Physical activity and bone mineral density in adolescents with vitamin D deficiency

Introduction: Studies have shown that physical activity (PA) is superior to many other environmental factors in determining bone mineral density (BMD), but none has examined the independent relationship between PA and vitamin D status. Purpose: The aim of this study was to assess the relationship among amount of PA, vitamin D (25(OH)D), and BMD. Methods: A total of 166 female ballet dancers and sedentary adolescents were divided by tertiles of serum levels of 25(OH)D (<11.3, 11.3-14.9, and >15 ng·mL^-1). Diet, PA, and menstruation were assessed by questionnaires; BMD was measured in three sites by dual-energy x-ray absorptiometry. Results: Across 25(OH)D tertiles, there were no differences in mean participant age, weight, height, PA, calcium and energy intake, BMD, or parathyroid hormone. PA was positively associated with BMD in participants with vitamin D deficiency. Multivariable regression analysis, controlling for age, body mass index, parathyroid hormone, and bone turnover markers, showed that total body, femoral neck, and lumbar spine BMD were all positively related to PA, with regression coefficients increasing as vitamin D levels dropped across tertiles. Conclusions: PA is positively related to BMD in vitamin D - deficient female adolescents and with increasing magnitude as serum vitamin D levels drop. These findings suggest that PA may counteract the detrimental effect of marked vitamin D deficiency on bone mass.