Vitamin D protects teen girls from stress fractures

Vitamin D, rather than dietary or supplemental calcium, effectively reduces incidence of stress fractures in adolescent girls who play high-impact sports.

Research suggests a possible association between high intake of calcium and increased likelihood of stress fractures.

Higher intake of vitamin D-not calcium or dairy products-lowers stress fracture rates among adolescent females who engage in high-impact exercise, according to new findings from the ongoing Growing Up Today Study.

Published online March 5 in the Archives of Pediatric and Adolescent Medicine, the prospective cohort study used questionnaires to determine the eating, supplement, and exercise habits of more than 6,700 girls aged 9 to 15 years from across the United States. The girls were daughters of women participating in the Nurses’ Health Study. For the purposes of the research, high-impact activities included basketball, running, soccer, tennis, cheerleading, and volleyball.

During 7 years of follow-up, 3.9% of the participants developed a stress fracture; 90% of those fractures occurred in girls participating in at least 1 hour of high-impact activity per day. The authors found that vitamin D intake was inversely related to stress fracture risk. Girls in the highest quintile of vitamin D intake had about half the risk of those in the lowest quintile (multivariable-adjusted hazard ratio of stress fracture for the highest versus the lower quintile of vitamin D intake was 0.49; 95% CI, 0.24-1.01; P_trend=.07).

No evidence was found to indicate that calcium or dairy intake was protective; one stratified analysis indicated that high calcium intake was associated with an increased risk of stress fracture, an “unexpected finding” warranting further investigation, according to the authors. In addition, they found no evidence that soda intake was detrimental.

The findings support the Institute of Medicine’s recent increase in the Recommended Dietary Allowance for vitamin D in adolescents from 400 to 600 IU per day. The average daily vitamin D intake of the girls in the study was 376 IU.

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