If they continued the calcium supplements for five years, said researcher Tom Lloyd, the girls could expect to increase their total bone mass by 5 percent. The ultimate result, he said, could be a 50 percent reduction in the risk of bone fractures caused by osteoporosis, a brittle bone condition linked to dwindling bone mass among the elderly, particularly post-menopausal women.
Mainly through the complications of hip fractures, the disease kills 50,000 Americans, most of them women, each year.
The new study, published in the Journal of the American Medical Association, shows that calcium supplements for adolescent girls would have a ''clear benefit" in later life, Lloyd said. It also suggests, he said, that the recommended daily allowance of 1,200 milligrams of calcium for
adolescents may be too low.
Last year, a similar study conducted at Indiana University also showed that taking calcium supplements in one's youth increases bone mass. In that study, researchers measured bone mass among twins, half of whom were given calcium supplements and half of whom were given placebos.
Many women begin worrying about taking additional calcium only in their later years, after bone loss has already begun. "But why close the door when the horse is out of the barn?" said Lloyd. "Why not do something in the way of prevention?"
However, two nutritionists on the American Academy of Pediatrics' Committee on Nutrition said yesterday that studies, including the one from Penn State, still have not proved that higher bone mass acquired during the teen years necessarily lasts throughout life.
Too many variables may intervene, including a woman's lifelong diet and her possible use of estrogen replacement therapy, which increases bone density after menopause, said committee chairman William Klish, a Houston pediatrician.
"The problem is that researchers can't be sure this had made any real impact until they follow these kids into their 40s to see if it has altered their bone densities," he said.
There was another complication with the new study: Researchers relied exclusively on tablets of calcium citrate malate, patented by the Procter & Gamble company and available to the public only in its Sunny Delight Plus Calcium and Double C Hawaiian Punch beverages. It cannot be assumed, Lloyd said, that there would be similar increases in bone mass among adolescents who take calcium supplements in other forms.