Lean body mass as a determinant of thyroid size

OBJECTIVE Males have a larger thyroid gland than females, and this has been related to the difference in body weight. In view of the different body composition of men and women, we hypothesized that lean body mass is a better determinant of thyroid volume than body weight. DESIGN A cross‐sectional study in an area not deficient in iodine. SUBJECTS 44 non‐obese healthy adults (group I, 21 men, 23 women with equal distribution of sexes in age groups between 21 and 70 years) and 20 adults with marked obesity (group II, 8 men, 12 women, BMI > 30 kg/m2) were studied. None used medication and all had normal thyroid function tests. MEASUREMENTS Thyroid volume was measured by ultrasonography, and lean body mass with a body impedance analyser. RESULTS The thyroid volume in men was larger than in women in both groups; it was also larger in the obese than in the non‐obese subjects. In the non‐obese subjects, thyroid volume was related both to body weight (r = 0.42, P