Effects of Calcium Intake and Physical Activity on the Bone Mineral Content andBone Mineral Density of the United States Naval Academy Midshipmen

摘要

Prevention of osteoporosis depends upon the identification of lifestyle factorsthat increase peak bone mass. We investigated the effects of calcium intake, weight bearing exercise (WBE), and strength training (ST) on total bone mineral content (TBMC) and bone mineral density (BMD) in 22 female and 13 male United States Naval Academy Midshipmen (MIDN). Each received 4 dual energy x-ray absorptiometry scans to measure TBMC and spine and hip BMD during the 2.8 year study period. Calcium intake was estimated at baseline and follow-up using a food frequency questionnaire. Frequency of WBE was determined at each visit using a questionnaire. The female's TBMC was predicted by calcium intake at baseline (p<.01) and increased during the study (p<.001) as did spine BMD. At follow-up calcium was a significant variable in a model predicting TBMC (p<.001), but was weaker than at baseline and not independent of body weight. In the male subjects, TBMC and spine BMD increased significantly (p<.005), (p<.05). Hip BMD did not increase in males or females. WBE was predictive of TBMC (p<.01), in female subjects weighing greater than 60 kg. This suggests that a threshold level of weight bearing (from body weight and exercise) is necessary to stimulate osteogenesis. We conclude that bone accretion occurs early in the third decade in MIDN and is highly influenced by body weight. Calcium intake and WBE in female MIDN may positively modify peak bone mass, although these effects were not independent of body weight.