OBJECTIVE To identify whether
calcium,
vitamin D, and/or dairy intakes are prospectively associated with
stress fracture risk among female adolescents. DESIGN Prospective cohort study. SETTING Adolescent girls living throughout the United States. PARTICIPANTS A total of 6712 girls aged 9 to 15 years at baseline in the Growing Up Today Study, an ongoing prospective cohort study. MAIN EXPOSURES Dairy,
calcium, and
vitamin D intakes assessed by food frequency questionnaire every 12 to 24 months between 1996 and 2001. MAIN OUTCOME MEASURE Incident
stress fracture that occurred between 1997 and 2004 as reported by mothers of the participants in 2004. Cox proportional hazards models were used to examine associations. RESULTS During 7 years of follow-up, 3.9% of the girls developed a
stress fracture. Dairy and
calcium intakes were unrelated to risk of developing a
stress fracture. However,
vitamin D intake was inversely related to
stress fracture risk. The multivariable-adjusted hazard ratio of
stress fracture for the highest vs the lowest quintile of
vitamin D intake was 0.49 (95% CI, 0.24-1.01; Ptrend = .07). We conducted a stratified analysis to estimate the association between
vitamin D intake and
stress fracture risk among girls participating in at least 1 h/d of high-impact activity, among whom 90.0% of the
stress fractures occurred, and found that higher
vitamin D intake predicted significantly lower risk of
stress fracture (Ptrend = .04). CONCLUSIONS
Vitamin D intake is associated with lower
stress fracture risk among adolescent girls who engage in high levels of high-impact activity. Neither
calcium intake nor dairy intake was prospectively associated with
stress fracture risk.