Thyroid and obesity: an intriguing relationship

Obesity is one of the most important health risks of our time. Thyroid dysfunction is associated with changes in body weight and evidence suggests that slight variations in thyroid function, albeit within normal limits, contribute to the development of regional obesity and the tendency to gain weight . A positive correlation has been identified between serum leptin and serum TSH levels in obese individuals , which could reflect the positive association between TSH and BMI reported in overweight individuals . Interestingly, a moderate increase in total triiodothyronine (T3) or free triiodothyronine (FT3) levels has been reported in obese subjects , suggesting a high conversion of T4 to T3 in patients with central fat obesity due to increased deiodinase activity as a compensatory mechanism for fat accumulation to improve energy expenditure . On the contrary, weight loss induces a significant reduction in both TSH and FT3 , thereby increasing rT3 due to reduced deiodination. Obesity and thyroid dysfunction are common diseases, and consequently clinicians should be particularly alert to the possibility of thyroid dysfunction in obese patients