The Danish investigation on iodine intake and thyroid disease (DanThyr): history and implications

Due to mild-to-moderate iodine deficiency in Denmark, health authorities initiated a voluntary iodine fortification (IF) program in 1998, which became mandatory in 2000. In line with recommendations from the World Health Organization, the Danish investigation on iodine intake and thyroid disease (DanThyr) was established to monitor the effect on thyroid health and disease. The program involved different study designs and followed two Danish sub-populations in the years before IF and up till 20 years after. Results showed that the IF was successfully implemented and increased the level of iodine intake from mild-moderate iodine deficiency to low adequacy. The level of thyroglobulin and thyroid volume decreased following IF, and there was an indication of fewer thyroid nodules. The incidence of hyperthyroidism increased transiently following IF but subsequently decreased below the pre-fortification level. Conversely, thyroid-stimulating hormone levels and the prevalence of thyroid autoimmunity increased along with an increase in the incidence of hypothyroidism. These trends were mirrored in the trends in treatments for thyroid disease. Most differences in thyroid health and disease between regions with different iodine intake levels before IF attenuated. This review illustrates the importance of a monitoring program to detect both beneficial and adverse effects and exemplifies how a monitoring program can be conducted when a nationwide health promotion program - as IF - is initiated.

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.

Improving empowerment, motivation, and medical adherence in patients with poorly controlled type 2 diabetes: A randomized controlled trial of a patient-centered intervention

OBJECTIVE

To test whether an intervention consisting of four patient-centered consultations improves glycemic control and self-management skills in patients with poorly regulated type 2 diabetes (T2DM), compared to a control group receiving usual care.

METHODS

Unblinded parallel randomized controlled trial including 97 adults diagnosed with T2DM ≥ 1 year and hemoglobin A1c (HbA1c) levels ≥ 8.0% (64 mmol/mol). Consultations incorporated tools supporting self-reflection, learning processes, and goal setting. Primary outcome was HbA1c. Secondary outcomes were autonomy support, motivation, self-management skills, and well-being.

RESULTS

Average HbA1c decreased slightly in both groups. Autonomy support and frequency of healthy eating were significantly higher in the intervention group. Most participants in the intervention group chose to set goals related to diet and physical exercise. Implementation of the intervention was inconsistent.

CONCLUSION

Despite increased autonomy support and individual goal-setting, the intervention was not superior to usual care in terms of glycemic control. More research is needed on how individual preferences and goals can be supported in practice to achieve sustainable behavior changes.

PRACTICE IMPLICATIONS

The intervention promoted participant engagement and supported exploration of participants' challenges and preferences. Further exploration of more flexible use of tools adapted to individual contexts is recommended.

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.

Increased Incidence Rate of Hypothyroidism After Iodine Fortification in Denmark: A 20-Year Prospective Population-Based Study

OBJECTIVE

To monitor the impact of a cautious iodine fortification (IF) on the incidence of overt hypothyroidism in two subpopulations with different levels of preexisting iodine deficiency (ID).

DESIGN

A 20-year (1997 to 2016) prospective population-based study identified all new cases of diagnosed overt biochemical hypothyroidism in two open cohorts: a western cohort with moderate ID (n = 309,434; 1 January 1997) and an eastern cohort with mild ID (n = 224,535; 1 January 1997). A diagnostic algorithm was applied to all thyroid function tests performed within the study areas, and possible new cases were verified individually. Mandatory IF of salt was initiated in mid-2000 (13 ppm). The current study is a part of the DanThyr study.

RESULTS

At baseline, standardized incidence rates (SIRs) of hypothyroidism were 32.9 and 47.3/100.000/y in the cohorts with moderate and mild ID, respectively. The SIR of hypothyroidism increased significantly in both cohorts after implementing mandatory IF, with peak values of 150% in 2014 to 2016 for the moderate ID cohort and 130% in 2004 to 2005 for the mild ID cohort. Significant increases in SIR were seen among the young and middle-aged participants of both cohorts, whereas no changes were seen among the elderly participants (≥60 years). The follow-up period for the mildly iodine-deficient cohort was restricted up to and including 2008.

CONCLUSION

The cautious initiation of the IF program in Denmark caused a sustained increase in hypothyroidism incidence among subjects residing in areas of moderate and mild ID but only among the young and middle-aged participants.

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.

Iodine deficiency in pregnancy is prevalent in vulnerable groups in Denmark

INTRODUCTION

Iodine is essential for the production of thyroid hormones. In pregnancy, physiological changes occur that can lead to iodine deficiency and impairment of fetal neurological development. We aimed to assess the iodine intake in pregnant women in Eastern Denmark, compare iodine levels in Eastern and Western Denmark and to identify potentially vulnerable groups.

METHODS

This was a cross-sectional cohort study of pregnant Danish women (n = 240). Questionnaires and urine samples were collected at the Ultrasound Clinic, Hvidovre Hospital, Denmark, and urinary iodine concentrations (UIC) (µg/l) were measured. Predictors of iodine supplement use were examined by multivariate logistic regression models.

RESULTS

The pregnant women from Eastern Denmark had a median age of 30 years and the median gestational week at which they were included in the study was week 19. The majority took iodine-containing supplements (86%). The median UIC was 118 (interquartile range (IQR): 79-196) µg/l in iodine supplement users and 82 (IQR: 41-122) µg/l in non-users (p < 0.001). Predictors of not using iodine supplement in Eastern and Western Denmark were short maternal education, non-Danish origin and pre-pregnancy obesity.

CONCLUSIONS

The iodine status in Danish pregnant women was below WHO recommendations. Iodine supplement non-users are at a particular risk of iodine deficiency. Low maternal education, non-Danish origin and pre-pregnancy obesity are predictors of non-iodine supplement use. An increase in iodine fortification may be recommended to improve the iodine status in pregnant Danish women.

FUNDING

none.

TRIAL REGISTRATION

not relevant.

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.

Iodine status in the Nordic countries - past and present

Background

Adequate iodine nutrition is dependent on ground water content, seafood, and, as many countries use iodized cow fodder, dairy products. In most countries, salt fortification programs are needed to assure adequate iodine intake.

Objectives

The objectives are threefold: 1) to describe the past and present iodine situation in the Nordic countries, 2) to identify important gaps of knowledge, and 3) to highlight differences among the Nordic countries’ iodine biomonitoring and fortification policies.

Design

Historical data are compared with the current situation. The Nordic countries’ strategies to achieve recommended intake and urine iodine levels and their respective success rates are evaluated.

Results

In the past, the iodine situation ranged from excellent in Iceland to widespread goiter and cretinism in large areas of Sweden. The situation was less severe in Norway and Finland. According to a 1960 World Health Organization (WHO) report, there were then no observations of iodine deficiency in Denmark. In Sweden and Finland, the fortification of table salt was introduced 50–75 years ago, and in Norway and Finland, the fortification of cow fodder starting in the 1950s helped improve the population's iodine status due to the high intake of milk. In Denmark, iodine has been added to household salt and salt in bread for the past 15 years. The Nordic countries differ with regard to regulations and degree of governmental involvement. There are indications that pregnant and lactating women, the two most vulnerable groups, are mildly deficient in iodine in several of the Nordic countries.

Conclusion

The Nordic countries employ different strategies to attain adequate iodine nutrition. The situation is not optimal and is in need of re-evaluation. Iodine researchers, Nordic national food administrations, and Nordic governmental institutions would benefit from collaboration to attain a broader approach and guarantee good iodine health for all.

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.

Serum thyroglobulin before and after iodization of salt: an 11-year DanThyr follow-up study

OBJECTIVE

Our objective was to investigate individual serum thyroglobulin (Tg) changes in relation to iodine fortification (IF) and to clarify possible predictors of these changes.

DESIGN

We performed a longitudinal population-based study (DanThyr) in two regions with different iodine intake at baseline: Aalborg (moderate iodine deficiency (ID)) and Copenhagen (mild ID). Participants were examined at baseline (1997) before the mandatory IF of salt (2000) and again at follow-up (2008) after IF.

METHODS

We examined 2465 adults and a total of 1417 participants with no previous thyroid disease and without Tg-autoantibodies were included in the analyses. Serum Tg was measured by immunoradiometric method. We registered participants with a daily intake of iodine from supplements in addition to IF.

RESULTS

Overall, the follow-up period saw no change in median Tg in Copenhagen (9.1/9.1 μg/l, P=0.67) while Tg decreased significantly in Aalborg (11.4/9.0 μg/l, P<0.001). Regional differences were evident before IF (Copenhagen/Aalborg, 9.1/11.4 μg/l, P<0.001), whereas no differences existed after IF (9.1/9.0 μg/l, P=1.00). Living in Aalborg (P<0.001) and not using iodine supplements at baseline (P=0.001) predicted a decrease in Tg whereas baseline thyroid enlargement (P=0.02) and multinodularity (P=0.01) were associated with an individual increase in Tg during follow-up.

CONCLUSIONS

After IF we observed a decrease in median Tg in Aalborg and the previously observed regional differences between Aalborg and Copenhagen had levelled out. Likewise, living in Aalborg was a strong predictor of an individual decrease in serum Tg. Thus, even small differences in iodine intake at baseline were very important for the individual response to IF.

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.

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.

Thyroid function and body weight: a community-based longitudinal study

Objective

Body weight and overt thyroid dysfunction are associated. Cross-sectional population-based studies have repeatedly found that thyroid hormone levels, even within the normal reference range, might be associated with body weight. However, for longitudinal data, the association is less clear. Thus, we tested the association between serum thyrotropin (TSH) and body weight in a community-based sample of adult persons followed for 11 years.

Methods

A random sample of 4,649 persons aged 18–65 years from a general population participated in the DanThyr study in 1997–8. We included 2,102 individuals who participated at 11-year follow-up, without current or former treatment for thyroid disease and with measurements of TSH and weight at both examinations. Multiple linear regression models were used, stratified by sex and adjusted for age, smoking status, and leisure time physical activity.

Results

Baseline TSH concentration was not associated with change in weight (women, P = 0.17; men, P = 0.72), and baseline body mass index (BMI) was not associated with change in TSH (women, P = 0.21; men, P = 0.85). Change in serum TSH and change in weight were significantly associated in both sexes. Weight increased by 0.3 kg (95% confidence interval [CI] 0.1, 0.4, P = 0.005) in women and 0.8 kg (95% CI 0.1, 1.4, P = 0.02) in men for every one unit TSH (mU/L) increase.

Conclusions

TSH levels were not a determinant of future weight changes, and BMI was not a determinant for TSH changes, but an association between weight change and TSH change was present.

Iodine fortification may influence the age-related change in thyroid volume: a longitudinal population-based study (DanThyr)

OBJECTIVE

To assess the individuals' thyroid volume changes after the mandatory nationwide iodine fortification (IF) program in two Danish areas with different iodine intake at baseline (Copenhagen, mild iodine deficiency (ID) and Aalborg, moderate ID).

DESIGN

A longitudinal population-based study (DanThyr).

METHODS

We examined 2465 adults before (1997) and after (2008) the Danish IF of salt (2000). Ultrasonography was carried out by the same sonographers using the same equipment, after controlling performances. Participants treated for thyroid disease were excluded from analyses.

RESULTS

Overall, median thyroid volume had increased in Copenhagen (11.8-12.2 ml, P=0.001) and decreased in Aalborg, although not significantly (13.3-13.1 ml, P=0.07) during the 11 years of follow-up. In both regions, there was an age-related trend in individual changes in thyroid volume from baseline to follow-up; thyroid volume increased in women <40 years of age and decreased in women >40 years of age. IN A MULTIVARIATE REGRESSION MODEL, HIGHER AGE AT ENTRY WAS A PREDICTOR (P0.05) FOR THYROID VOLUME DECREASE 20% DURING THE FOLLOW-UP PERIOD (WOMEN AGED 4045 YEARS: odds ratio (OR) 4.3 (95% CI, 2.2-8.2); women aged 60-65 years: 5.8 (2.9-11.6)) and individuals of higher age were also less likely to have an increase in thyroid volume (women aged 40-45 years: OR 0.2 (0.1-0.3); women aged 60-65: OR 0.3 (0.2-0.4)).

CONCLUSIONS

Age-dependent differences in thyroid volume and enlargement had leveled out after the Danish iodization program. Thus, the previously observed increase in thyroid volume with age may have been caused by ID.

Common variants in CYP2R1 and GC genes predict vitamin D concentrations in healthy Danish children and adults

Environmental factors such as diet, intake of vitamin D supplements and exposure to sunlight are known to influence serum vitamin D concentrations. Genetic epidemiology of vitamin D is in its infancy and a better understanding on how genetic variation influences vitamin D concentration is needed. We aimed to analyse previously reported vitamin D-related polymorphisms in relation to serum 25(OH)D concentrations in 201 healthy Danish families with dependent children in late summer in Denmark. Serum 25(OH)D concentrations and a total of 25 SNPs in GC, VDR, CYP2R1, CYP24A1, CYP27B1, C10or88 and DHCR7/NADSYN1 genes were analysed in 758 participants. Genotype distributions were in Hardy-Weinberg equilibrium for the adult population for all the studied polymorphisms. Four SNPs in CYP2R1 (rs1562902, rs7116978, rs10741657 and rs10766197) and six SNPs in GC (rs4588, rs842999, rs2282679, rs12512631, rs16846876 and rs17467825) were statistically significantly associated with serum 25(OH)D concentrations in children, adults and all combined. Several of the SNPs were in strong linkage disequilibrium, and the associations were driven by CYP2R1-rs10741657 and rs10766197, and by GC-rs4588 and rs842999. Genetic risk score analysis showed that carriers with no risk alleles of CYP2R1-rs10741657 and rs10766197, and/or GC rs4588 and rs842999 had significantly higher serum 25(OH)D concentrations compared to carriers of all risk alleles. To conclude, our results provide supporting evidence that common polymorphisms in GC and CYP2R1 are associated with serum 25(OH)D concentrations in the Caucasian population and that certain haplotypes may predispose to lower 25(OH)D concentrations in late summer in Denmark.

Determinants of serum T4 and T3 at the time of diagnosis in nosological types of thyrotoxicosis: a population-based study

OBJECTIVE

To characterize thyroid hormone levels at the time of diagnosis in the nosological types of thyrotoxicosis diagnosed in the population and to analyze determinants for serum thyroxine (T4) and tri-iodothyronine (T3).

DESIGN

Population-based study of thyrotoxicosis at disease onset.

METHODS

In the period 1997-2000, we prospectively identified all patients diagnosed with incident primary overt thyrotoxicosis in a Danish population cohort and classified patients into ten well-defined nosological types of disease (n=1082). Untreated levels of serum T3, T4, and T3:T4 ratio were compared and related to sex, age, level of iodine deficiency, smoking status, alcohol intake, iodine supplement use, co-morbidity, and TSH receptor antibodies (TRAbs) in multivariate models.

RESULTS

Graves' disease (GD) patients had much higher levels of T3 and higher T3:T4 ratio at diagnosis compared with other thyrotoxic patients, but with a profound negative association between hormone levels and age. In GD, patients diagnosed in the area with more severe iodine deficiency had lower levels of T3 and T4. TRAb-negative GD patients had biochemically mild thyrotoxicosis. Higher age was also associated with lower degree of biochemical thyrotoxicosis in nodular toxic goiter. We found no association between serum T3 and T4 and sex, smoking habits, iodine supplements, alcohol intake, or co-morbidity in any type of thyrotoxicosis.

CONCLUSIONS

The study gives new insight into the hormonal presentation of thyrotoxicosis and showed that young age, positive TRAb levels, but also residency in the area with higher iodine intake was positively associated with biochemical disruption in GD.

Serum selenium is low in newly diagnosed Graves' disease: a population-based study

CONTEXT

Selenium deficiency may play an important role in the initiation and progression of autoimmune thyroid disease.

OBJECTIVE

To compare serum selenium (s-Se) values in patients with newly diagnosed autoimmune thyroid disease and controls from the Danish population.

DESIGN AND SETTINGS

S-Se was measured in triplicate by a fluorimetric method.

PARTICIPANTS

Patients with newly diagnosed Graves' disease (GD) (n = 97) or autoimmune overt hypothyroidism (AIH) (n = 96), euthyroid subjects with high serum levels of thyroid peroxidase antibody (TPO-Ab) (TPO-Ab > 1500 U/ml, n = 92) and random controls (n = 830).

MAIN OUTCOME MEASURE

Differences in s-Se values.

RESULTS

S-Se was lower in patients with GD than in controls (mean (SD), GD: 89·9 μg/l (18·4); controls: 98·8 μg/l (19·7), P < 0·01). This was confirmed in a multivariate logistic regression model adjusting for age, sex, mineral supplements, smoking, geographical region and time of sampling (P < 0·01). In a linear model, s-Se was similar in patients with AIH (mean (SD): 98·4 μg/l (24·9)) and in controls (P = 0·86). In the multivariate model however, s-Se was marginally lower in patients with AIH compared to controls (P = 0·04). There was no significant difference in s-Se between euthyroid participants with high TPO-Ab and random controls (linear: P = 0·97; multivariate: P = 0·27).

CONCLUSION

Patients with newly diagnosed GD and AIH had significantly lower s-Se compared with random controls. Our observation supports the postulated link between inadequate selenium supply and overt autoimmune thyroid disease, especially GD.

Graves' hyperthyroidism and moderate alcohol consumption: evidence for disease prevention

BACKGROUND

We recently demonstrated that moderate alcohol consumption is associated with a considerable reduction in the risk of autoimmune hypothyroidism, similar to findings in other autoimmune diseases such as systemic lupus erythematosus and rheumatoid arthritis. We aimed to study a possible association between alcohol intake and autoimmune Graves' hyperthyroidism.

DESIGN

This is a population-based, case-control study.

METHODS

In a well-defined Danish population (2,027,208 person-years of observation), we prospectively identified patients with new overt thyroid dysfunction and studied 272 patients with Graves' hyperthyroidism. For each patient, we recruited four age-gender-region-matched controls with normal thyroid function (n = 1088).

MEASUREMENTS

Participants gave detailed information on current and previous alcohol intake as well as other factors to be used for analyses. The association between alcohol intake and development of hyperthyroidism was analysed in conditional multivariate Cox regression models.

RESULTS

Graves' patients had a lower reported alcohol consumption than controls (median units of alcohol (12 g) per week: 2 vs 4, P < 0·001). In a multivariate regression model, alcohol consumption was associated with a dose-dependent reduction in risk for development of overt Graves' hyperthyroidism. Odds ratios (95% confidence interval) compared with the reference group with a recent (last year) consumption of 1-2 units of alcohol per week were as follows: 0 units/week 1·73 (1·17-2·56), 3-10 units/week 0·56 (0·39-0·79), 11-20 units/week 0·37 (0·21-0·65), ≥21 units/week 0·22 (0·08-0·60). Similar results were found for maximum previous alcohol consumption during a calendar year. No interaction was found with the type of alcohol consumed (wine vs beer), smoking habit, age, gender or region of inhabitancy.

CONCLUSIONS

Moderate alcohol consumption is associated with a considerable reduction in the risk of Graves' disease with hyperthyroidism--irrespective of age and gender. Autoimmune thyroid disease seems to be much more dependent on environmental factors than hitherto anticipated.

Smoking cessation is followed by a sharp but transient rise in the incidence of overt autoimmune hypothyroidism - a population-based, case-control study

BACKGROUND

Current smoking is associated with a low prevalence of thyroid autoantibodies. On the other hand, smoking withdrawal enhances thyroid autoantibody level and may be a risk factor for the development of hypothyroidism. The aim of this study was to assess the association between smoking habits (smoking cessation in particular) and development of autoimmune hypothyroidism.

DESIGN

Population-based, case-control study.

PARTICIPANTS

Cases (n = 140) newly diagnosed with primary autoimmune overt hypothyroidism were identified prospectively by population monitoring (2,027,208 person-years of observation) of all thyroid function tests performed in the two well-defined geographical areas. Individually, age-, sex- and region-matched euthyroid controls (n = 560) were simultaneously included from the same population.

MEASUREMENTS

Participants gave details on smoking habits including smoking withdrawal and other lifestyle factors. Smoking habits were verified by measuring urinary cotinine (a nicotine metabolite).

RESULTS

Incident hypothyroidism was very common in people who had recently stopped smoking: OR vs never smokers (95%-CI); quit smoking <1 years, 7·36 (2·27-23·9); 1-2 years, 6·34 (2·59-15·3); 3-10 years, 0·75 (0·30-1·87); >10 years, 0·76 (0·38-1·51). Results were consistent in both sexes and irrespective of age. Within two years after smoking cessation, the percentage of hypothyroid cases attributable to cessation of smoking was 85%. The current smoking was not associated with altered risk of developing overt hypothyroidism [OR, 0·92 (0·57-1·48)].

CONCLUSIONS

The risk of having overt autoimmune hypothyroidism diagnosed is more than 6-fold increased the first 2 years after cessation of smoking. Clearly, smoking cessation is vital to prevent death and severe disease. However, awareness of hypothyroidism should be high in people who have recently quit smoking, and virtually any complaint should lead to thyroid function testing.

Moderate alcohol consumption may protect against overt autoimmune hypothyroidism: a population-based case-control study

OBJECTIVE

Alcohol consumption is an important protective risk factor for many autoimmune diseases. We wished to study the association between alcohol consumption and autoimmune hypothyroidism.

DESIGN

Population-based, case-control study, 1997-2001, Denmark.

METHODS

Patients with newly diagnosed autoimmune overt hypothyroidism (n=140) were prospectively identified in a population (2 027 208 person-years of observation), and their matched controls with normal thyroid function (n=560) were recruited simultaneously from the same population. Participants gave information on alcohol intake, smoking, previous diseases, education, and family history of hypothyroidism. The association between alcohol intake and development of hypothyroidism was analyzed in conditional regression models.

RESULTS

Hypothyroid cases had reported a lower alcohol consumption than controls (median units of alcohol (12 g) per week: 3 vs 5, P=0.002). In a multivariate regression model, alcohol consumption was associated with a reduction in risk for development of overt autoimmune hypothyroidism. Odds ratios (95% confidence interval) compared with the reference group with a recent (last year) consumption of 1-10 units of alcohol per week were as follows: 0 units/week, 1.98 (1.21-3.33); 11-20 units/week, 0.41 (0.20-0.83); and ≥21 units/week, 0.90 (0.41-2.00). Similar results were found for maximum previous alcohol consumption during a calendar year. No interaction was found with type of alcohol consumed (wine vs beer), sex, or region of inhabitancy.

CONCLUSIONS

Alcohol consumption seems to confer considerable protection against development of overt autoimmune hypothyroidism irrespective of sex and type of alcohol consumed.

[Iodine fortification of salt and thyroid disease in Denmark]

Until 2000 Denmark was iodine deficient with moderate deficiency in the western part and mild deficiency in the eastern part. The occurrence of goitre and autonomous hyperthyroidism was high, and pregnancy was associated with a reduction in thyroid function. After cautious mandatory iodization of household salt and salt used for bread production, the iodine intake in Denmark is now low normal. The DanThyr monitoring has shown a transient increase in hyperthyroidism followed by a decrease, and goitre is becoming less common. Hypothyroidism has become more common, and this has to be followed.

Stagnation in body mass index in Denmark from 1997/1998 to 2004/2005, but with geographical diversity

INTRODUCTION

We analyzed the trend in body mass index (BMI) as well as in the prevalence of overweight and obesity among Danish adults, mainly women, from 1997/1998 to 2004/2005 and evaluated any regional differences.

MATERIAL AND METHODS

Data were drawn from two cross-sectional population-based studies conducted in parallel in Aalborg and Copenhagen from 1997/1998 and 2004/2005. Height and weight were measured in a total of 7,487 participants in the two cohorts.

RESULTS

In the total cohort, we found no significant difference in BMI from 1997/1998 to 2004/2005 (p = 0.828). There was an increase in BMI in Aalborg of 0.32 (p = 0.030), while in Copenhagen we observed a statistically significant decrease in BMI of 0.30 (p = 0.017). The difference in change over time in BMI between the two regions was significant (p = 0.002). Also the difference in the trend in prevalence of overweight and obesity was statistically significant between the two cities (p = 0.010).

CONCLUSION

Our results indicate that the obesity epidemic is leveling off - at least among women - and that it may even be receding in Copenhagen. Nevertheless, the absolute average BMI values and the prevalence of overweight and obesity in both cities are high which underlines the need for further initiatives to prevent obesity-related health risks in the future.

FUNDING

The DanThyr studies were supported by funding from the Tømmerhandler Vilhelm Bang Foundation, the Copenhagen Corporation Research Foundation, the 1991 Pharmacy Foundation, the Danish Medical Foundation, the Health Insurance Foundation, the Agnes and Knut Mørk Foundation, the Wedel Wedelsborg Foundation, the Ortho-Clinical Foundation and BRAHMS Diagnostica.

TRIAL REGISTRATION

not relevant.

Intake of micronutrients among Danish adult users and non-users of dietary supplements

Objectives

To evaluate the intake of micronutrients from the diet and from supplements in users and non-users of dietary supplements, respectively, in a representative sample of the Danish adult population. A specific objective was to identify the determinants of supplement use.

Design

A cross-sectional representative national study of the intake of vitamins and minerals from the diet and from dietary supplements.

Method

The Danish National Survey of Dietary Habits and Physical Activity, 2000–2004. Participants (n=4,479; 53% females) aged 18–75 years gave information about the use of dietary supplements in a personal interview. The quantification of the micronutrient contribution from supplements was estimated from a generic supplement constructed from data on household purchases. Nutrient intakes from the diet were obtained from a self-administered 7-day pre-coded dietary record. Median intakes of total nutrients from the diets of users and non-users of supplements were analysed using the Wilcoxon rank-sum test.

Results

Sixty percent of females and 51% of males were users of supplements. With the exception of vitamin D, the intake of micronutrients from the diet was adequate at the group level for all age and gender groups. Among females in the age group 18–49 years, the micronutrient intake from the diet was significantly higher compared with the non-users of dietary supplements. The use of dietary supplements increased with age and with ‘intention to eat healthy.’

Conclusion

Intake of micronutrients from the diet alone was considered adequate for both users and non-users of dietary supplements. Younger females who were supplement users had a more micronutrient-dense diet compared to non-users.

Doubling in the use of thyroid hormone replacement therapy in Denmark: association to iodization of salt?

Iodization of salt is an effective strategy to prevent iodine deficiency disorders. Recent studies, however, indicate that increasing the iodine intake in a population may give rise to an increased incidence of hypothyroidism, but the association has not been fully clarified. In Denmark, iodization of salt was initiated in 1998 because of mild-to-moderate iodine deficiency. The aim of this study was to evaluate the effect of the raised iodine intake on the nationwide incident use of thyroid hormone replacement therapy (levothyroxine) to treat hypothyroidism. Data on all use of levothyroxine was extracted from the Register of Medicinal Product Statistics during the period 1995-2009 and linked to other nationwide registers by use of the Danish identification number. Persons with previous thyroid surgery were excluded. In the studied period 71,565 incident users were identified. The incidence rate increased 75% in the moderately iodine deficient region (72.2 incident users/100,000 person-years in 1997 to 126.6 in 2008) and 87% in the mildly deficient region (86.9-162.9). When stratified by sex and age-group (00-39, 40-64, 65+) the largest relative increase was seen among women in the youngest age-group, where more than a doubling was seen. The mechanisms behind the increase may be a result of iodine-induced hypothyroidism, although a higher diagnostic activity with regard to thyroid dysfunction and intensified treatment of subclinical hypothyroidism may also play a role. Our findings stress the need for caution when initiating iodine fortification programs to keep the intake within the optimal range, and the need for continuous monitoring.

Epidemiology of subtypes of hyperthyroidism in Denmark: a population-based study

OBJECTIVE

Few population-based studies have described the epidemiology of subtypes of hyperthyroidism.

DESIGN

A prospective population-based study, monitoring two well-defined Danish cohorts in Aalborg with moderate iodine deficiency (n=311 102) and Copenhagen with only mild iodine deficiency (n=227 632).

METHODS

A laboratory monitoring system identified subjects with thyroid function tests suggesting overt hyperthyroidism (low s-TSH combined with high s-thyroxine or s-triiodothyronine). For all subjects, we collected information on medical history, thyroid scintigraphy and thyroid hormone receptor antibody (TRAb) measurement. Information was used to disprove or verify primary overt hyperthyroidism and to subclassify hyperthyroidism into nosological disorders.

RESULTS

From 1997 to 2000 (2 027 208 person-years of observation), we verified 1682 new cases of overt hyperthyroidism. The overall standardized incidence rate (SIR) per 100 000 person-years was 81.6, and was higher in Aalborg compared with Copenhagen (96.7 vs 60.0, P<0.001), giving an SIR ratio (SIRR (95% confidence interval (CI))) between moderate versus mild iodine-deficient areas of 1.6 (1.4-1.8). Nosological types of hyperthyroidism (percentage/SIRR (95% CI)): multinodular toxic goitre (MNTG) 44.1%/1.9 (1.6-2.2), Graves' disease (GD) 37.6%/1.2 (0.99-1.4), solitary toxic adenoma (STA) 5.7%/2.4 (1.3-3.5), 'mixed type' hyperthyroidism (TRAb-positive, scintigraphicly multinodular) 5.4%/6.0 (3.0-12), subacute thyroiditis 2.3%/0.9 (0.4-1.4), postpartum thyroid dysfunction 2.2%/1.6 (0.8-3.0), amiodarone-associated hyperthyroidism 0.8%/7.1 (1.1-65), hyperthyroidism after thyroid radiation 0.7%/12.3 (0.8-50), lithium-associated hyperthyroidism 0.7%/0.97 (0.4-4.8) and hyperthyroidism caused by various other factors 0.7%. Lifetime risk for overt hyperthyroidism was 10.5%/6.5%/2.4% (females/all/males).

CONCLUSION

Hyperthyroidism was common in Denmark with MNTG and GD as dominating entities. The higher incidence of hyperthyroidism in the most iodine-deficient region was caused by higher frequency of MNTG, 'mixed-type', STA and amiodarone-associated hyperthyroidism.

Selenium status, thyroid volume, and multiple nodule formation in an area with mild iodine deficiency

OBJECTIVE

The objective was to study the associations between serum selenium concentration and thyroid volume, as well as the association between serum selenium concentration and risk for an enlarged thyroid gland in an area with mild iodine deficiency before and after iodine fortification was introduced. Another objective was to examine the association between serum selenium concentration and prevalence of thyroid nodules.

DESIGN

Cross-sectional study.

METHODS

We studied participants of two similar cross-sectional studies carried out before (1997-1998, n=405) and after (2004-2005, n=400) introduction of iodine fortification. Serum selenium concentration and urinary iodine were measured, and the thyroid gland was examined by ultrasonography in the same subjects. Associations between serum selenium concentration and thyroid parameters were examined in multiple linear regression models or logistic regression models.

RESULTS

Serum selenium concentration was found to be significantly, negatively associated with thyroid volume (P=0.006), and a low selenium status significantly increased the risk for thyroid enlargement (P=0.007). Furthermore, low serum selenium status had a tendency to increase the risk for development of multiple nodules (P=0.087).

CONCLUSIONS

Low serum selenium concentration was associated with a larger thyroid volume and a higher prevalence of thyroid enlargement.

Salt content in canteen and fast food meals in Denmark

Background

A high salt (=NaCl) intake is associated with high blood pressure, and knowledge of salt content in food and meals is important, if the salt intake has to be decreased in the general population.

Objective

To determine the salt content in worksite canteen meals and fast food.

Design

For the first part of this study, 180 canteen meals were collected from a total of 15 worksites with in-house catering facilities. Duplicate portions of a lunch meal were collected from 12 randomly selected employees at each canteen on two non-consecutive days. For the second part of the study, a total of 250 fast food samples were collected from 52 retail places representing both city (Aarhus) and provincial towns. The canteen meals and fast food samples were analyzed for chloride by potentiometric titration with silver nitrate solution, and the salt content was estimated.

Results

The salt content in lunch meals in worksite canteens were 3.8±1.8 g per meal and 14.7±5.1 g per 10 MJ for men (n=109), and 2.8±1.2 g per meal and 14.4±6.2 g per 10 MJ for women (n=71). Salt content in fast food ranged from 11.8±2.5 g per 10 MJ (burgers) to 16.3±4.4 g per 10 MJ (sausages) with a mean content of 13.8±3.8 g per 10 MJ.

Conclusion

Salt content in both fast food and in worksite canteen meals is high and should be decreased.

Iodine intake as a determinant of thyroid disorders in populations

Depending on the availability of iodine, the thyroid gland is able to enhance or limit the use of iodine for thyroid hormone production. When compensation fails, as in severely iodine-deficient populations, hypothyroidism and developmental brain damage will be the dominating disorders. This is, out of all comparison, the most serious association between disease and the level of iodine intake in a population. In less severe iodine deficiency, the normal thyroid gland is able to adapt and keep thyroid hormone production within the normal range. However, the prolonged thyroid hyperactivity associated with such adaptation leads to thyroid growth, and during follicular cell proliferation there is a tendency to mutations leading to multifocal autonomous growth and function. In populations with mild and moderate iodine deficiency, such multifocal autonomous thyroid function is a common cause of hyperthyroidism in elderly people, and the prevalence of thyroid enlargement and nodularity is high. The average serum TSH tends to decrease with age in such populations caused by the high frequency of autonomous thyroid hormone production. On the other hand, epidemiological studies have shown that hypothyroidism is more prevalent in populations with a high iodine intake. Probably, this is also a complication to thyroid adaptation to iodine intake. Many thyroid processes are inhibited when iodine intake becomes high, and the frequency of apoptosis of follicular cells becomes higher. Abnormal inhibition of thyroid function by high levels of iodine is especially common in people affected by thyroid autoimmunity (Hashimoto's thyroiditis). In populations with high iodine intake, the average serum thyroid-stimulating hormone (TSH) tends to increase with age. This phenomenon is especially pronounced in Caucasian populations with a genetically determined high tendency to thyroid autoimmunity. A small tendency to higher serum TSH may be observed already when iodine intake is brought from mildly deficient to adequate, but there is at present no evidence that slightly elevated serum TSH in elderly people leads to an increase in morbidity and mortality.

CONCLUSION

Even minor differences in iodine intake between populations are associated with differences in the occurrence of thyroid disorders. Both iodine intake levels below and above the recommended interval are associated with an increase in the risk of disease in the population. Optimally, iodine intake of a population should be kept within a relatively narrow interval where iodine deficiency disorders are prevented, but not higher. Monitoring and adjusting of iodine intake in a population is an important part of preventive medicine.

Treatment of fibromyalgia at the Maharishi Ayurveda Health Centre in Norway. A six-month follow-up study

BACKGROUND

Treatments offered at the Maharishi Ayurveda Health Centre in Norway are based on Maharishi Vedic medicine, which is also known as Maharishi Ayurveda. It is a consciousness based revival of the ancient Ayurvedic medicine tradition in India and is established by Maharishi Mahesh Yogi, the founder of the Transcendental Meditation (TM) technique.

OBJECTIVE

To conduct a pilot study of the effect of the treatment program at the Health Centre on fibromyalgia patients.

METHODS

Thirty-one women with diagnosed fibromyalgia received an individually designed Maharishi Vedic physiological purification therapy. All subjects received personal advice on diet based on Ayurvedic principles, including a novel approach to food into-lerance, and daily routines. In addition they were offered instruction in TM (for stress and pain management and personal development) (four subjects started), and recommended Ayurvedic herbal food products for home treatment.

MAIN OUTCOME MEASURES

A modified Fibromyalgia Impact Questionnaire included a visual analogue scale for each of the seven outcomes: working ability, generalised pain, tiredness, stiffness, tiredness on arising, anxiety and depression. Pre-treatment scores were compared with scores at six-month follow-up for levels of statistical significance.

RESULTS

Twenty-eight subjects (90%) completed the follow-up. The outcome measures were reduced by 25 to 46% by the study's endpoint: working ability (p<0.002), pain (p<0.001), tiredness (p<0.001), morning tiredness (p<0.001), stiffness (p<0.005), anxiety (p<0.136), and depression (p<0.001). A group of five excellent responders including all four participants who started to practise TM, had almost no symptoms by the endpoint. Compared to the non-meditating control group the TM-subgroup showed statistically significant improvements for all outcome measures except depression.

CONCLUSIONS

In this pilot study fibromyalgia patients undergoing treatment at Maharishi Ayurveda Health Centre in Norway showed significant improvements six months post treatment. Because fibromyalgia is considered a treatment-resistant condition, these encouraging results warrant further research.

Thyroid peroxidase and thyroglobulin auto-antibodies in patients with newly diagnosed overt hypothyroidism

OBJECTIVES

Thyroid autoimmunity is a major cause for hypothyroidism. We describe thyroid auto-antibodies in patients with various nosological subtypes of hypothyroidism identified in a population study.

DESIGN

Population-based follow-up study identifying all new cases of hypothyroidism in an open cohort.

METHODS

We established a monitoring system, and identified all new cases with primary overt hypothyroidism (n = 685) in a 4 year period in a well-defined population cohort (2,027,208 person-years of observation). Patients were sub-classified into: spontaneous hypothyroidism, presumably of autoimmune origin (n = 578); non-spontaneous hypothyroidism (associated with medication, delivery, neck-irradiation or subacute thyroiditis, n = 97); and congenital hypothyroidism (n = 10). A total of 186 adult patients (61% of those invited) underwent thyroid ultrasonography and measurements of antibodies against thyroid peroxidase (TPOAb) and thyroglobulin (TgAb).

RESULTS

In spontaneously hypothyroid patients: >99% were antibody-positive (TPOAb or TgAb), TPOAb were more often measurable than TgAb (95.9 vs. 80.7%, p < 0.001). A statistically significant but modest correlation was observed between the two antibodies (Pearson's r2 = 0.11, p < 0.001). In a multivariate regression model both TPOAb and TgAb were positively associated with thyroid enlargement (p < 0.001), whereas no association was found with sex, age, iodine deficiency level or serum TSH level. We found no differences in patient characteristics between those who mainly developed TPOAb vs. those who preferentially harboured TgAb.

CONCLUSIONS

Autoimmunity played a dominant role in practically all patients classified as spontaneously hypothyroid. Thyroid enlargement was associated with high levels of TPOAb and TgAb. We found no clue to why some spontaneously hypothyroid patients predominantly developed TPOAb whereas others mainly generated TgAb.

Serum selenium and selenoprotein P status in adult Danes - 8-year followup

Selenium is an essential micronutrient important to human health. The main objective of this study is to describe serum selenium and selenoprotein P status in two samples of the Danish population. In addition, the influence of various factors potentially associated with selenium status was investigated. Blood samples from a total of 817 randomly selected subjects from two cities in Denmark were analyzed. Half of the samples were collected in 1997-1998 and the other half in 2004-2005. Samples from women aged 18-22, 40-45 and 60-65 years, and men aged 60-65 years were selected for this study. All subjects had filled in a food frequency questionnaire (FFQ) and a questionnaire with information about smoking habits, alcohol consumption and exercise habits. Mean serum selenium level was 98.7+/-19.8microg/L and median selenoprotein P level was 2.72 (2.18-3.49)mg/L. Serum selenium and selenoprotein P increased with age, and selenoprotein P was higher in men than in women. Serum selenium levels decreased by 5% on average from 1997-98 to 2004-05 (P<0.001), whereas selenoprotein P level increased (P<0.001). The intake of fish correlated weakly with serum selenium level (r=0.14, P<0.001) but not with selenoprotein P level. Smoking status, alcohol intake, exercise habits, BMI and medicine use did not influence selenium status. It is concluded that selenium status in this Danish population is at an acceptable level. No major groups with regard to age, sex or lifestyle factors could be identified as being in risk for selenium deficiency.

Smoking is negatively associated with the presence of thyroglobulin autoantibody and to a lesser degree with thyroid peroxidase autoantibody in serum: a population study

BACKGROUND

Autoimmune thyroid diseases are common and the prevalence of circulating thyroid antibodies (thyroid peroxidase antibody, TPO-Ab and thyroglobulin antibody, Tg-Ab) is high in the population. The knowledge of a possible association between lifestyle factors and circulating thyroid antibodies is limited.

AIM

To evaluate the correlation between smoking habits and the presence of circulating TPO-Ab and Tg-Ab.

MATERIAL AND METHODS

In a cross-sectional comparative population study performed in two areas of Denmark with moderate and mild iodine deficiency, 4649 randomly selected subjects from the population in some predefined age groups between 18 and 65 years were examined. Blood tests were analysed for TPO-Ab and Tg-Ab using assays based on the RIA technique. The participants answered questionnaires, were clinically examined and blood and urine samples collected.

RESULTS

Data were analysed in multivariate logistic regression models. There was a negative association between smoking and the presence of thyroid autoantibodies in serum. This association was observed for the presence of TPO-Ab and/or Tg-Ab, TPO-Ab (without respect to Tg-Ab status), Tg-Ab (without respect to TPO-Ab status) and both antibodies together. The association between smoking and thyroid autoantibodies was stronger for Tg-Ab than for TPO-Ab. There was no association between smoking and TPO-Ab measured alone or between smoking and TPO-Ab when Tg-Ab was included in the model as an explanatory variable.

CONCLUSION

Smoking was negatively associated with the presence of thyroid autoantibodies with the strongest association between smoking and Tg-Ab. The study design precludes any conclusions as to the cause of the negative association between smoking thyroid autoantibodies.

An increased incidence of overt hypothyroidism after iodine fortification of salt in Denmark: a prospective population study

CONTEXT

Iodine fortification (IF) of salt was introduced in Denmark in 1998. Little is known about the effect of a minor increase in iodine intake on the incidence of hypothyroidism. We prospectively identified all new cases of overt hypothyroidism in two areas of Denmark before and for the first 7 yr after IF had been introduced.

METHODS

A computer-based register was used to identify continuously all new cases of overt hypothyroidism in two subcohorts with previous moderate and mild iodine deficiency (ID), respectively (Aalborg, n = 310,124, urinary iodine = 45 microg/liter; and Copenhagen, n = 225,707, urinary iodine = 61 microg/liter). Data were obtained 1) before IF (1997-1998), 2) during voluntary IF (1999-2000), 3) during early (2001-2002) and 4) during late (2003-2005) period with mandatory IF.

RESULTS

The overall incidence rate of hypothyroidism increased during the study period: baseline, 38.3/100,000.yr; voluntary IF, 43.7 (not significant vs. baseline); early mandatory IF, 48.7 [vs. baseline, rate ratio (RR) = 1.27; 95% confidence interval (CI) = 1.10-1.47]; and late mandatory IF, 47.2 (vs. baseline, RR = 1.23; 95% CI = 1.07-1.42). There was a geographic difference because hypothyroidism increased only in the area with previous moderate ID: Aalborg, late mandatory IF vs. baseline, 40.3/29.7 (RR = 1.11; 95% CI = 1.11-1.66); Copenhagen, 56.7/51.6 (RR = 1.10; 95% CI = 0.90-1.34). The increase occurred in young and middle-aged adults.

CONCLUSION

Even a cautious iodization of salt was accompanied by a moderate increase in the incidence rate of overt hypothyroidism. This occurred primarily in young and middle-aged subjects with previous moderate ID.

Characteristics of misreporters of dietary intake and physical activity

Objective

To characterise misreporters of energy intake (EI) and energy expenditure (EE).

Design

Cross-sectional study, using a validated position and motion instrument, ActiReg®, as the reference method to study misreporters of EI and of EE. EI was measured using a dietary record and EE using a physical activity questionnaire (PAQ). Misreporters were defined as subjects outside the 95% confidence limits of agreement between EI or EE reported/EE measured.

Setting

Free-living Danish volunteers.

Subjects

One hundred and thirty-eight volunteers aged between 20 and 59 years.

Results

Body mass index, smoking, ‘try to eat healthily’ and worries about weight were related to degree of under-reported EI. The percentage energy from added sugar was lowest (P < 0.001) and the percentage energy from protein (P < 0.001) highest in under-reporters compared with acceptable reporters. Subjects who reported being very physically active at work or in leisure time reported a higher EE than measured EE compared with less physically active subjects (P < 0.05). Likewise, subjects who regard themselves as fit or very fit reported a higher EE than subjects who regard themselves as moderately fit (P < 0.05). Possible over-reporters reported less time as very light activity (P = 0.007), more time as moderate activity (P = 0.01) and more time as vigorous activity (P = 0.02) than acceptable reporters.

Conclusions

Under-reporting of EI should always be taken into consideration; however, only a few characteristics of under-reporters are consistent among studies. Misreporting of EI was more prevalent than misreporting of EE. The level of physical activity more than the time spent involved in various activities was misreported.

Increase in incidence of hyperthyroidism predominantly occurs in young people after iodine fortification of salt in Denmark

CONTEXT

To prevent goiter and nodular hyperthyroidism, iodine fortification (IF) of salt was introduced in Denmark in 1998. We prospectively registered all new cases of overt hyperthyroidism in two areas of Denmark before and for the first 6 yr after iodine fortification.

METHODS

We used a computer-based register of all new cases of hyperthyroidism in two population subcohorts with moderate iodine deficiency (Aalborg, n = 310,124) and mild iodine deficiency (Copenhagen, n = 225,707), respectively. Data were obtained 1) before IF (1997-1998); 2) during voluntary IF (1999-2000); 3) during the early (2001-2002) period of mandatory IF; and 4) during the late (2003-2004) period with mandatory IF.

RESULTS

The overall incidence rate of hyperthyroidism increased [baseline, 102.8/100,000/year; voluntary IF, 122.8; early mandatory IF, 140.7; late mandatory IF, 138.7 (P for trend <0.001)]. Hyperthyroidism increased in both sexes (P < 0.001) and in all age groups: 0-19, 20-39, 40-59, and 60+ yr (P for trend <0.001). The increase was relatively highest in young adults aged 20-39 yr: late mandatory IF (percent increase from baseline), age 20-39, 160%, P < 0.001; age 40-59, 29%, P < 0.01; age 60+ yr, 13%, P = not significant.

CONCLUSION

Even a cautious iodization of salt results in an increase in the incidence rate of hyperthyroidism. Contrary to current concepts, many of the new cases were observed in young subjects, and are presumably of autoimmune origin. Furthermore, monitoring is expected to show a decrease in the number of elderly subjects suffering from nodular hyperthyroidism.

[Selenium and health]

Selenium is an essential micronutrient. The average selenium intake in Danish adults is close to the recommended level of 40-50 mg/day. There is no scientific documentation showing that an increased selenium intake will result in disease prevention. However, a preventive effect on some cancers and hearth disease cannot be ruled out. Fortification of foods via increased selenium content in fertilizers is a possible way of increasing selenium intake. The tolerable upper intake level of 60 mg/day in children 1-3 years old must not be exceeded, which makes fortification difficult.

Lack of association between thyroid autoantibodies and parity in a population study argues against microchimerism as a trigger of thyroid autoimmunity

BACKGROUND

Thyroid autoimmunity is more common in females than in males. One possible explanation for this female preponderance may be the effect of oestrogens on the immune system. It has also been suggested that foetal microchimerism involving transfer of foetal cells into maternal tissue during pregnancy may play an important role.

OBJECTIVE

We investigated the association between the presence of circulating thyroid autoantibodies and previous pregnancy, parity and the use of oral contraceptives (OCs) and hormone replacement therapy (HRT) in a population cohort.

METHODS

We examined 3712 women randomly selected from the general population. Serum was analysed for thyroid peroxidase antibody (TPO-Ab) and thyroglobulin antibody (Tg-Ab) using assays based on an RIA technique (DYNO test). Data were analysed in logistic regression models to adjust for possible confounders. Women previously treated for thyroid disease or with pregnancy within 1 year prior to the study were excluded from the analyses.

RESULTS

In both univariate and multivariate models and whether the presence of TPO-Ab and Tg-Ab was investigated alone or in combination, findings were negative with respect to an association between circulating thyroid antibodies and previous pregnancy, number of pregnancies, parity and previous abortion. There was no association between thyroid autoantibodies and use of OCs. Women aged 60-65 years receiving HRT now or previously had a lower prevalence of Tg-Ab (univariate, P = 0.01; multivariate, P = 0.02). No such association was observed between HRT and TPO-Ab.

CONCLUSION

In this population study there was no association between previous pregnancy, parity and thyroid antibodies, which argues against the role of microchimerism as a trigger of thyroid autoimmunity. Exogenous oestrogens may reduce aspects of autoimmunity.

Epidemiology of subtypes of hypothyroidism in Denmark

OBJECTIVE

Studies of hypothyroidism are often based on referred patients, and limited information is available on the incidence rates of subtypes of hypothyroidism in the general population. We therefore studied incidences of subtypes of primary, overt hypothyroidism in a Danish population cohort and compared incidences in two subcohorts with different levels of iodine intake.

DESIGN

A prospective population-based study, monitoring a well-defined cohort representative of the Danish population.

METHODS

The Danish Investigation of Iodine Intake and Thyroid Diseases registry of hyper- and hypothyroidism was established as part of the monitoring of the iodine fortification of salt in Denmark. A computer-based system linked to laboratory databases identified all patients diagnosed with new, biochemically overt hypothyroidism in populations living in Aalborg (moderate iodine deficiency, n = 311,102) and Copenhagen (mild iodine deficiency, n = 227,632). We subsequently evaluated all identified patients to verify incident thyroid disease, and subclassified hypothyroidism into nosological types.

RESULTS

During a 4-year period (2,027,208 person-years) 685 new cases of overt hypothyroidism were diagnosed in the cohort; the incidence rate was 32.8 per 100,000 person-years (standardised to the Danish population). Nosological types of hypothyroidism were: spontaneous (presumably autoimmune) 84.4%, post-partum 4.7%, amiodarone-associated 4.0%, subacute thyroiditis 1.8%, previous radiation or surgery 1.8%, congenital 1.6% and lithium-associated 1.6%. Crude incidence rates were 29.0 around Aalborg and 40.6 in an area of Copenhagen. The higher incidence rate of hypothyroidism in the area with higher iodine intake was caused solely by more cases of spontaneous (presumably autoimmune) hypothyroidism, whereas the incidence of non-spontaneous hypothyroidism (all types combined) was significantly lower in the area with higher iodine intake.

CONCLUSION

In a population-based study we observed a higher incidence of hypothyroidism with higher iodine intake. This was due solely to the entity of spontaneous hypothyroidism. The occurrence of overt hypothyroidism was relatively low in Denmark.

A population study of the association between thyroid autoantibodies in serum and abnormalities in thyroid function and structure

OBJECTIVE

Patients with autoimmune overt hypothyroidism may present with goitrous Hashimoto's disease or autoimmune atrophic thyroiditis. Little is known about the prevalence of subclinical autoimmune hypothyroidism. The aims of this study were to evaluate the association between thyroid autoantibodies in serum and abnormalities in thyroid function and structure, and to study the thyroid volume in subjects with subclinical autoimmune hypothyroidism.

DESIGN

A population study including 4649 randomly selected subjects.

MEASUREMENTS

Blood tests were used to analyse for thyroid peroxidase autoantibodies (TPO-Ab), thyroglobulin autoantibodies (Tg-Ab), TSH, fT3 and fT4.

RESULTS

Thyroid volume was categorized as small (< 6.6 ml) in 4.7%, normal (6.6-14.9 ml) in 60.4% and large (> 14.9 ml) in 34.9% of participants. Thyroid nodules were found in 29.7%. Serum TSH was low (< 0.4 mIU/l) in 4.7%, normal (0.4-3.6) in 91.0% and high (> 3.6) in 4.3%. The prevalence rate of subclinical goitrous Hashimoto's disease was 0.62% and of subclinical autoimmune atrophic thyroiditis 0.24%. There was a strong association between large volume and autoantibodies, but only in subjects with elevated TSH (P < 0.001). An association between thyroid nodules and TPO-Ab in univariate analyses (P < 0.001) was due to confounding by sex and age (multivariate model, P = 0.23).

CONCLUSION

We identified a subgroup of the population with subclinical goitrous Hashimoto's disease and a smaller subgroup with subclinical autoimmune atrophic thyroiditis. This relationship between small and large thyroid volume in subclinical disease is opposite to that in overt disease, which may suggest that the period between development of a small volume with circulating autoantibodies and overt hypothyroidism is relatively short.

Evaluation of a semi-quantitative food frequency questionnaire to estimate iodine intake

OBJECTIVE

To evaluate a food frequency questionnaire (FFQ) used to assess the dietary intake of iodine.

DESIGN

The iodine intake determined by the FFQ was compared with 4-day dietary records and with iodine excretion in 24 h urine samples in a subgroup of participants in a cross-sectional study of iodine intake and thyroid diseases in Denmark. Furthermore, the intake of fish determined from the FFQ was compared with the intake of fish from a simple record kept for 3 months.

SUBJECTS

Women aged 25-30 y and 60-65 y.

RESULTS

Median iodine intake was similar when determined from the FFQ and from dietary records and the correlation between these measures was 0.52 (P < 0.001). Iodine intake was higher than iodine excretion (P < 0.001). The cross-check questions in the FFQ (for example the question 'How often did you get any kind of fish?') underestimated the intake. In contrast, the intake of a specific fish tended to be overestimated by the FFQ when compared with the 3 month record of fish intake.

CONCLUSION

The FFQ can be used to classify subjects into low and high iodine intake groups, but the level of iodine tends to be overestimated.

Folate intake, lifestyle factors, and homocysteine concentrations in younger and older women

BACKGROUND

An elevated total homocysteine (tHcy) concentration is considered to be an independent risk factor for cardiovascular diseases and has also been associated with an increased risk of neural tube defects.

OBJECTIVE

The objective of this study was to investigate folate intake, folate status, and the association between folate intake, other dietary and lifestyle factors, and tHcy concentrations in young and older women.

DESIGN

tHcy concentrations were measured in 290 young women aged 25-30 y and in 288 older women aged 60-65 y. All participants completed questionnaires about factors including lifestyle, health, and use of vitamin supplements. Red blood cell folate was measured in 204 of the participants. A subgroup of 258 participants completed dietary records.

RESULTS

Median tHcy was 7.6 micromol/L (range: 6.5-8.9) in the younger women and 9.4 micromol/L (7.7-11.1) in the older women. Folate intake from diet was 283 (224-348) and 268 (210-326) microg/d, respectively, in the 2 age groups. Folic acid intake from supplements (P: < 0.001 for the younger women and P: = 0.026 for the older women) and total folate intake (P: = 0.024 and P: = 0.079) were inversely associated with log tHcy in multiple linear regression analyses. Smoking status, coffee consumption, systolic blood pressure, and body mass index were positively associated and estrogen replacement therapy and tea consumption were inversely associated with log tHcy in some of the models.

CONCLUSIONS

According to the criteria used, between 1% and 36% of the women had suboptimal folate intake. Folic acid is a strong predictor of tHcy concentration; however, several dietary and other lifestyle factors seem to be important as well.