The effect of body weight and weight loss on thyroid volume and function in obese women

OBJECTIVE Thyroid volume and thyroid function may vary in obese and nonobese women. It is not known whether weight loss could affect thyroid volume and function in obese subjects. PATIENTS AND METHODS The study population consisted of 98 premenopausal euthyroid obese [body mass index (BMI) = 30 kg/m(2)] women (mean age 40.5 +/- 11.4 years) and 31 nonobese (BMI < 25 kg/m(2)) women (mean age 38.6 +/- 12.9 years). Weight, height, BMI, waist circumference, body fat percentage and fat weight of all subjects were measured. Thyroid function and thyroid ultrasonography were performed at baseline and after 6 months of obesity treatment. Subgroup analysis was done according to weight loss. RESULTS Thyroid volume (P = 0.021) and TSH concentration (P = 0.047) were higher; free T3 (P < 0.001) and free T4 concentrations (P = 0.045) were lower in obese women; however, all were still in the normal range. There was a positive correlation between thyroid volume and body weight (r = 0.319, P = 0.002), BMI (r = 0.504, P < 0.001), body fat percentage (r = 0.375, P = 0.001), body fat weight (r = 0.309, P = 0.01) and waist circumference (r = 0.386, P = 0.004). There was a positive correlation between TSH concentration and body weight (r = 0.227, P = 0.042) and body fat weight (r = 0.268, P = 0.038). After 6 months of obesity treatment, thyroid volume (P = 0.008) and TSH concentration (P = 0.006) decreased only in obese women who lost > 10% body weight. There was a positive correlation between the changes of thyroid volume and the change of body weight (r = 0.341, P = 0.009) and the change of body fat weight (r = 0.406, P = 0.013). CONCLUSIONS Our study suggests that thyroid volume and function may vary in obese women in association with body weight and fat mass; > 10% weight loss may affect thyroid volume and function, which however, is clinically insignificant.