BONE MASS GROWTH DURING NORMAL PUBERTAL DEVELOPMENT

Bone mineral density (BMD, gr/cm2) and content (BMC, gr) were determined at the levels of the lumbar vertebrae (L2-L4), femoral neck (FN) and midfemoral shaft (FS) using DEX absorptiometry at 1-yr interval in 198 healthy adolescents (98 females, 100 males) aged 9-19 yrs. BMD/ BMC values were related to age, height, weight, pubertal stage and to environmental variables such as calcium intake and the level of physical activity. In females, the gain in BMD/BMC was sustained from 11 to 14 yrs but fell dramatically after 16 yrs and/ or 2 yrs after menarche. In males, the BMD/ BMC gain was elevated from 13 to 17 yrs and then declined markedly, remaining significant between 17 and 20 yrs for L2-L4 BMD/BMC and FS BMD only. Large interindividual variations were observed between height increments and bone mass gain with a relationship evolving according to a loop pattern. Multiple regression analysis showed that weight was the strongest predictor of bone mass at each site. Nutrition and exercise improved the R2 of the overall model by only 6% at L2-L4 and 4.1% at FN. Their effect on FS was negligible (+0.7%). During the normal pubertal development of average subjects, the effects of environmental factors appear to be outweighed by the large gain of bone mass due to puberty itself. These effects should therefore be easier to demonstrate in prepubertal children: this point appears of relevance for future intervention programmes aiming at maximizing bone mass gain during growth.