Peripubertal moderate exercise increases bone mass in boys but not in girls: A population-based intervention study

On the basis of cross-sectional studies in elite athletes and longitudinal studies. physical activity in growing children has been suggested to enhanc e bone mineral acquisition and prevent osteoporosis later in life. The leve l of exercise in most of these studies is not applicable in a population on a day-to-day basis. The aim of this study was to determine whether moderat e increased exercise within the school curriculum from age 12 to 16 years w ould have anabolic bone effects. In a population-based setting of 40 boys a nd 40 girls the school curriculum was enhanced to physical education 4 time s per week for 3-4 years. Controls were 82 boys and 66 girls who had had ph ysical education twice a week over a corresponding period. Both cases and c ontrols were measured at age 16 years. Bone mineral content (BMC), areal bo ne mineral density (aBMD), bone size (femoral neck width) and volumetric BM D (vBMD) were measured in total body, spine and femoral neck (FN) by dual-e nergy X-ray absorptiometry. Data are presented as mean +/- SD. BMC (8 +/- 1 5%, p = 0.04), aBMD (9 +/- 13%, p = 0.002) and vBMD (9 +/- 15%, P = 0.001) were all higher in FN in the male intervention group compared with controls . FN bone size was no higher in the intervention group than in the controls . In girls, no differences were found when comparing the intervention group with controls. The results remained after adjusting for confounding factor s such as weight, height, milk intake and activity after school, in summary , we report that increased bone mass can be achieved in a population-based cohort of boys (but not in girls) by moderate increased physical activity w ithin the school curriculum from age 12 to 16 years. We speculate that the same results can be seen in girls if intervention starts at an earlier age. We conclude that increasing the physical education content of the Swedish school curriculum may improve bone mass in at least peripubertal boys.