Serum vitamin D level may be associated with body weight and body composition in male adolescents; a longitudinal study.

The prevalence of both obesity and vitamin D deficiency has been dramatically increased worldwide. This study aimed to investigate the association between vitamin D serum level and anthropometric indices of overweight and obese male adolescents at baseline and after 18 weeks of a weight reduction intervention. This study was carried out on 90 male students aged 12 to 16 years who were randomly selected from two schools in Tehran, Iran. The participants were assigned to two groups with high and low vitamin D level based on their serum vitamin D levels at baseline. Five ml blood samples were collected at the baseline and after the 18 weeks of a weight reduction intervention. Height, weight, body mass index (BMI), body fat percent and body muscle percent were measured using a bio impedance analysis (BIA) scale. Vitamin D level in non-obese adolescents was significantly higher than the obese participants (44.01 vs 37.67 ng/dl, p < 0.04). However, there was no significant correlation between changes of vitamin D level and anthropometric measurements after 18 weeks. Adjusting the effect of age did not alter the association. Further adjustments for physical activity, dietary intake of vitamin D, and fat and muscle percentage had no effect on the results. The serum level of vitamin D was negatively associated with obesity, but not with short-term changes of anthropometric measurements in male adolescents.