Adolescent ballet dancers are at risk for injury due to low bone density. To some extent this is due to the physically demanding nature of ballet as a discipline. But to what extent do nutritional factors play a role? To answer this question, Burckhardt et al. (2011) examined whether dietary habits related to bone density in a sample of adolescent female ballet dancers.
Participants were 127 pre-professional dancers (average age of 16.7 years) who agreed to keep a 3-day food diary several months before they participated in a dance competition.
Diet records were examined and four classes of foods were identified: non-dairy proteins, dairy products, fruits and vegetables, and starchy foods.
Measures of bone mineral content and density at the femoral neck (hip area) and lumbar spine (lower back) were among the outcome variables and these were measured with dual-energy X-ray absorptiometry (DXA).
Descriptive data for the entire group indicated that, compared to age-referenced norms,
- body mass was within normal limits for only 42.5% of the dancers
- lumbar spine density was below the 5th percentile
- femoral neck density was above the 50th percentile
Diet recall data indicated that, in comparison to intake recommendations made by the Swiss Society of Nutrition,
- consumption of starchy foods and fruits and vegetables were within normal limits
- consumption of dairy products was low (approximately 1/2 of the recommended intake)
- consumption of non-dairy proteins was high (approximately 2x the recommended intake)
After accounting for a variety of variables that might relate to bone density (e.g., age, height, onset of menarche, hours of dancing each week), two general dietary trends were evident:
- Dairy intake was positively related to bone density (i.e., bone density increased as dairy intake increased)
- Non-dairy protein intake was negatively related to bone density (i.e., bone density decreased as non-dairy protein intake increased)
Conclusion and Commentary
Young female ballet dancers are at risk for low body mass and bone density. This is in part explained by the tendency for dancers to eat less to meet the aesthetic demands of the discipline. When low-calorie diets are followed, dancers are at risk for consuming inadqeuate amounts of micronutrients (vitamins and minerals). Attention should be given to meal planning to ensure nutritional needs are met.
The data from this study suggest that bone density, particularly in the lumbar spine, tends to be low among young dancers, and this can be explained by a number of factors. Regarding nutrition, these data suggest that calcium intake should be a particular area of focus. Given that dietary calcium content and supplementation were not directly assessed in this study, however, it’s premature to conclude that calcium intake is responsible for these findings. Nevertheless, dairy intake was positively related to bone density, and non-dairy protein consumption was negatively related to bone density–it therefore seems reasonable to promote replacing some non-dairy protein foods with dairy products in the daily diet. For those who are unable to consume dairy products, calcium supplementation may be useful.
An interesting finding from this study is the difference in bone density at the two sites (lumbar spine and femoral neck). Lumbar spine density was quite low, but femoral neck density was above average. This desirable finding may be due to the fact that the hip is the primary site of weight-bearing activity in ballet training. In addition to nutritional intervention, it would be interesting to see if supplemental weight-bearing activity (e.g., resistance training) would serve to reduce the risk of low bone density throughout the body.
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Source: Burckhardt, P., Wynn, E., Krieg, M., Bagutti, C., & Faouzi, M. (2011). The effects of nutrition, puberty and dancing on bone density in adolescent ballet dancers. Journal of Dance Medicine and Science, 15, 51-60.
Note: Ethnic group differences (Caucasian compared to Asian dancers) were evident for most variables. Please refer to the original article for these data.