Objective: To determine whether low bone density and other risk factors for osteoporosis are associated with stress fractures in athletes.

Design: Case-control study.

Setting: Institutional sports injury clinic with primary and secondary care.

Participants: Twenty-five athletes (nineteen women) with scintigraphically confirmed stress fractures matched for sex, age, weight, height, and exercise history with 25 control athletes with no history of bone injury.

Measurements and main results: Bone mineral density measured by dual-energy x-ray absorptiometry was significantly lower in athletes with fractures than in control athletes: In the spine, bone mineral density was 1.01 +/- 0.14 g/cm2 in athletes with fractures and 1.11 +/- 0.13 g/cm2 in control athletes (P = 0.02). In the femoral neck, it was 0.84 +/- 0.09 g/cm2 in athletes with fractures and 0.90 +/- 0.11 g/cm2 in control athletes (P = 0.005). It was also significantly lower in the Ward triangle (P = 0.01) and the greater trochanter (P = 0.01). Eight athletes with fractures and no control athletes had less than 90% of predicted age-related spine density (P = 0.01), and three athletes with fractures had bone mineral densities that were 2 SDs or more below this predicted level. More athletes with fractures than control athletes had current menstrual irregularity (amenorrhea or oligomenorrhea) (P less than 0.005). Fewer athletes with fractures were using oral contraceptives (P less than 0.05). Seven-day diet records indicated similar energy and nutrient intakes, except athletes with fractures had lower calcium intakes (697 +/- 242 mg/d compared with 832 +/- 309 mg/d; P = 0.02). Dairy product intake was lower in athletes with fractures since leaving high school (P less than 0.05). The incidence of a family history of osteoporosis was similar in both groups.

Conclusions: In athletes with similar training habits, those with stress fractures are more likely to have lower bone density, lower dietary calcium intake, current menstrual irregularity, and lower oral contraceptive use.