From: Jane E Brody, NY Times
Most people don’t start thinking about the health of their bones until midlife or later, by which time it can be too late to do very much to protect against serious bone loss and resulting fractures.
Researchers who study bone health say concern about the strength of one’s bones should start in childhood and continue through adolescence, when the body builds most of the bone that must sustain it for the remaining years of life.
Once peak bone mass has been reached, further gains are minimal, so childhood through adolescence is the best time to pay attention to bone development. By age 20, girls have gained between 90 and 96 percent of their peak bone mass. For boys, the peak occurs a few years later.
About 26 percent of total adult bone is accrued in two years around the time that bone mass increases the most — at age 12.5 in girls and 14.1 in boys. The amount of bone added during those two years is about the same as what is typically lost in the 30 years between ages 50 and 80.
Lifelong studies have not been done in people, but the best available evidence strongly indicates that increasing peak bone mass in childhood by just 10 percent could delay osteoporosis, especially in postmenopausal women, by about 13 years.
Although nothing can be done about the three factors with the greatest influence on bone mass — age, gender and genetics — two others under personal control can make the difference between suffering crippling fractures in midlife and escaping the effects of osteoporosis until after age 90. Those are physical activity and the bone-building nutrients, calcium and vitamin D.
While the focus here will be on the effects of exercise, it should be noted that calcium consumption by adolescent girls is often seriously inadequate, compromising their ability to build strong bones that will last a lifetime.