Association of triiodothyronine levels with future development of metabolic syndrome in euthyroid middle-aged subjects: a 6-year retrospective longitudinal study

Association between hypothyroidism and metabolic syndrome in Qinghai, China

Objective

To investigate the epidemiological characteristics of hypothyroidism in Qinghai Province, analyze its related influencing factors, establish the normal reference range of thyroid function, and explore the relationship between thyroid hormone (THs), thyroid stimulating hormone (TSH) and metabolic syndrome (MS) in Qinghai population within the normal range, so as to provide some scientific basis for the prevention and treatment of hypothyroidism in Qinghai Province.

Methods

A total of 2790 residents aged 18 and over from Qinghai were selected through stratified cluster random sampling. Data were collected via questionnaires, physical examinations, and laboratory tests.

Results

1. A total of 2628 eligible residents in Qinghai were included in this study, and the total prevalence of hypothyroidism was 30.25%, among which the prevalence of subclinical hypothyroidism was 29.22%, and the prevalence of clinical hypothyroidism was 1.03%. 2. The prevalence of hypothyroidism in women was significantly higher than that in men (36.69% vs 24.30%); smoking and drinking were risk factors for hypothyroidism. 3. In the excluded subjects, 1544 were abnormal thyroid ultrasound, abnormal thyroid function and/or positive thyroid autoantibodies, and the remaining 1084 were reference populations. According to the reference population data, the 95% reference ranges of TSH, FT4, FT3 were 0.43-5.51 mIU/L, 11.0-20.4 pmol/L, 3.63-5.73 pmol/L, respectively. 4. In the normal thyroid function population in Qinghai, MS and its related components were positively correlated with FT3 and FT4 levels, but not significantly correlated with TSH levels.

Conclusion

1. The prevalence of hypothyroidism in adults in Qinghai is relatively high, accounting for about one-thirtieth of the total population. Smoking and drinking have a certain impact on the incidence of hypothyroidism. 2. It provides a reference range for the diagnosis of thyroid diseases in Qinghai province, which is different from that of reagent suppliers, and has certain promotion significance in the western region. 3. MS and its related components are positively correlated with FT3 and FT4 levels, but not with TSH levels in people with normal thyroid function in Qinghai. Early thyroid function screening is of great significance for the prevention of MS.

Elevated thyroid stimulating hormone and metabolic syndrome risk in patients with first-episode and drug-naïve major depressive disorder: a large-scale cross-sectional study

BACKGROUND

Metabolic syndrome (MetS) is common in major depressive disorder (MDD), but its relationship with thyroid hormones remains unclear. We aimed to examine the association of thyroid hormones and MetS in first-episode drug-naïve (FEDN) MDD patients.

METHODS

We recruited 1718 unmedicated MDD patients in this cross-sectional study. MetS was defined based on the 2004 Chinese Diabetes Society Criteria. Serum thyroid hormones including free thyroxine (FT4), free triiodothyronine (FT3), thyroid-stimulating hormone (TSH), thyroid peroxidase antibodies (TPOAb), and anti-thyroglobulin (TGAb) were examined. We used the logistic regression model to determine risk factors for MetS and examined the performance of the regression model by using the Area Under the Curve (AUC). In addition, we performed the trend test to test whether the results were robust.

RESULTS

The prevalence of MetS in unmedicated MDD patients was 34.4%. MDD patients with MetS had higher levels of serum TSH, TGAb, and TPOAb (all P < 0.001). Concurrently, serum TSH levels were independent risk factors for MetS in MDD patients (OR:1.49, 95%CI: 1.40-1.58), which could also distinguish MDD patients with and without MetS (AUC was 0.77). Additionally, in the trend test, the results also indicated a similar trend when TSH was used as a categorical variable (P for trend < 0.001).

CONCLUSIONS

This study suggests that TSH levels were independent risk factors for MetS in FEDN MDD patients (OR:1.49). The examination of thyroid function may contribute to the early detection of MetS.

Predictability Of Metabolic Syndrome Diagnosed By Body Mass Index For Cardiovascular Risk In Older Patients Treated With Levothyroxine

Background

We investigated the prevalence and metabolic features of two definitions of metabolic syndrome (MS) between older patients with chronic thyroiditis treated with levothyroxine (LT4) and controls. We also assessed the ability of both criteria to predict cardiovascular (CV) risk.

Methods

This cross-sectional, retrospective study included individuals aged ≥60 years who attended a geriatric outpatient clinic between January 2015 and December 2018. The LT4 treatment group was classified as having high or low CV risk based on the Framingham score.

Results

This study enrolled 111 patients with chronic thyroiditis treated with LT4 and 131 patients without thyroid disease as the control group. The prevalence of MS according to the World Health Organization (WHO) criteria and American Association of Clinical (AACE) criteria was similar in the LT4 treatment (21.6% and 26.1%, respectively) and the control (30.5% and 34.4%, respectively) groups (p>0.05). While the prevalence of MS and CV risk did not differ significantly between the control and LT4 treatment groups, the prevalence of MS with both definitions was higher among individuals with high CV risk in the LT4 treatment group (p<0.05). For the prediction of CV risk, the sensitivity and specificity of the AACE criteria were higher than those of the WHO criteria in the LT4 treatment group.

Conclusions

The prevalence of MS in euthyroid patients treated with LT4 was similar to that of patients without thyroid disease. When the LT4 treatment group was classified based on CV risk, MS was more common in those with a high CV risk.

The Association Between Circulating Trans Fatty Acids and Thyroid Function Measures in U.S. Adults

BACKGROUND

There has been controversial evidence regarding the effect of trans fatty acids (TFAs) on thyroid function in animal studies, and the epidemiological studies are lacking. We aimed to investigate the potential associations between circulating TFAs and thyroid function biomarkers in a U.S. adult population sample.

METHODS

We performed a cross-sectional survey with 626 adults aged ≥20 years who participated in the National Health and Nutrition Examination Survey (NHANES) 2009-2010. Multivariable linear regression models were constructed to elucidate the relationships between circulating concentrations of TFAs (palmitelaidic acid, vaccenic acid, elaidic acid, linoelaidic acid and the sum of the four TFAs) and a panel of thyroid function measures.

RESULTS

For 626 adults, positive associations were found between palmitelaidic acid, elaidic acid and total thyroxine (TT4), between palmitelaidic acid and total triiodothyronine (TT3), and between linolelaidic acid and thyroid stimulating hormone (TSH), while linolelaidic acid was negatively associated with free thyroxine (FT4) (all P<0.05). Besides, the four TFAs and the sum TFAs were positively associated with free triiodothyronine (FT3). Vaccenic acid, elaidic acid, linoelaidic acid and the sum TFAs were positively associated with FT3/FT4, while the four TFAs and the sum TFAs were negatively associated with FT4/TT4 (all P<0.05). In stratified analysis, the associations between thyroid function measures and the ratios remained significant in female. For men, linolelaidic acid was negatively associated with FT4 and elaidic acid and the sum TFAs were positively associated with FT3. Furthermore, the associations between TFAs and FT3/FT4 remained significant.

CONCLUSION

Our findings revealed that TFAs exposure was associated with serum biomarkers of thyroid function. More researches are needed to evaluate the long-term health outcomes of these findings.

FT3/FT4 ratio is correlated with all-cause mortality, cardiovascular mortality, and cardiovascular disease risk: NHANES 2007-2012

BACKGROUND

Thyroid hormones play a vital role in maintaining the homeostasis of the cardiovascular system. The FT3/FT4 ratio can be used to evaluate the rate of T4-to-T3 conversion, reflecting the peripheral sensitivity of thyroid hormones. There is no study to investigate its relationship with death and cardiovascular disease (CVD) in the general population.

METHODS

This retrospective cohort study involved 8,018 participants with measured thyroid function and no prior thyroid disease who participated in the National Health and Nutrition Examination Survey (NHANES) from 2007 to 2012. Mortality status was determined by routine follow-up using the National Death Index through December 31, 2015.

RESULTS

During a median of 87 months of follow-up, we observed 699 all-cause deaths, including 116 cardiovascular deaths. In multivariate adjusted models, higher free thyroxine (FT4) was linked to increased all-cause mortality (HR, 1.15 per SD; 95% CI, 1.09-1.22), cardiovascular mortality (HR, 1.18 per SD; 95% CI, 1.01-1.39), and CVD risk (HR, 1.17 per SD; 95% CI, 1.08-1.27). Higher free triiodothyronine (FT3) was linked to decreased all-cause mortality (HR 0.81 per SD; 95% CI, 0.70-0.93). Higher FT3/FT4 ratio was linked to decreased all-cause mortality (HR, 0.77 per SD; 95% CI, 0.69-0.85), cardiovascular mortality (HR, 0.79 per SD; 95% CI, 0.62-1.00), and CVD risk (HR, 0.82 per SD; 95% CI, 0.74-0.92). The FT3/FT4 ratio stratified findings were broadly consistent with the overall results.

CONCLUSIONS

FT3, FT4, and the FT3/FT4 ratio were all independent predictors of all-cause death. FT4 and the FT3/FT4 ratio, but not FT3, were independent predictors of cardiovascular mortality and CVD risk. Along with FT3 and FT4, we should pay equal attention to the FT3/FT4 ratio in the general population.

Association between Abdominal Fat Distribution and Free Triiodothyronine in a Euthyroid Population

BACKGROUND

Obesity is closely related to thyroid hormones; however, the relationship between abdominal fat distribution and thyroid hormones has rarely been explored.

OBJECTIVES

This study aimed to explore the relationship between abdominal fat distribution and free triiodothyronine (FT3) and FT3 to free thyroxine (FT4) ratio (FT3/FT4) in a euthyroid population.

METHODS

The present study enrolled 1,036 participants (age range 27-81 years; 445 men and 591 women). The visceral fat area (VFA) and the subcutaneous fat area (SFA) were determined by magnetic resonance imaging. FT3, FT4, and thyroid-stimulating hormone were measured by an electrochemical luminescence immunoassay.

RESULTS

In both men and women, SFA increased according to the increase of FT3 and FT3/FT4 tertiles (p for trend <0.05), while VFA did not significantly change. In the multivariate stepwise regression analysis, SFA was independently and positively related to FT3 in both men and women, the standardized β (95% CI) were 0.183 (0.094, 0.272) (p < 0.001) and 0.089 (0.007, 0.171) (p = 0.033), respectively. Moreover, SFA was independently and positively related to FT3/FT4 in men, the standardized β (95% CI) was 0.196 (0.101, 0.290) (p < 0.001). However, VFA was not related to either FT3 or FT3/FT4 in both genders.

CONCLUSIONS

Abdominal subcutaneous fat was independently related to increased FT3 in a euthyroid population.

CASE FINDING FOR HYPOTHYROIDISM SHOULD INCLUDE TYPE 2 DIABETES AND METABOLIC SYNDROME PATIENTS: A LATIN AMERICAN THYROID SOCIETY (LATS) POSITION STATEMENT

OBJECTIVE

Latin American Thyroid Society (LATS) Hypothyroidism Clinical Practice Guidelines recommend case finding of hypothyroid patients in multiple and different situations that agree with other Society guidelines. However, the detection of hypothyroidism in type 2 diabetes mellitus (T2DM) or metabolic syndrome (MetS) patients is not mentioned in particular. In the recent years, several basic and epidemiologic studies have appeared showing that a lower thyroid function and MetS/T2DM are associated. Hence, the aim of this review is to manifest the LATS position on the diagnosis of hypothyroidism in both MetS and T2DM patients.

METHODS

A search was made in PubMed using the following terms: "hypothyroidism" AND "diabetes" OR "metabolic syndrome." The most relevant studies describing the prevalence and complications due to hypothyroidism in both MetS and T2DM patients were selected.

RESULTS

The current document reviews new information from studies that have shown that the prevalence of hypothyroidism is higher in T2DM patients (odds ratio [OR], 3.45; 95% confidence interval [CI], 2.5 to 4.7) and that diabetic complications are more prevalent in subclinical hypothyroidism (ScH). The incidence of T2DM is 1.09-fold higher with each doubling of thyroid-stimulating hormone (TSH) mIU/L (95% CI, 1.06 to 1.12), and the incidence of prediabetes increases 15% (hazard ratio, 1.15; 95% CI, 1.04 to 1.26) in patients with TSH >5 mIU/L. Similarly, MetS is more prevalent in ScH compared to euthyroid individuals (OR, 1.31; 95% CI, 1.08 to 1.60).

CONCLUSION

Thyroid function is affected in MetS and T2DM, and hypothyroidism is more common in these patients. Diabetic complications are more frequent in ScH patients. Therefore, LATS now recommends aggressive case finding of hypothyroidism in both MetS and T2DM patients.

ABBREVIATIONS

CI = confidence interval; GLUT4 = glucose transporter 4; HOMA-IR = homeostatic model assessment for insulin resistance; HR = hazard ratio; LATS = Latin American Thyroid Society; MetS = metabolic syndrome; OR = odds ratio; ScH = subclinical hypothyroidism; T2DM = type 2 diabetes mellitus; T3 = triiodothyronine; T4 = thyroxine; TSH = thyroid-stimulating hormone.

Association between thyroid hormone levels, body composition and insulin resistance in euthyroid subjects with normal thyroid ultrasound: The Kangbuk Samsung Health Study

OBJECTIVE

Thyroid hormones play crucial roles in the control of energy homoeostasis and can influence body composition. In contrast, the changes in body composition might influence thyroid hormone levels. We evaluated associations between thyroid hormone levels, body composition and insulin resistance in euthyroid subjects with normal thyroid ultrasound (US) findings.

DESIGN AND PATIENTS

This retrospective cross-sectional study included 36 655 euthyroid subjects who joined the medical health check-up programme at our institution. Serum thyroid hormone levels were analysed in association with body fat percentage (BFP), skeletal muscle mass index (SMI) and homoeostatic model assessment of insulin resistance (HOMA-IR). Linear regression analyses were performed to evaluate relationships between thyroid hormone levels and anthropometric parameters.

RESULTS

Mean age was 36.4 years, and 49% of subjects were female. In multiple linear regression analysis, serum-free triiodothyronine (FT3) levels exhibited positive associations with waist circumference (WC) and HOMA-IR and a negative association with body weight, body mass index (BMI) and SMI among both men and women. The association between serum-free thyroxine (FT4) levels and anthropometric markers showed inconsistent results in men and women. Serum thyroid-stimulating hormone (TSH) levels showed a positive association with HOMA-IR in both men and women.

CONCLUSIONS

Lower SMI was significantly associated with higher serum FT3 levels, the active form of thyroid hormone, in both men and women. Higher insulin resistance was positively associated with serum FT3 levels and inversely associated with serum TSH levels in euthyroid subjects with normal thyroid US findings.

Association between serum vitamin B12 levels and metabolic syndrome in a euthyroid population

AIMS

To determine the association between serum levels of vitamin B12 and metabolic syndrome (MetS) in a population of euthyroid adults.

MATERIALS AND METHODS

We carried out an analytical cross-sectional study in euthyroid adults of both sexes, who attended the outpatient service of a private clinic in Lima-Peru during the 2012-2016 period. Participants were divided into tertiles (low, intermediate and high) according to their serum vitamin B12 values. MetS was defined when three or more metabolic criteria were met by the participants. We elaborated crude and adjusted Poisson regression models to evaluate the association between the serum vitamin B12 tertiles and the presence of MetS. The reported association measure was the prevalence ratio (PR) with their respective 95% confidence intervals (95%CI).

RESULTS

We analyzed 346 participants, the average age was 38.3 ± 10.8 (SD) years, 117 (33.8%) were males, the serum vitamin B12 median was 364.1 (IQR: 274.2-473.4) pmol/L and the prevalence of MetS was 30.1% (n = 104). In the crude Poisson regression model, we found an association between the serum vitamin B12 tertiles and the presence of MetS, with marginal significance. The association gained statistical significance in the adjusted model by potential confounders; and compared with the low serum vitamin B12 tertile, the prevalence of MetS was 36% lower (aPR = 0.64; 95%CI: 0.43-0.96) among the high tertile group.

CONCLUSION

Euthyroid participants with elevated levels of serum vitamin B12 showed a lower prevalence of MetS compared to those who had low levels of this marker.

High free triiodothyronine and free-triiodothyronine-to-free-thyroxine ratio levels are associated with metabolic syndrome in a euthyroid population

AIMS

To determine the association between free triiodothyronine (FT3), free thyroxine (FT4) and free-triiodothyronine-to-free-thyroxine ratio (FT3/FT4) levels and Metabolic Syndrome (MetS).

MATERIALS AND METHODS

We carried out an analytical cross-sectional study in euthyroid adults of both sexes, who attended the outpatient service of a private clinic in Lima-Peru during the 2014-2016 period. Participants were divided into tertiles (low, intermediate and high) according to their FT3, FT4, and FT3/FT4 ratio values. MetS was defined when three or more metabolic criteria were met by the participants. ROC curves were constructed, and Youden's Index were used to identify the optimal cut-points of each thyroid marker. We elaborated crude/adjusted Poisson regression models to evaluate the association between the thyroid markers and the presence of MetS. The reported association measure was the prevalence ratio (PR) with their respective 95% confidence intervals (95% CI).

RESULTS

We analyzed 245 participants, the average age was 38.5 ± 10.3 years, 29.8% were males, and the prevalence of MetS was 31%. In the adjusted Poisson regression models, the prevalence of MetS was higher among the high FT3 tertile compared to the low tertile (aPR = 2.01; 95% CI: 1.22-3.34). The prevalence of MetS was higher among the intermediate FT3/FT4 ratio tertile and the high FT3/FT4 ratio tertile compared to the low tertile, (aPR = 1.78; 95% CI: 1.02-3.10) and (aPR = 2.80; 95% CI: 1.67-4.72); respectively. The highest areas under the curve (AUC) were found for FT3 and FT3/FT4 ratio with areas of 0.654 (95% CI: 0.58-0.73) and 0.649 (95% CI: 0.57-0.72); respectively.

CONCLUSION

Elevated levels of FT3 and FT3/FT4 ratio were associated with MetS in a euthyroid population.

Thyroid function and metabolic syndrome in the population-based LifeLines cohort study

BACKGROUND

The metabolic syndrome (MetS) is a combination of unfavourable health factors which includes abdominal obesity, dyslipidaemia, elevated blood pressure and impaired fasting glucose. Earlier studies have reported a relationship between thyroid function and some MetS components or suggested that serum free thyroxine (FT4) or free triiodothyronine (FT3) levels within the normal range were independently associated with insulin resistance. We assessed how thyroid function relates to MetS prevalence in a large population-based study.

METHODS

Data of 26,719 people of western European descent, aged 18-80 years from the Dutch LifeLines Cohort study, all with normal thyroid stimulating hormone (TSH), FT4 and FT3 levels (electrochemiluminescent immunoassay, Roche Modular E170 Analyzer), were available. MetS was defined with the revised National Cholesterol Education Programs Adults Treatment Panel III (NCEP ATP III) criteria. We calculated prevalence of all MetS components according to TSH, FT4 and FT3 quartiles.

RESULTS

At similar TSH levels and age (mean 45 yrs), men had significantly higher levels of FT4, FT3, blood pressure (BP), heart rate, total and LDL-cholesterol, triglycerides (TG), and creatinine, but lower HDL-cholesterol compared to women (all p < 0.001). In total, 11.8% of women and 20.7% of men had MetS. In men, lower FT4 levels were associated with higher prevalence of MetS and all MetS components. In women, lower FT4 quartile was only associated with a higher prevalence of elevated TG, waist circumference, and MetS. However, when corrected for confounding factors like age, BMI, current smoking and alcohol consumption, a significant relationship was found between FT3 and three MetS components in men, and all five components in women. Moreover, the highest quartiles of FT3 and the FT3FT4 ratio predicted a 49% and 67% higher prevalence of MetS in men, and a 62 and 80% higher prevalence in women.

CONCLUSIONS

When corrected for possible confounding factors, higher plasma levels of FT3 are associated with several components of the MetS. Only in men, lower FT4 is related to MetS. In the highest FT3 and FT3FT4 quartiles, there is a 50-80% increased risk of having MetS compared to the lowest quartile. Further studies are needed to assess the possible causality of this relationship.