Effect of Hypothyroidism on Body Mass Index

Abstract

Background: Thyroid hormones play a central role in regulating energy metabolism, thermogenesis, and body weight, with dysfunction of the hypothalamic–pituitary–thyroid axis strongly implicated in obesity. Hypothyroidism, characterized by elevated thyroid-stimulating hormone (TSH) and reduced thyroid hormone activity, is frequently associated with metabolic disturbances, but the strength and nature of its relationship with body mass index (BMI) remain debated. Objective: This study aimed to evaluate the association between serum TSH levels and BMI among hypothyroid and euthyroid individuals, thereby clarifying the contribution of thyroid dysfunction to obesity risk. Methods: A cross-sectional study was conducted on 50 participants aged 21–55 years, comprising 30 hypothyroid patients and 20 euthyroid controls from Sialkot, Pakistan. Anthropometric measurements were obtained to calculate BMI, and serum TSH was quantified using chemiluminescent microparticle immunoassay. Statistical analyses included group comparisons, odds ratios, and Pearson correlation with adjustment for demographic variables. Results: Hypothyroid patients exhibited significantly higher mean TSH levels compared with controls (7.62 ± 2.13 vs 2.11 ± 0.76 µIU/mL, p < 0.001, Cohen’s d = 3.11). Overweight and obesity prevalence was 60%, with significantly increased odds of obesity classes I and III. TSH correlated strongly and positively with BMI (r = 0.835, p < 0.001), explaining 70% of variance, persisting after adjustment for age and sex. Conclusion: Hypothyroidism is strongly associated with elevated BMI, with TSH serving as both a sensitive biomarker and predictor of obesity risk. Integrating thyroid screening into obesity management strategies may improve clinical outcomes and inform preventive interventions.