Association between thyroid hormones and body fat in euthyroid subjects

Area of Science:

• Endocrinology
• Metabolic Health
• Body Composition Analysis

Background:

• Thyroid hormone disorders significantly alter body composition.
• The specific relationship between thyroid hormones and body fat in euthyroid individuals remains unclear.
• Understanding this link is crucial for metabolic health assessment.

Purpose of the Study:

• To investigate the association between thyroid hormones and body fat parameters in a euthyroid population.
• To explore correlations between FT3, FT4, and various body composition metrics.
• To identify factors contributing to FT3 levels in healthy individuals.

Main Methods:

• Recruited 865 euthyroid individuals, excluding those with thyroid disease, diabetes, or relevant medications.
• Measured serum FT3, FT4, lipid profiles, fasting insulin (FINS), and blood glucose.
• Assessed anthropometric measurements, body fat percentage (PBF), and calculated homeostasis model assessment for insulin resistance (HOMA-IR).

Main Results:

• Serum FT3 was slightly, though not clinically significantly, higher in individuals with BMI ≥25 kg/m² compared to those with BMI <25 kg/m².
• Linear increases in body weight, BMI, waist circumference, hip circumference, waist-to-hip ratio (WHR), PBF, FINS, and HOMA-IR were observed with rising FT3 levels.
• Multivariate regression identified fat mass, PBF, HOMA-IR, and FT4 as significant contributors to FT3 levels.

Conclusions:

• Overweight and obese euthyroid subjects exhibit similar thyroid hormone levels to normal-weight individuals.
• Body composition parameters, including body fat, increase with elevated FT3 levels.
• FT3 is significantly associated with body fat parameters in the euthyroid population.