EXERCISE, SMOKING, AND CALCIUM INTAKE DURING ADOLESCENCE AND EARLY ADULTHOOD AS DETERMINANTS OF PEAK BONE MASS

Objective-To evaluate the contribution to peak bone mass of exercise, smoking, and calcium intake in adolescents and young adults. Design-Prospective cohort study with end point measurement (bane mineral density) after 11 years' follow up for lifestyle. Setting-Five university hospital clinics. Subjects-264 (153 females, 111 males) subjects aged 9 to 18 years at the beginning of the follow up and 20 to 29 years at the time of measurement of bone mineral density. Main outcome measure-Bone mineral density of lumbar spine and femoral neck by dual energy x ray absorptiometry; measures of physical activity and smoking and estimates of calcium intake repeated three times during follow up. Results-In the groups with the lowest and highest levels of exercise the femoral bone mineral densities (adjusted for age and weight) were 0.918 and 0.988 g/cm(2) for women (P = 0.015, analysis of covariance) and 0.943 and 1.042 g/cm(2) for men (P = 0.005), respectively; at the lumbar spine the respective values were 1.045 and 1.131 (P = 0.005) for men. In men the femoral bone mineral densities (adjusted for age, weight, and exercise) were 1.022 and 0.923 g/cm(2) for the groups with the lowest and highest values of smoking index (P = 0.054, analysis of covariance). In women the adjusted femoral. bone mineral density increased by 4.7% together with increasing calcium intake (P = 0.089, analysis of covariance). In multiple regression analysis on bone mineral density of the femoral neck, weight, exercise, age, and smoking were independent predictors for men; with weight, exercise, and age for women. These predictors together explained 38% of the variance in bone mineral density in women and 46% in men. At the lumbar spine, weight, smoking, and exercise were predictors for men; and only weight for women. Conclusions-Regular exercise and not smoking is important in achieving maximal peak bone mass in adolescents and young adults.