Subclinical Hypothyroidism and Metabolic Syndrome: A Common Association by Chance or a Cardiovascular Risk Driver?

Relationship Between Serum Thyrotropin Levels and Metabolic Diseases in Older Adults

CONTEXT

Subclinical hypothyroidism is associated with metabolic diseases; however, it remains controversial in older individuals.

OBJECTIVE

This work aimed to investigate the relationship between thyrotropin (TSH) levels and metabolic diseases.

METHODS

In this cross-sectional study, sampling was conducted from nationally representative general communities from 31 provinces in mainland China. A total of6791 older (aged ≥65 years) and 55 303 young participants (aged 18-64 years) were selected after excluding individuals with overt hyperthyroidism or overt hypothyroidism. According to the kit, TSH reference range (0.27-4.2 mU/L) and the age-specific TSH range previously formulated (an upper limit of 8.86 mU/L for older adults and 6.57 mU/L for young adults), the older adults and young adults were separately divided into 4 groups based on their TSH levels. Main outcome measures included anthropometric assessments, serum concentrations of thyroid functions, and various metabolic parameters.

RESULTS

In contrast to young adults, there was no significant increase in the prevalence of any metabolic disorders assessed in the slightly elevated TSH group (TSH 4.21-8.86 mU/L) compared to the euthyroid group (TSH 0.27-4.2 mU/L) among older adults. After adjusting for interference factors, a TSH level higher than 8.86 mU/L was found to be an independent risk factor for low high-density lipoprotein cholesterol (OR, 1.84; 95% CI, 1.14-2.98) and dyslipidemia (OR, 1.49; 95% CI, 1.09-2.04) when compared to the euthyroid group in older adults.

CONCLUSION

Slightly elevated TSH levels are not associated with an increased risk of metabolic diseases in older adults. Therefore, we recommend raising the upper limit of the TSH range for individuals aged 65 years and older.

Subclinical Hypothyroidism Represents Visceral Adipose Indices, Especially in Women With Cardiovascular Risk

Context

From previous studies, decreased thermogenesis and metabolic rate in the patients with overt and subclinical hypothyroidism lead to an increase in visceral adipose tissue (VAT) incidence, and which was associated with cardiovascular diseases. In this paper, we want to explore the relationship between various forms of VAT [pericardial (PCF), and thoracic periaortic adipose tissue (TAT)] and obesity indices [body shape index (ABSI), and body roundness index (BRI), Chinese visceral adiposity index (CVAI)] with subclinical hypothyroidism by gender.

Objective

This study aims to evaluate region-specific cardiovascular (CV) fat tissue (pericardial fat [PCF] and thoracic periaortic fat [TAT) and noninvasive visceral adipose indices (a body shape index [ABSI], body roundness index [BRI]), and Chinese visceral adiposity index [CVAI]) in patients with subclinical hypothyroidism (SCH) as compared to a control population and relative to variations in CV risk.

Methods

A total of 125 Taiwanese patients recently diagnosed with SCH (age: 52.9 ± 10.16 years, 41.6% female) and 1519 healthy volunteers (age: 49.54 ± 9.77 years, 29.0% female) were evaluated for this study. All participants underwent PCF and TAT assessment using a multidetector computed tomography scanner, ABSI, BRI, and CVAI evaluation using a mathematical formula. CV risk was classified by Framingham risk score (FRS).

Results

Multivariable logistic regression models showed that the independent association of TAT and BRI with SCH were stronger in women than men. The adjusted model associations (odds ratio [OR]; 95% CI) with SCH for TAT and BRI in women were 2.61 (95% CI, 1.03-6.97) and 2.04 (95% CI, 1.07-3.92). The incidences of TAT and BRI third tertile were also higher in women with SCH (SCH vs euthyroid, TAT third tertile, 9 [17.3%] vs 35 [7.9%], P = .04; BRI third tertile, 22 [42.3%] vs 111 [25.2%], P = .01). In addition to BRI and TAT, there were higher risks of CVAI in SCH with intermediate/high FRS, especially in women (OR; 95% CI, TAT: 4.01; 95% CI, 1.01-6.640; BRI: 6.91; 95% CI, 1.03-10.23; CVAI: 7.81 95% CI, 1.01-12.03).

Conclusion

Our findings show that patients with SCH have significantly greater TAT, BRI, and CVAI values than control groups, especially in women (with different FRS).

Burnout and metabolic syndrome among healthcare workers: Is subclinical hypothyroidism a mediator?

OBJECTIVES

Evidence suggests that subclinical hypothyroidism (SCH) is associated with burnout and metabolic syndrome (MetS). We examined the relationship between burnout and MetS among healthcare workers (HCWs) and investigated the potential mediation of SCH.

METHODS

This cross-sectional study included HCWs from a tertiary medical center; demographic data were obtained using a questionnaire. Burnout was evaluated according to the Chinese version of the Maslach Burnout Inventory-Health Services Survey (MBI-HSS). MetS and thyroid function data were obtained from a physical check-up. Logistic regression models were used to evaluate the adjusted odds ratio (aOR), and mediation analysis was employed to examine the mediation effect.

RESULTS

Among 945 non-doctor/nurse and 1868 doctor/nurse staff, MetS was 30% and 14%, respectively, and the prevalence of burnout was nearly 6.5%. The results showed that burnout induced higher aOR of MetS in the doctor/nurse group (1.27, 95% confidence interval [CI]: 1.05-3.62). Thyroid-stimulating hormone (TSH) showed a positive association factor of MetS in doctor/nurse group-adjusted burnout (aOR = 1.15, 95% CI: 1.01-4.19). A higher TSH level was associated with an increased odds of MetS in younger doctor/nurse staff with burnout syndrome (aOR = 1.74; 95% CI: 1.04-3.22). There was a borderline significant mediation effect of SCH in the association between burnout and MetS in doctor/nurse staff.

CONCLUSIONS

The results showed that higher TSH levels were positively associated with burnout and MetS in doctor/nurse professionals, especially in the young cohort. Burnout may rely on the borderline mediation effect of SCH, which is likely to affect MetS.

Sex differences in subclinical hypothyroidism and associations with metabolic risk factors: a health examination-based study in mainland China

BACKGROUND

The association between subclinical hypothyroidism (SCH) and metabolic risk factors in the general health examination-based population has been widely explored. However, the results have been inconclusive. Additionally, the sex differences in the prevalence of SCH and the association of SCH with metabolic risk factors remain unknown.

METHODS

We conducted this cross-sectional study using data from health examination-based participants between June 2016 and April 2018 in our health examination centre. Sex differences SCH and the association of SCH with metabolic risk factors were explored.

RESULTS

The total prevalence of SCH was 3.40% among the 5319 included participants, and 4.90% among the 2306 female participants, which was much higher than the prevalence of 2.26% among the 3013 male participants (p < 0.05). In males, the difference between participants younger than 60 and aged 60 or older was not significant (p = 0.104); while in females, the difference between participants younger than 40 and participants aged 40 or older was statistically significant (p = 0.023). Multivariate logistic regression analysis demonstrated that age (OR = 0.568, p = 0.004), body-mass index (BMI) (OR = 5.029, p < 0.001) and systolic/diastolic blood pressure (SBP/DBP) (OR = 5.243, p < 0.001) were independent predictors of SCH in females, but no metabolic risk factor was significantly associated with SCH in males. Further analysis revealed that the prevalence was much higher in participants with one or two metabolic risk factors than in those with no above metabolic risk factors regardless of age (p < 0.01).

CONCLUSIONS

Our study demonstrates that high BMI and/or high blood pressure are associated with SCH in female participants, and the prevalence of SCH among women with one or two metabolic risk factors ranges from 7.69-14.81%, which indicates that in such a population, serum concentrations of TSH and FT4 may be routinely screened in mainland China. Certainly, prospective, large-scale studies with long follow-up period are still necessary to further verify our results.