Nutritional Factors That Influence Change in Bone Density and Stress Fracture Risk Among Young Female Cross‐Country Runners

OBJECTIVE: To identify nutrients, foods, and dietary patterns associated with stress fracture risk and changes in bone density among young female distance runners. DESIGN AND SETTING: Two-year, prospective cohort study. Observational data were collected in the course of a multicenter randomized trial of the effect of oral contraceptives on bone health. PARTICIPANTS: One hundred and twenty-five female competitive distance runners ages 18-26 years. ASSESSMENT OF RISK FACTORS: Dietary variables were assessed with a food frequency questionnaire. MAIN OUTCOME MEASUREMENTS: Bone mineral density and content (BMD/BMC) of the spine, hip, and total body were measured annually by dual x-ray absorptiometry (DEXA). Stress fractures were recorded on monthly calendars, and had to be confirmed by radiograph, bone scan, or magnetic resonance imaging. RESULTS: Seventeen participants had at least one stress fracture during follow-up. Higher intakes of calcium, skim milk, and dairy products were associated with lower rates of stress fracture. Each additional cup of skim milk consumed per day was associated with a 62% reduction in stress fracture incidence (P < .05); and a dietary pattern of high dairy and low fat intake was associated with a 68% reduction (P < .05). Higher intakes of skim milk, dairy foods, calcium, animal protein, and potassium were associated with significant (P < .05) gains in whole-body BMD and BMC. Higher intakes of calcium, vitamin D, skim milk, dairy foods, potassium, and a dietary pattern of high dairy and low fat were associated with significant gains in hip BMD. CONCLUSIONS: In young female runners, low-fat dairy products and the major nutrients in milk (calcium, vitamin D, and protein) were associated with greater bone gains and a lower stress fracture rate. Potassium intake was also associated with greater gains in hip and whole-body BMD.