Vitamin D and muscle strength in female dancers and gymnasts

The discovery of the vitamin D receptor in skeletal muscle suggests a relationship between vitamin D status and muscular function. Although well investigated in the elderly, there are only a small number of cross-sectional studies investigating the relationship between vitamin D status and muscle strength and power in younger populations. Little is known about the implications of deficiency on athletic performance but athletes spending hours training and performing indoors are at risk and may not be achieving their greatest performance potential. Young female gymnasts and dancers have been shown to have low vitamin D status, and additionally are at risk of low iron status related to poor diet, in particular a low energy intake. The bone mineral density (BMD) of this group is also often compromised by poor dietary calcium and protein intake, negative energy balance and delayed menarche. For this study we will recruit 100 adolescent female ballet dancers and gymnasts. They will be randomly assigned to receive either a vitamin D supplement or a placebo for 12 months. Changes in muscle strength and power, and bone mineral density will be the primary outcome measures. Vitamin D and iron status, dietary assessment and body composition will also be measured.