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Depo-Provera Can Sap Bones of Young Women

Maker says damage from injected birth control is reversible

THURSDAY, Aug. 8, 2002 (HealthDayNews) -- Osteoporosis is thought of as a disease that attacks older women.

However, a new study shows about 2 percent of college-aged women already have osteoporosis, and as many as 15 percent more have significant bone density loss that's a precursor to the bone-weakening condition.

Who's at risk? Very thin white women, women who did not take part in exercise programs or sports in high school, and women on the contraceptive Depo-Provera, the study says.

"What I recommend is that anyone on Depo-Provera have their bone density tested if they can afford it to see where they're at and use that to make a decision about whether to keep taking it," says study author Lori Turner, an assistant professor of health science at University of Arkansas in Fayetteville.

Dr. Joel Krasnow, medical director for women's health at Pharmacia Corp., the maker of Depo-Provera, says previous research has shown a dip in bone density when taking Depo-Provera.

"It's real," he says. "There's no question of it."

However, Krasnow adds there are other important considerations when it comes to bone health.

Research has shown women on Depo-Provera lose about 2 percent of their bone density, but also that they regain the lost bone within one to two years of stopping the injected contraceptive.

Furthermore, the slight dip in bone density does not cause an increase in fractures in women on Depo-Provera. By menopause, "there is no difference in bone mineral density among those who took Depo-Provera compared to those who didn't," Krasnow says. That study included women who had been on Depo-Provera for 10 years or more.

"By the time you'd be at risk for fractures, which is during menopause, there is no difference in the bones," he says.

Krasnow adds the most serious threat to young women's bone health is dieting and failing to get enough calcium.

"What the study really shows is there are certain young women who have very low bone density, and a good part of the risk is due to a restrictive diet they are on -- probably to achieve what they consider an ideal body image," he says.

While Depo-Provera has been shown to decrease bone density by 2 percent, one landmark study showed calcium deficiency can cause a decrease in bone density of 18 percent, he says.

In the current University of Arkansas study, researchers using dual-energy X-ray scans measured the bone density in the hips and spines of 164 women aged 18 to 30.

They found women who had extremely low body weights were more likely than women of normal weight to have low bone density. The women who were very thin maintained their weight by dieting, Turner explains.

The low body weights meant they exerted less pressure on their bones. The pressure is needed to trigger bone growth, she says. A second factor in the low bone density was that many of the women had eliminated dairy products from their diets, hence losing their primary source of calcium.

Young women who participated in high school athletics had the highest bone densities.

Depo-Provera is a form of birth control that's injected and is effective for three months. The convenience, and the fact that's it's long-acting, is one of its main selling points. Depo-Provera is the hormone progestin, whereas birth control pills are a combination of estrogen and progestin. Estrogen is known to be instrumental in building bones.

"Clearly, if you have an unintended pregnancy, it's going to be a major disruption in your life," Krasnow says. "You have to put that into context of a slight decrease in bone density."

What To Do

To learn more about bone health, girls and teens can check out the Center's for Disease Control and Prevention National Bone Health Campaign. You can also visit the National Osteoporosis Foundation for more information on how to prevent the disease.

SOURCES: Lori Turner, Ph.D., R.D., assistant professor, health science, University of Arkansas, Fayetteville, Ark.; Joel Krasnow, M.D., medical director, women's health, Pharmacia Corp., Peapack, N.J.
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