Changes in bone mineral content in male athletes. Mechanisms of action and intervention effects

Abstract

Objectives: To determine changes in bone mineral content (BMC) in male athletes, to examine the mechanisms of changes, and to evaluate the effects of intervention.

Design: Dual-energy x-ray absorptiometry (DEXA) tests were administered over a 2-year period, and calcium loss during training was determined by analysis of sweat and urine. Calcium supplementation was administered during year 2. SETTING--A midsouth university.

Participants: Eleven members of a college Division I-A basketball team.

Intervention: Based on observed calcium loss, athletes received differential levels of calcium supplementation. Intervention commenced the week prior to the fall training season and continued through postseason play. MAIN OUTCOME MEASURE--Changes in BMC.

Results: Total body BMC decreased 3.8% from preseason to midseason of year 1 (mean decrease, 133.4 g, P = .02), increased nonsignificantly by 1.1% (mean increase, 35.3 g, P = .22) during the offseason, but decreased an additional 3.3% during summer months when practices resumed (mean decrease, 113.1 g, P = .01). Dermal calcium loss averaged 247 mg [corrected] per training session. From preseason to late summer, there was an overall decrease of 6.1% in total BMC and a 10.5% decrease in BMC of the legs. Calcium supplementation was associated with significant increases in BMC and lean body mass.

Conclusions: Bone loss is calcium related and exercise is positively related to BMC provided that calcium intake is sufficient to offset dermal loss.