory needs to establish its own reference values in order to set up a proper diagnosis, as well as to treat patients successfully.

Thyroid Stimulating Hormone Reference Range and Prevalence of Thyroid Dysfunction in the Korean Population: Korea National Health and Nutrition Examination Survey 2013 to 2015

BACKGROUND

No nationwide epidemiological study evaluating the prevalence of subclinical and overt forms of hypothyroidism and hyperthyroidism has yet been conducted in Korea. This study aimed to evaluate the reference range of serum thyroid stimulating hormone (TSH) and the national prevalence of thyroid dysfunctions in Korea.

METHODS

Nation-wide cross-sectional data were analyzed from a representative sample of the civilian, non-institutionalized Korean population (n=6,564) who underwent blood testing for thyroid function and anti-thyroid peroxidase antibody (TPOAb) as part of the Korea National Health and Nutrition Examination Survey VI (2013 to 2015).

RESULTS

The reference interval of serum TSH in the Korean reference population was 0.62 to 6.68 mIU/L. Based on this reference interval, the prevalence of overt and subclinical hypothyroidism was 0.73% (males 0.40%, females 1.10%) and 3.10% (males 2.26%, females 4.04%), respectively. The prevalence of hypothyroidism increased with age until the age group between 50 to 59 years. Positive TPOAb were found in 7.30% of subjects (males 4.33%, females 10.62%). The prevalence of overt and subclinical hypothyroidism TPOAb-positive subjects was 5.16% and 10.88%, respectively. The prevalence of overt and subclinical hyperthyroidism was 0.54% (males 0.30%, females 0.81%) and 2.98% (males 2.43%, females, 3.59%), respectively.

CONCLUSION

The Serum TSH reference levels in the Korean population were higher than the corresponding levels in Western countries. Differences were found in the prevalence of hypothyroidism and hyperthyroidism according to age, sex, and TPOAb positivity. This study provides important baseline information for understanding patterns of thyroid dysfunction and diseases in Korea.

Association of iodized salt with goiter prevalence in Chinese populations: a continuity analysis over time

BACKGROUND

Iodine deficiency disorders (IDD) refer to diseases that are caused by insufficient iodine intake, and the best strategy to prevent IDD is the addition of iodine to dietary salt. Because iodine deficiency is a common cause of goiter, the prevalence as effectively controlled after the implementation of universal salt iodization (USI) in China. However, there is substantial controversy as to whether the incidence of thyroid disorders is related to iodized salt intake. Therefore, we aimed to clarify whether the risk of goiter can be promoted by USI.

METHODS

A longitudinal continuous study based on the national monitoring results of IDD in China was performed for 3 consecutive years. We recorded the following indicators of IDD from 31 provinces: goiter number, two degrees of goiter (the degree of goiter severity) and cretinism (three endemic diseases), iodized salt intake, median urinary iodine concentration (UIC), soil iodine content and coverage rates of iodized salt. One-way Analysis of Variance (ANOVA) and linear regression analyses examined the differences between the three groups and correlations, respectively. Data were collected from the Chinese national IDD surveillance data in 2011-2013, and the background values of Chinese soil elements were published in 1990.

RESULTS

A reference male's daily intake of maximum iodine was 378.9 μg, 379.2 μg and 366.9 μg in 2011, 2012, and 2013, respectively. No statistical association between daily iodized salt intake and the three endemic diseases was observed in 2011-2013 (P > 0.05). No association was observed between daily iodized salt intake and the UIC of children in 2011 (P > 0.05). Linear regression revealed no significant correlation between the soil iodine content and three endemic diseases. The present study indicated no difference in the daily iodized salt intake in each province during three years (F = 0.886, P = 0.647). The coverage rate of iodized salt remained above 98.7%, and goiter rates were stable in 2011-2013.

CONCLUSION

There was no significant association between iodized salt intake and the three endemic diseases, suggesting that the current nutrition level of iodized salt did not cause the high goiter prevalence.

Using Hashimoto thyroiditis as gold standard to determine the upper limit value of thyroid stimulating hormone in a Chinese cohort

BACKGROUND

Subclinical hypothyroidism, commonly caused by Hashimoto thyroiditis (HT), is a risk factor for cardiovascular diseases. This disorder is defined as merely having elevated serum thyroid stimulating hormone (TSH) levels. However, the upper limit of reference range for TSH is debated recently. This study was to determine the cutoff value for the upper normal limit of TSH in a cohort using the prevalence of Hashimoto thyroiditis as "gold" calibration standard.

METHODS

The research population was medical staff of 2856 individuals who took part in health examination annually. Serum free triiodothyronine (FT3), free thyroxine (FT4), TSH, thyroid peroxidase antibody (TPAb), thyroglobulin antibody (TGAb) and other biochemistry parameters were tested. Meanwhile, thyroid ultrasound examination was performed. The diagnosis of HT was based on presence of thyroid antibodies (TPAb and TGAb) and abnormalities of thyroid ultrasound examination. We used two different methods to estimate the cutoff point of TSH based on the prevalence of HT.

RESULTS

Joinpoint regression showed the prevalence of HT increased significantly at the ninth decile of TSH value corresponding to 2.9 mU/L. ROC curve showed a TSH cutoff value of 2.6 mU/L with the maximized sensitivity and specificity in identifying HT. Using the newly defined cutoff value of TSH can detect patients with hyperlipidemia more efficiently, which may indicate our approach to define the upper limit of TSH can make more sense from the clinical point of view.

CONCLUSIONS

A significant increase in the prevalence of HT occurred among individuals with a TSH of 2.6-2.9 mU/L made it possible to determine the cutoff value of normal upper limit of TSH.

Thyroid Function Characteristics and Determinants: The Rotterdam Study

BACKGROUND

Information on determinants and change of thyroid function over time is sparse and conflicting but crucial for clinical interpretation and research. Therefore, our aim was to systematically investigate determinants of thyroid-stimulating hormone (TSH), free thyroxine (FT4) (as markers of thyroid function), their mutual relation (as marker of thyroid function set point) and changes in thyroid function over time.

METHODS

We included 9402 participants from the Rotterdam Study not taking thyroid medication and with available thyroid function measurements. Repeated measurements (6.5-year interval) were available for 1225 participants. The association of selected determinants with TSH, FT4, and their mutual relation (reflecting thyroid function set point) was estimated using linear regression models using restricted cubic splines with three knots. The factors investigated were age, sex, body mass index (BMI), tobacco smoking, alcohol use, thyroperoxidase antibodies (TPOAb), and common genetic factors.

RESULTS

Most influential determinants of TSH were age, smoking, genetic determinants, and TPOAb levels (p < 0.001). For FT4, most influential determinants were age, BMI, sex, genetic determinants and TPOAb levels (p < 0.001). Older age, female sex, and increased TPOAb levels were associated with a stronger relation between TSH and FT4. TSH levels did not change over time, irrespective of age. FT4 levels increased over time, most prominently in those older than 65 years of age (mean increase of 4.5 pmol/L).

CONCLUSIONS

The main factors that influence the relationship between thyroid hormone and molar concentrations of TSH in our population-based cohort study are age, smoking, BMI, TPOAb levels, and common genetic variants. The set point that determines TSH secretion as it relates to negative thyroid hormone feedback is modified by age, sex and TPOAb positivity. FT4 levels increase over time, with a more pronounced increase in the elderly, while TSH values seem stable over time. Our results question the current notion of an increase of TSH with increasing age.

Urinary iodine, thyroid function, and thyroglobulin as biomarkers of iodine status

The accurate assessment of population iodine status is necessary to inform public health policies and clinical research on iodine nutrition, particularly the role of iodine adequacy in normal neurodevelopment. Urinary iodine concentration (UIC) directly reflects dietary iodine intake and is the most common indicator used worldwide to assess population iodine status. The CDC established the Ensuring the Quality of Iodine Procedures program in 2001 to provide laboratories that measure urinary iodine with an independent assessment of their analytic performance; this program fosters improvement in the assessment of UIC. Clinical laboratory tests of thyroid function (including serum concentrations of the pituitary hormone thyrotropin and the thyroid hormones thyroxine and triiodothyronine) are sometimes used as indicators of iodine status, although such use is often problematic. Even in severely iodine-deficient regions, there is a great deal of intraindividual variation in the ability of the thyroid to adapt. In most settings and in most population subgroups other than newborns, thyroid function tests are not considered sensitive indicators of population iodine status. However, the thyroid-derived protein thyroglobulin is increasingly being used for this purpose. Thyroglobulin can be measured in either serum or dried blood spot (DBS) samples. The use of DBS samples is advantageous in resource-poor regions. Improved methodologies for ascertaining maternal iodine status are needed to facilitate research on developmental correlates of iodine status. Thyroglobulin may prove to be a useful biomarker for both maternal and neonatal iodine status, but validated assay-specific reference ranges are needed for the determination of iodine sufficiency in both pregnant women and neonates, and trimester-specific ranges are possibly needed for pregnant women. UIC is currently a well-validated population biomarker, but individual biomarkers that could be used for research, patient care, and public health are lacking.

Serum thyroglobulin as a biomarker of iodine deficiency in adult populations

OBJECTIVE

To clarify which factors may influence the serum Tg level in an adult population and how this may affect Tg as a biomarker of iodine deficiency (ID).

DESIGN AND METHODS

Two identical cross-sectional studies were performed before (C1a: 1997-98, n = 4649) and after (C2: 2004-05, n = 3570) the Danish mandatory iodine fortification (IF) of salt (2000). Additionally, a follow-up study of C1a was performed after IF (C1b: 2008-10, n = 2465). The studies took place in two regions with mild (Copenhagen) and moderate (Aalborg) ID before IF. Serum Tg was measured by immunoradiometric method and investigated as outcome variable in multivariate models.

RESULTS

Multiple factors were associated with serum Tg. Some were directly related to iodine intake (cohort, urinary iodine concentration (UIC) level and region), and some were likely mediators of iodine intake effects on Tg (thyroid nodularity, thyroid size and autonomy with low TSH). Others were caused by Tg assay interference (Tg-Ab positivity), aggravation of ID (childbirths and smoking) or TSH stimulation of the thyroid. Estimated 24-h urinary iodine excretion was a more sensitive predictor of Tg than UIC. Iodine supplement users had low median Tg values compared with nonusers both before and after IF.

CONCLUSIONS

Multiple factors should be taken into consideration when evaluating Tg as a marker of ID in adult populations, and the Tg results may depend on the assay used. Still, Tg is a sensitive marker of ID. We suggest including a reference population with known sufficient iodine intake when Tg is used to evaluate ID.

Parity and 11-Year Serum Thyrotropin and Thyroid Autoantibody Change: A Longitudinal Population-Based Study

BACKGROUND

A role for female reproductive factors in the pathogenesis of thyroid autoimmunity has been suggested. This study investigated the prospective association between parity, abortion, use of oral contraceptive pill (OCP), and use of hormone replacement therapy (HRT), and 11-year change in serum thyrotropin (TSH), as well as change in thyroid peroxidase autoantibody (TPOAb) status.

METHODS

A random sample of 4649 people aged 18-65 years participated in a population-based study in the period 1997-1998. In the study presented here, 1749 non-pregnant women with no history of thyroid disease were included who participated in the 11-year follow-up examination in the period 2008-2010. Gynecological exposures were reported in a self-administered questionnaire at baseline and follow-up. TSH and TPOAb were measured at baseline and follow-up. Increased TPOAb status during follow-up was defined as a TPOAb below the assay cutoff (<30 kIU/L) at baseline and a TPOAb ≥30 kIU/L at follow-up. Multiple linear regression models were used, adjusted for age, smoking status, and urinary iodine excretion.

RESULTS

An inverse association was found between the number of years on HRT and the risk (odds ratio) of increased TPOAb status during follow-up (0.735 [confidence interval 0.558-0.968], p = 0.03). However, this association was not statistically significant when applying the Bonferroni adjusted significance level. The remaining reproductive factors showed no statistically significant association with risk of increased TPOAb during follow-up. Furthermore, parity, abortions, use of OCP, HRT use, age at menarche, and being pre- or postmenopausal were not significantly associated with 11-year TSH change.

CONCLUSIONS

No statistically significant association was found between the studied female reproductive measures and 11-year risk of TSH or TPO change. A possible protective role for HRT in the etiology of thyroid autoimmunity, however, deserves further research.

Thyroid function and autoimmunity in Danish pregnant women after an iodine fortification program and associations with obstetric outcomes

OBJECTIVE

Aberrations in maternal thyroid function and autoimmunity during pregnancy have been associated with negative obstetric outcome. In Denmark, a national iodine fortification program was implemented in the year 2000 with the aim to alleviate the mild-moderate iodine deficiency. Following the iodine implementation, there has been an increase in thyroid autoimmunity in the background population. This study investigates the thyroid status of pregnant Danish women following the iodine fortification program, and a possible association with preterm delivery.

DESIGN

Historical cohort study of 1278 randomly selected pregnant Danish women attending the national Down's syndrome screening program.

METHODS

The main outcome measures were thyroid status according to laboratory- and gestational-age-specific reference intervals, and association with risk of abnormal obstetric outcome. Antibody-positivity was defined as an antibody-level (thyroid peroxidase and/or thyroglobulin antibodies) above 60 U/ml.

RESULTS

Establishing laboratory-specific gestational-age-dependent reference intervals, we found a prevalence of maternal thyroid dysfunction of 10%-15.8% by use of the cut-off suggested by the American Thyroid Association. Thyroid dysfunction was significantly associated with antibody-positivity (P<0.05). No associations were found between preterm delivery and thyroid dysfunction (adjusted OR 0.6, 95% CI: 0.1-2.3) or autoimmunity (adjusted OR 1.1, 95% CI: 0.4-2.7).

CONCLUSIONS

After the implementation of the Danish iodine fortification program, the prevalence of thyroid dysfunction and autoimmunity in Danish pregnant women is high - even higher by use of pre-established reference intervals from international consensus guidelines. However, no associations were found with abnormal obstetric outcome. Large randomized controlled trials are needed to clarify the benefit of treating slight aberrations in pregnant women's thyroid function.

Gender differences in symptoms of hypothyroidism: a population-based DanThyr study

OBJECTIVES

We examined the gender-specific symptom prevalences in hypothyroidism and in healthy controls and explored the extent to which symptoms indicative of thyroid status may be different in women and men.

DESIGN AND METHODS

Patients newly diagnosed with overt autoimmune hypothyroidism (n = 140) and controls free of thyroid disease (n = 560) recruited from the same population participated in a population-based study of The Danish Investigation of Iodine Intake and Thyroid Diseases (DanThyr). Participants underwent a comprehensive programme including blood tests and completion of questionnaires. The gender-specific distribution of 13 hypothyroidism-associated symptoms and a simple combined score (0-13) was explored in conditional uni- and multivariate models taking into account a broad spectrum of possible confounders. Diagnostic odds ratios (DORs) were calculated as measures for the association between participant status (case vs control) and presence of symptoms (yes vs no).

RESULTS

In overt autoimmune hypothyroidism, 94·9% of women and 91·3% of men (P = 0·62) reported at least one of the hypothyroidism-associated symptoms, with tiredness as the most common symptom followed by dry skin and shortness of breath. In contrast, women free of thyroid disease self-reported at least one hypothyroidism-associated symptom considerably more often than men (73·7% vs 51·1%, P < 0·001). DORs (±SEM) for 0-1/2-3/4-13 symptoms were 0·07 (0·04-0·10)/2·15 (1·57-2·94)/7·99 (6·15-10·4) in men and 0·21 (0·16-0·28)/0·62 (0·58-0·66)/1·99 (1·90-2·09) in women.

CONCLUSION

The presence of symptoms is more indicative for overt autoimmune hypothyroidism in men than in women, and presumably persistent symptoms after therapy of hypothyroidism will be more common in women.

Impaired Fertility Associated with Subclinical Hypothyroidism and Thyroid Autoimmunity: The Danish General Suburban Population Study

INTRODUCTION

The aim of this study was to estimate the significance of TSH, thyroid peroxidase antibody (TPOAb), and mild (subclinical) hypothyroidism in women from The Danish General Suburban Population Study (GESUS) on the number of children born, the number of pregnancies, and the number of spontaneous abortions.

METHODS

Retrospective cross sectional study of 11254 women participating in GESUS. Data included biochemical measurements and a self-administrated questionnaire.

RESULTS

6.7% had mild (subclinical) hypothyroidism and 9.4% prevalent hypothyroidism. In women with mild hypothyroidism TPOAb was significantly elevated and age at first child was older compared to controls. TSH and TPOAb were negatively linearly associated with the number of children born and the number of pregnancies in the full cohort in age-adjusted and multiadjusted models. TSH or TPOAb was not associated with spontaneous abortions. Mild (subclinical) hypothyroidism was associated with a risk of not having children and a risk of not getting pregnant in age-adjusted and multiadjusted models. Prevalent hypothyroidism was not associated with the number of children born, the number of pregnancies, or spontaneous abortions.

CONCLUSION

Impaired fertility is associated with TSH, TPOAb, and mild (subclinical) hypothyroidism in a Danish population of women.

External validation of a normal tissue complication probability model for radiation-induced hypothyroidism in an independent cohort

BACKGROUND

A normal tissue complication probability (NTCP) model for radiation-induced hypothyroidism (RIHT) was previously derived in patients with squamous cell carcinoma of the head and neck (HNSCC) discerning thyroid volume (Vthyroid), mean thyroid dose (Dmean), and latency as predictive factors. The purpose of this study was to test the performance of this model in an independent cohort of patients receiving primary radiotherapy (RT) for HNSCC.

MATERIAL AND METHODS

A validation cohort of 198 patients with HNSCC was included after plasma thyrotropin (TSH) assessment. RIHT was defined as TSH > 4.0 mU/l from blood samples obtained during follow-up. A new mixture NTCP model was developed from the validation cohort after multivariable analysis. Due to only one follow-up TSH assessment in the validation cohort, the time factor derived from the original cohort was fixed in a mixture model and applied for the NTCP validation. Association between model predictions of the initial model and observed clinical outcome in the validation cohort was investigated by applying the previous model (Vthyroid, Dmean and time) on the new cohort and comparing it to the clinical outcome.

RESULTS

Both Dmean and Vthyroid were confirmed as significant risk factors for RIHT in the validation cohort, odds ratio (OR) 1.19 (1.1-1.37) and OR 0.75 (0.57-0.9), respectively. A small difference in overall probability of RIHT was observed between the cohorts, further analysis indicated this to be related to less frequent blood tests in the validation cohort relative to the original cohort. However, Pearson's correlation coefficients between model and clinical outcome were high: r = 0.97 estimated by the original model versus the original cohort, and r = 0.97 estimated by the original model versus the new cohort.

CONCLUSION

Dmean and Vthyroid were significant predictors of RIHT in both cohorts. The original NTCP model demonstrated external validity owing to high Pearson's correlation coefficients between estimated and observed incidence rates of RIHT in the original as well as in the validation cohort. This model may facilitate clinically relevant estimations of RIHT after RT to the neck.

Thyrotropin versus age relation as an indicator of historical iodine intake

BACKGROUND

In populations with mild iodine deficiency, the serum level of thyrotropin (TSH) is negatively and the serum free thyroxine (FT4) is positively associated with age. An ongoing decrease of TSH and increase of FT4 can be found after iodine supplementation. The aim of this study was to investigate whether there are current differences in the relation between thyroid function and age in relation to differences in iodine intake in the past.

METHODS

Eight medical laboratories in several regions of The Netherlands, which are all iodine sufficient at present but with a difference in iodine status in the past, provided the results of all TSH and FT4 measurements performed from 2006 until 2011, resulting in 330,802 TSH and 103,940 FT4 measurements.

RESULTS

The negative association between TSH and age in the elderly is only present in areas with a historical iodine deficiency (regression coefficients [RC] -0.008, 95% confidence interval [CI] -0.009; -0.007). In the historically iodine-sufficient population, TSH shows no obvious increase or decrease with age. In both the historically iodine-sufficient and iodine-deficient populations, FT4 levels were positively associated with age in the elderly (RC 0.009, 95% CI 0.008; 0.010 and RC 0.008, 95% CI 0.007; 0.010, respectively).

CONCLUSIONS

There are differences in relation between thyroid function and age between populations with differences in iodine intake in the past, despite an adequate iodine status at present. This raises the question whether the present but also historical iodine status of a population should be taken into account when establishing the reference limits of TSH and FT4.

Clinical manifestations in ten patients with asymptomatic metal-on-metal hip arthroplasty with very high cobalt levels

Reports of adverse reactions to metal particle debris with metal-on-metal (MoM) hip arthroplasty have increased recently. Apart from the formation of pseudotumours and higher revision rates, another major cause for concern are the systemic effects of metal ions. Several effects of elevated systemic cobalt ions have been reported (e.g., myocardial and neurological effects, hypothyroidism). All 643 patients who underwent a stemmed large head MoM total hip replacement in our clinic were screened with repeated whole blood samples of metal ions (cobalt, chromium). We included ten asymptomatic unrevised patients with the highest cobalt concentrations, determined at a minimum of three years after implantation. These patients were subjected to an extensive neurological and cardiological screening protocol. In addition, blood samples were taken to assess renal and thyroid function. Ten patients with a cobalt level of 18-153 µg/L (mean 46.8 µg/L) were included. Nine patients were female, mean age was 65 years (range 56-75). The mean follow-up period was 4.2 years (range 3.0-6.1). Seven patients had bilateral stemmed MoM hip arthroplasty. No signs or symptoms of neurological dysfunction, cardiomyopathy, or renal or thyroid dysfunction could be identified or attributed to elevated cobalt levels. The clinical relevance of this study is that after short-term follow-up highly elevated blood cobalt levels do not cause systemic effects in our population. Hence in asymptomatic patients metal ions appear not to be a significant factor in the decision of when to revise a MoM large head total hip replacement.

Iodine deficiency and thyroid disorders

Iodine deficiency early in life impairs cognition and growth, but iodine status is also a key determinant of thyroid disorders in adults. Severe iodine deficiency causes goitre and hypothyroidism because, despite an increase in thyroid activity to maximise iodine uptake and recycling in this setting, iodine concentrations are still too low to enable production of thyroid hormone. In mild-to-moderate iodine deficiency, increased thyroid activity can compensate for low iodine intake and maintain euthyroidism in most individuals, but at a price: chronic thyroid stimulation results in an increase in the prevalence of toxic nodular goitre and hyperthyroidism in populations. This high prevalence of nodular autonomy usually results in a further increase in the prevalence of hyperthyroidism if iodine intake is subsequently increased by salt iodisation. However, this increase is transient because iodine sufficiency normalises thyroid activity which, in the long term, reduces nodular autonomy. Increased iodine intake in an iodine-deficient population is associated with a small increase in the prevalence of subclinical hypothyroidism and thyroid autoimmunity; whether these increases are also transient is unclear. Variations in population iodine intake do not affect risk for Graves' disease or thyroid cancer, but correction of iodine deficiency might shift thyroid cancer subtypes toward less malignant forms. Thus, optimisation of population iodine intake is an important component of preventive health care to reduce the prevalence of thyroid disorders.

The management of thyroid nodules: a retrospective analysis of health insurance data

BACKGROUND

In Germany, about 59 000 thyroid operations are performed each year for uni- or multinodular goiter, most of them for diagnostic purposes. The rate of detection of thyroid cancer in such operations is relatively low, at 1:15. Evidence suggests that the preoperative tests recommended in guidelines for estimating the risk of cancer are not being performed as often as they should. In the present study, we determined the measures that were actually taken to diagnose and treat thyroid nodules and compared the findings with the guideline recommendations.

METHOD

We retrospectively analyzed data from a single, large statutory healthinsurance carrier in Germany (AOK), determining the diagnostic and therapeutic measures that were reimbursed for 25 600 patients in whom a uni- or multinodular goiter was newly diagnosed in the second quarter of 2006 (none of these patients had carried such a diagnosis 1 year previously). We recorded the diagnostic measures performed in the preceding 9 months and all other tests and treatments, including surgery and radioactive iodine treatment, in the 2 years thereafter.

RESULTS

Among patients who underwent surgery for uninodular goiter, the preoperative diagnostic studies included ultrasonography (in 100% of patients), scintigraphy (94%), measurement of thyroid-stimulating hormone (95%), measurement of calcitonin (9%), and fine-needle aspiration cytology (FNAC)(21%). An ultrasonographic examination was billed for only 28% of patients with uninodular goiter in the two years after the diagnosis was made. 13% of patients with uninodular goiter who were not operated on were given L-thyroxine, even though this is against guideline recommendations.

CONCLUSION

Inadequate preoperative risk stratification of thyroid nodules may explain the large number of thyroid operations that are performed for diagnostic purposes, resulting in a low percentage of malignancies detected. Preoperative FNAC and calcitonin measurement should be used in the diagnostic evaluation of thyroid nodules far more often than this is now done. As a rule, follow-up ultrasonography should be performed for all thyroid nodules that are not operated on. Patients with non-operated thyroid nodules should not be given thyroxine. A limitation of this study is that diagnostic measures were only recorded if they were performed in the 9 months before surgery, with earlier diagnostic measures (if any) being missed.

Thyroid nodules in an 11-year DanThyr follow-up study

CONTEXT

Limited longitudinal data are available on changes in the thyroid gland structure in a population and how this is influenced by iodine fortification (IF).

OBJECTIVE

Our objective was to clarify how IF influenced thyroid gland structure in 2 regions with different iodine intake at baseline (Copenhagen, mild iodine deficiency [ID]; Aalborg, moderate ID).

DESIGN AND SETTING

We conducted a longitudinal population-based study (DanThyr) where participants were examined before (1997) and after (2008) the Danish mandatory IF of salt (2000).

PARTICIPANTS

We examined 2465 adults, and ultrasonography was performed by the same sonographers using the same equipment, after controlling performances.

MAIN OUTCOME MEASURE

Change in thyroid gland structure was evaluated.

RESULTS

The follow-up period saw an increased prevalence of multinodularity (9.8%-13.8 %, P < .001), especially in the previously moderate ID region of Aalborg (9.1%-15.4%, P < .001), whereas no change in prevalence was seen for solitary nodules (5.6%-5.1%, P = .34). In individual participants, changes in thyroid structure and disappearance of thyroid nodules during the 11 years was common with an overall normalization rate of 21.2 (95% confidence interval [CI] = 17.9-24.9) per 1000 person-years. Solitary nodules had a significantly higher normalization rate than multiple nodules (normalization rate ratio 0.47 [95% CI = 0.32-0.67]). A regional difference (Aalborg vs Copenhagen) was seen between normalization rates of multiple nodules (normalization rate ratio 0.29 [95% CI = 0.12-0.64]), but not for solitary nodules (normalization rate ratio 0.81 [95% CI = 0.53-1.21]).

CONCLUSIONS

Changes in the thyroid gland structure with both appearance and disappearance of thyroid nodules are common after an iodization program.

Hypothyroid symptoms and the likelihood of overt thyroid failure: a population-based case-control study

BACKGROUND

It is generally accepted that patients suffering from hypothyroidism may express few symptoms, but this has not been studied in a population-based study design.

OBJECTIVES

To study the array of symptoms as they are reported in newly diagnosed overt autoimmune hypothyroidism using a population-based case-control design.

METHODS

Patients with new overt autoimmune hypothyroidism (n=140) and their individually matched thyroid disease-free controls (n=560) recruited from the same population underwent a comprehensive program and self-reported a number of symptoms. We identified the symptoms associated with overt hypothyroidism and calculated positive (LR+) and negative (LR-) likelihood ratios as well as diagnostic odds ratios (DORs) as measures for the association between disease state and symptoms.

RESULTS

Among 34 symptoms investigated, 13 symptoms were statistically overrepresented in hypothyroidism. Hypothyroid patients suffered mostly from tiredness (81%), dry skin (63%), and shortness of breath (51%). Highest DORs (95% CI) were reported for tiredness (5.94 (3.70-9.60)), hair loss (4.58 (2.80-7.51)), and dry skin (4.09 (2.73-6.16)). A hypothyroidism-component-score was defined as the number of hypothyroidism-associated symptoms (range: 0-13). LR+ for participants with a hypothyroidism-component-score of 0 was 0.21 (0.09-0.39), meaning that the post-test probability was lowered to 21% of what it was before asking for symptoms. LR+ for scores of 1-2/3/4-6/7-9/10-13 were: 0.47 (0.30-0.72)/1.16 (0.70-1.87)/1.90 (1.29-2.45)/3.52 (2.30-5.36)/6.29 (2.30-17.7).

CONCLUSIONS

None of the individual symptoms of hypothyroidism had high LRs or DORs. Thus, neither the presence nor absence of any individual hypothyroidism symptom was reliable in the decision making of who should have their thyroid function tested. Therefore, even minor suspicion should lead to a blood test.

Influence of iodization programmes on the epidemiology of nodular goitre

Iodine is essential for the synthesis of thyroid hormones. Iodine deficiency can affect human health in different ways, and is commonly referred to as iodine deficiency disorders (IDD). These range from defective development of the central nervous system during the fetal-neonatal life, to goitre in the adult. Only a few countries were completely iodine sufficient before 1990. Since then, a major effort has been made to introduce salt iodization to ensure sufficient intake of iodine in deficient areas. Iodine prophylaxis has been shown to exert a pivotal role in abating goitre and other iodine-deficiency disorders, and has also been shown to modulate the pattern of thyroid diseases. An increased frequency of thyroid autoimmunity and of hypothyroidism has been observed after introducing iodization programmes. Nevertheless, available evidence clearly confirms that the benefits of correcting iodine deficiency, consisting mainly of reducing nodular goitre and non-autoimmune hyperthyroidism, far outweigh the risks of iodine supplementation.

The association of thyroid nodule with non-iodized salt among Chinese children

Objective

The controversy that iodized salt may increase the risk of thyroid disorders has been aroused in China during the past decade. Most of studies focused on adult rather than children. We aimed to explore whether iodized salt was associated with an increased risk of thyroid nodule in Chinese children.

Methods

The cross-sectional study was conducted in Hangzhou, China, in 2010. Iodized salt intake, urine iodine concentration (UIC) and thyroid nodule (by ultrasonography) were measured in 3026 children. The associations of iodized salt with thyroid nodule were evaluated using multiple logistic regression models.

Results

The prevalence of thyroid nodule was 10.59% among Chinese children. Girls (11.89%) had higher prevalence of thyroid nodule than boys (9.26%). No significant association was observed between type of salt and thyroid nodule in pooled samples, boys and girls, respectively. Similar associations were observed between UIC and thyroid nodule. There was no significant association between milk consumption and thyroid nodule as well.

Conclusion

The present study indicated that non-iodized salt may not increase the risk of thyroid nodules among Chinese children. Similar associations were observed between milk consumption, UIC and thyroid nodules.

Development of autoimmune overt hypothyroidism is highly associated with live births and induced abortions but only in premenopausal women

CONTEXT

The 1-year postpartum period is often accompanied by increased risk for thyroid disease.

OBJECTIVE

The objective of the study was to investigate the role of reproductive risk factors in the development of autoimmune overt hypothyroidism in the years after the 1-year postpartum period.

DESIGN, SETTING, AND SUBJECTS

In a population study, we included Danish women with new autoimmune overt hypothyroidism not diagnosed within the first year after a pregnancy (n = 117; median age 53.0 y) and age- and region-matched euthyroid controls from the same population (n = 468).

MAIN OUTCOME MEASURES

In conditional multivariate logistic regression models, we analyzed the associations between the development of autoimmune hypothyroidism and age at menarche/menopause, years of menstruations, pregnancies, spontaneous and induced abortions, live births, and years on oral contraceptives and postmenopausal hormone replacement therapy, also taking various possible confounders into account.

RESULTS

In multivariate regression models with no event as reference, the odds ratios (ORs) for hypothyroidism [95% confidence interval (CI)] after one/two/three or more live births were 1.72 (0.56-5.32)/3.12 (1.14-8.48)/4.51 (1.65-12.3) and 1.02 (0.57-1.81)/2.70 (1.27-5.75) after one/two or more induced abortions. Findings were valid only for women having hypothyroidism diagnosed before the age of 55 years. We found no association between disease development and other reproductive risk factors investigated.

CONCLUSIONS

Previous live births and induced abortions were major risk factors for the development of autoimmune overt hypothyroidism in women aged up to 55 years. The increased risk for hypothyroidism after giving birth extends longer than just to the 1-year postpartum period, and numbers of previous pregnancies should be taken into account when evaluating the risk of hypothyroidism in a young women.