July 5, 2000 -- The more physically active girls are beginning at age 12, the better their chances of preventing osteoporosis and improving their bone health, according to a recent study published in the July issue of Pediatrics.
Puberty and adolescence are important times for bones, and studies show that between 45 and 60% of a grown woman's peak bone mass is reached during this time. Osteoporosis, bone loss that produces weakened, brittle bones, generally occurs later in life and increases a person's risk of fractures.
Along with this study by Tom Lloyd, PhD, and his colleagues, several other studies have suggested that osteoporosis in women could be prevented or delayed by increasing the peak bone mass in girls during their teen years with increased physical activity and diet. Researchers have specifically examined whether daily calcium intake can prevent osteoporosis.
This study included data taken from 81 white females enrolled in the Penn State Young Women's Health Study. These girls provided diet records from the ages of 12 to 18, as well as self-reported sports-exercise scores during this time.
The girls gained an average of 42% of their total body bone mineral content and 19% of their total body bone mineral density (BMD) between the ages of 12 and 18. The higher the girls' sports-exercise scores, the higher their hip BMD. No associations existed, however, between daily calcium intake and total body bone mineral gain or hip BMD at age 18.
As with many other diseases that occur late in life, prevention is the key in osteoporosis. "Medicine should be moving more toward prevention of disease, and ... a lot of prevention of disease will rely on changing behavior," says Michael L. Power, PhD.
According to Power, good habits and good bone health start early in life. "One of the problems of treating bone disease is that it does not show up for a long time," he tells WebMD. "You cannot change someone's behavior when she is 72 years old and has already broken her hip. You need to start earlier, when these women are young." Power is a research associate at The American College of Obstetricians and Gynecologists in Washington, D.C.
"Because the skeleton is 40% calcium by weight and diminishes with disuse, it is logical that calcium intake and physical activity are necessary to optimize bone gain during adolescence," write the study authors.
They also point out that the tendency of Americans to be "couch potatoes" does nothing to help anyone's bones. "Despite the established benefits of regular exercise, we are becoming an increasingly sedentary culture," they write. "The decline in our physical activity is illustrated by the fact that total caloric intake for teen-age women has decreased from [roughly] 2,300 kcal/day in 1932 to [roughly] 1,700-1,800 kcal/day today, while body weight has increased."
The recommended daily calcium intake is 1,200 mg/day, although few people -- young or old -- achieve this. These authors, however, didn't find any relationship between calcium intake and good bone health, and many experts say that it is just one piece of the puzzle of osteoporosis prevention. According to Robert P. Heaney, MD, world-renowned expert in the field of osteoporosis, preventing bone loss requires a multifaceted approach.
"We have as much bone as we use, just as we have as much muscle as we use," says Heaney, the John A. Creighton University Professor and professor of medicine in the department of internal medicine at Creighton University in Omaha, Neb. In the absence of doing physical work, our bones will not be very strong, and no amount of calcium will stop that. On the other side of the coin, if we do have enough stress or enough of a workload to make strong bones, but not enough calcium, that won't work either."
- Between 45 and 60% of a woman's peak bone mass is reached during puberty and adolescence, and a higher peak bone mass means a lower chance of developing osteoporosis.
- In a recent study of teen-age girls, those who participated in more physical activity had higher bone mineral densities in the hip.
- Experts say that osteoporosis can be prevented, but this requires healthy behaviors and diet from a young age.