Associations between Sensitivity to Thyroid Hormones and Visceral Adiposity in Euthyroid Adults

Objectives: The study aimed to explore the association between thyroid hormone (TH) sensitivity and obesity assessed by body mass index (BMI) and visceral adiposity index (VAI) in euthyroid adults.

Methods: This cross-sectional study used the thyroid feedback quantile-based index (TFQI), thyroid stimulating hormone index (TSHI), and thyrotrophic T4 resistance index (TT4RI) to indicate central TH sensitivity, and VAI to assess visceral obesity. Participants were categorized according to tertiles. We used logistic and linear regressions to explore the association stratified by sex.

Results: The study enrolled 5411 men and 5749 women with normal thyroid function. Men with the highest tertile of TT4RI had 1 kg/m2 higher BMI compared with men with the lowest tertile of TT4RI (P=0.001) after adjustment for age, hypertension, hyperlipidemia, diabetes, hyperuricemia, and renal function. There was no significant difference in BMI across tertiles of TFQI and TSHI in men, and TFQI, TSHI, and TT4RI in women after adjustment for other risk factors. TH sensitivity indices were positively related to VAI after adjustment for confounders in women but not in men. There were 1.21 (95%CI:1.02-1.44, P=0.03), 1.43 (95%CI: 1.20-1.70, P<0.001), and 1.47 (95%CI: 1.23 - 1.75, P<0.001) times higher odds of having high VAI among women in the highest TFQI, TSHI, and TT4RI tertiles respectively, compared to women in the lowest tertile.

Conclusions: Reduced central TH sensitivity was associated with increased visceral adiposity in women but not men. Our findings supplemented the evidence of the importance of TH sensitivity to metabolic disorders, especially among women.