Association Between Serum Thyroid-Stimulating Hormone Levels and Body Mass Index in Adults: A Cross-Sectional Study

Abstract

Background: Obesity and thyroid dysfunction are interrelated metabolic conditions, and variations in serum thyroid-stimulating hormone may reflect or contribute to altered energy balance and adiposity. Although previous studies have reported inconsistent findings, growing evidence suggests that higher body mass index may be associated with increased serum TSH even in individuals without overt thyroid disease. Objective: To determine the association between serum TSH levels and BMI among apparently healthy adults undergoing routine outpatient assessment. Methods: This cross-sectional study included 200 adults aged 18-60 years attending a tertiary care hospital for routine health examination between January and December 2025. Participants were categorized using Asian BMI cutoffs as underweight, normal weight, overweight, and obese. Serum TSH was measured by chemiluminescent immunoassay, and elevated TSH was defined as >4.0 mIU/L. Group differences in mean TSH were analyzed using one-way ANOVA with Tukey post hoc testing, while the association between BMI category and elevated TSH status was examined using chi-square testing and odds ratios with 95% confidence intervals. Results: Mean serum TSH increased progressively across BMI categories from 2.1 ± 0.8 mIU/L in underweight participants and 2.5 ± 0.9 mIU/L in normal-weight participants to 5.2 ± 1.7 mIU/L in overweight participants and 6.1 ± 2.0 mIU/L in obese participants (p < 0.001). Elevated TSH was observed in 0.0%, 4.0%, 47.5%, and 57.6% of participants in the respective BMI groups. Compared with normal-weight individuals, the odds of elevated TSH were substantially higher in overweight and obese participants. Conclusion: Higher BMI was significantly associated with increased serum TSH levels and a greater prevalence of elevated TSH, suggesting that thyroid function assessment may be clinically relevant in adults with excess body weight.