Relationship of thyroid hormones and metabolic parameters in euthyroid women

Objective: Thyroid hormones play a role in metabolic regulation, yet their associations with obesity and insulin resistance in euthyroid individuals remain unclear. This study aimed to evaluate the relationship between thyroid-stimulating hormone (TSH), fT3, fT4, and the fT3/fT4 ratio with metabolic parameters in euthyroid women. Methods: In this retrospective cross-sectional study, 236 euthyroid women aged 18–65 were recruited from a tertiary hospital in Istanbul between May and September 2023. Participants were categorized as individuals with normal weight, overweight, or obesity. Thyroid hormones and metabolic parameters (waist circumference, triglycerides, HDL-C, insulin resistance) were analyzed. Statistical analyses included correlation tests and ANCOVA for age adjustment. Results: No significant differences in thyroid hormone levels were found across BMI groups after adjusting for age. TSH was positively correlated with BMI and triglyceride levels. fT3 and the fT3/fT4 ratio were positively associated with insulin resistance and negatively associated with HDL-C. Conclusion: fT3 and the fT3/fT4 ratio may reflect metabolic alterations in euthyroid individuals. These findings highlight the potential relevance of thyroid hormone evaluation in assessing metabolic risk, especially among individuals with obesity or insulin resistance. Further multicenter studies are warranted.