Association between thyroid hormones and body fat in euthyroid subjects.

OBJECTIVE

Thyroid hormones disorders are associated with changes of body composition. However, the relationship between thyroid hormones and body fat in a euthyroid population is unclear. The aim of this study was to explore the association between thyroid hormones and body fat in a euthyriod population.

SUBJECTS

A total of 865 euthyroid individuals were recruited in this study. Subjects with thyroid diseases or diabetes and who were taking medications that could influence thyroid hormones, weight or glucose metabolism were excluded.

MEASUREMENTS

FT3, FT4, lipid parameters, fasting insulin (FINS) and blood glucose were determined, and homeostasis model assessment for insulin resistance (HOMA-IR) was calculated. Anthropometric measurements were taken, and body fat parameters were assessed.

RESULTS

Serum FT3 was slightly higher in body mass index (BMI) ≥25 kg/m(2) group than that in BMI <25 kg/m(2) group (P < 0·05). However, the difference was too small to have clinical significance. FT4 levels were not significantly different between the two groups. Body weight, BMI, waist circumference, hip circumference, waist-to-hip ratio (WHR), percentage of body fat (PBF), waist-fat-to-hip-fat ratio, FINS and HOMA-IR increased linearly with the elevation of FT3 adjusted for age and gender. A multivariate linear regression analysis revealed that fat mass, PBF, HOMA-IR and FT4 contributed significantly to FT3 levels.

CONCLUSION

Grouped according to BMI, overweight and obese subjects have similar thyroid hormones compared to those with normal weight. Body composition parameters increase with the elevation of FT3, and FT3 is associated with body fat parameters in euthyroid subjects.