Indices of adiposity and thyroid hormones in euthyroid postmenopausal women

Abstract

Objective: We aimed to evaluate the association between thyroid hormones and indices of obesity in a sample of euthyroid postmenopausal women. Design: Cross-sectional study. Methods: Serum levels of TSH, free triiodothyronine (FT 3 ), and free thyroxine (FT 4 ) as well as BMI and waist:hip ratio (WHR) were evaluated in 194 healthy euthyroid postmenopausal women. Ultrasonography was used to assess abdominal fat layers (subcutaneous fat (SF), preperitoneal fat (PF), and SF:PF ratio). Indices of adiposity were defined as high vs low depending on the median value of the assessed parameters. Results: After multivariate adjustment for traditional risk factors, lower FT 4 levels and a higher FT 3 :FT 4 ratio predicted higher SF mass (FT 4 , Exp(b)Z0.035, PZ0.020 and FT 3 :FT 4 , Exp(b)Z2.374, PZ0.018), whereas higher FT 3 predicted higher PF mass (Exp(b)Z2.815, PZ0.032). Women with FT 3 :FT 4 above the highest quartile had a significantly higher SF mass as compared to women in the lowest quartile (1.81G0.62 cm vs 1.54G0.46 cm, PZ0.027). BMI had a positive independent association with TSH (Exp(b)Z1.829, PZ0.018). Finally, FT 3 was significantly associated with SF mass among women with higher BMI (FT 3 , bZ0.259, PZ0.040) and women with higher WHR (bZ0.309, PZ0.020) but not among women with lower BMI or WHR values. Conclusion: Thyroid hormone levels, and in particular FT 3 , were independently associated with SF and PF in euthyroid postmenopausal women, and this association was mainly evident in women with higher BMIs. On the other hand, among traditional indices of adiposity, only TSH was positively associated with BMI. Larger prospective studies are needed to evaluate the significance of the present findings.

Reference values for TSH may be inadequate to define hypothyroidism in persons with morbid obesity: Di@bet.es study

“…The changes in the thyroid hormone profile associated with BMI that we have seen in our study are concordant with previous reports that have consistently shown a positive correlation between BMI and TSH and between BMI and FT3 levels , whereas a paradoxical negative relation between BMI and other markers of adiposity and FT4 and a positive correlation with FT3/FT4 ratios have been described. This profile strongly suggests a high conversion of T4 to T3 due to increased deiodinase activity as BMI increases, possibly mediated by TSH.…”

“…In this context, previous studies have consistently reported a positive correlation between obesity and plasma thyroid‐stimulating hormone (TSH) levels . Along with higher TSH concentrations, persons with obesity have higher levels of free triiodothyronine (FT3) . Furthermore, longitudinal studies have shown a decrease in TSH and FT3 levels after substantial weight loss with diet or bariatric surgery.…”

Thyroid Function in Human Obesity: Underlying Mechanisms

“…In this respect, endocrine disorders stand out, and changes are observed in plasma levels, secretion patterns, and clearance of various hormones in obese individuals [5,6]. Regarding thyroid function, research has revealed the existence of a positive correlation between adiposity parameters and serum thyrotropin (TSH) and triiodothyronine (T3) in euthyroid individuals, suggesting a possible influence of obesity on the functioning of the hypothalamuspituitary-thyroid axis and the activity of deiodinases [7][8][9][10][11]. Changes in thyroid function, even within the normal range, may contribute to the worsening of ever, several mechanisms have been proposed including the adaptive process to increase energy expenditure, hyperleptinemia, changes in the activity of deiodinases, the presence of thyroid hormones resistance, chronic low-grade inflammation, and insulin resistance.…”

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

“…Magnetic resonance imaging (MRI) and computerized tomography are precise methods to measure abdominal fat and are internationally recognized [9]. Although several studies have explored the relationships between precise fat distribution parameters and FT3 [10][11][12][13], there exist large discrepancies among the results. In this study, we aimed to explore whether the MRI-measured visceral fat area (VFA) and subcutaneous fat area (SFA) are related to FT3 and FT3/FT4 in a euthyroid population.…”