Stress fractures in female Army recruits: Implications of bone density, calcium intake, and exercise

Objective: To identify characteristics and factors associated with increased risk for stress fractures in military women. Design: Case-control study to retrospectively examine physical activity, prior calcium intake, and bone density as predictors of stress fractures. Setting: A military training installation which incorporates physical training for women. Subjects: Forty-nine female soldiers with confirmed stress fractures (cases) and 78 female soldiers with no orthopedic injuries (controls), aged 18 to 33 years. Measures: Retrospective self-reports of habitual exercise, sports participation, and food intake; current height, weight, and body mass index (BMI); demographic variables (age, ethnicity, menstrual patterns, smoking habits); and bone density on radiologically defined stress fractures. Results: Cases and controls were similar in height, weight, and BMI. Measurements of bone density (g/cm(2)) at the trochanter (cases, 0.77 +/- 0.09; controls, 0.77 +/- 0.08); femoral neck (cases, 0.94 +/- 0.10; controls, 0.94 +/- 0.09); Ward's triangle (cases, 0.91 +/- 0.11; controls, 0.93 +/- 0.11); lumbar spine (cases, 1.21 +/- 0.12; controls, 1.24 +/- 0.10); and radius shaft (cases, 0.67 +/- 0.09; controls, 0.68 +/- 0.05) were not different between groups. Calcium intake was not different between groups (cases, 1154 +/- 751 mg/day; controls, 944 +/- 513 mg/day) and did not correlate with bone density (r = 0.01 to -0.06 at four sites). Sports participation positively correlated with bone density in the hip (r = 0.49). Leisure activity energy expenditure (kcal/day) tended toward association with lower stress fracture risk as expenditure level increased (p = 0.06). Conclusion: Stress fracture in female Army recruits was not correlated with bone density or calcium intake during adolescence, although a weak relationship to prior physical activity was observed.