Body mass index and thyroid function in adolescent girls.

The present research was conduted to examine the relationship between thyroid function and body mass index. A cross-sectional study was carried out in Lar province and its' vicinity in south of Iran. By stepwise random sampling from all public girls' high schools, 227 high school participants (aged 12-21) were selected. Serum samples were collected and assayed for Triiodothyronine (T3), thyroxine (T4), thyroid stimulating hormone (TSH), reverse triiodothyronine (rT3), free thyroxine (FT4), free triiodothyronine (FT3). Weight and height were measured and body mass index (BMI) were calculated (weight (kg)/height2 (m)). Subgroup analysis was done according to body mass index. TSH, T4 and rT3 were correlated with BMI (r = 0.66, p = 0.001 and r = 0.12, p = 0.05 and r = 0.65, p = 0.001, respectively). Adolescent girls with BMI > or = 25 kg m(-2) showed higher serum TSH, T4 and rT 3 than subjects with BMI < 25 kg m(-2) (p = 0.001, p = 0.05 and p = 0.001, respectively). Present results showed that, although thyroid function was normal in the studied participants TSH and rT3 were positively correlated to BMI. TSH and rT3 could present a marker of altered energy balance in overweight and obese adolescent girls.