"These findings are reassuring for those concerned about future risk of fractures," said Delia Scholes, PhD, senior investigator at Group Health Cooperative's Center for Health Studies and the study's lead investigator. "This information can be useful in helping young women balance the need to avoid unintended pregnancies with the need to build strong bones."
Scholes' study, which appears in the February 2005 issue of Archives of Pediatric and Adolescent Medicine, is the first to show that teen-aged Depo-Provera users' bone loss appears to be reversed once young women stop taking the contraceptive. The findings come less than three months after a decision by the U.S. Food and Drug Administration to issue a black box warning on Depo-Provera. The warning states that the drug is associated with bone loss that "may not be completely reversible."
While Scholes and her colleagues found that Depo-Provera use in women aged 14 to 18 was associated with continuous bone density loss at the hip and spine, they also found that users experienced significant gains after they quit using the drug. This provides evidence "that the loss of bone mass is apparently reversed," Scholes concluded.
In 2002, Scholes reported similar results among women aged 18 to 39. However, the current study shows that teen women who discontinued using Depo-Provera appeared to regain their bone density faster than older women did.
Teens use Depo-Provera at higher rates than older women do. About 10 percent of American women aged 15 to 19 who are using birth control use Depo-Provera, compared to just 3 percent of women in the U.S. overall. Given once every three months, the method is effective, relatively low in cost, private, and easy-to-use, Scholes explained. It is also a popular choice among young women for whom other types of contraception have failed.
How the study was conducted
The researchers measured hip, spine, and whole-body bone densities in 170 healthy teen women, aged 14 to 18, who get their care at Group Health Cooperative. The bone densities of the 80 participants receiving Depo-Provera injections were compared to those of 90 similar women who were not using this method. Bone density measurements were taken at the start of the study, and at 6-month intervals over a span of 2 to 3 years. During that period, 61 of the Depo-Provera users stopped using the drug, allowing the scientists to see how their bone density changed once they discontinued.
What the researchers found
As with previous studies, the researchers found that, compared to non-users, Depo-Provera users had significant loss of bone density in the hip and spine.
- Those who used Depo-Provera experienced an average loss of bone density at the hip of 1.81 percent per year compared with a loss of 0.19 percent per year among non-users.
- At the spine, women who used Depo-Provera had a bone loss of 0.97 percent, while those not using the drug had an increase in bone density of 1.32 percent. These bone-loss rates are similar to that of women who are breastfeeding or going through menopause.
- Women who were new Depo-Provera users lost bone density more rapidly than did longer-term users.
Once the Depo-Provera users stopped getting the injections, however, they gained a significant amount of bone density compared to non-users for the same period. For example:
- The average amount of bone gained in a year for women who quit using Depo-Provera was 1.34 percent at the hip, compared to a slight loss of 0.19 for women who were not taking the drug.
- Density at the spine increased 2.86 percent for women who quit the drug compared to an increase of 1.32 percent for women who were not taking the drug.
It's not clear from studies to date whether other hormonal methods of birth control might affect bone density, Scholes said. She and her colleagues are currently conducting a study of the effect of oral contraceptive use and discontinuation on women's bone density.
Scholes noted that a recent U.S. Surgeon General's report on bone health and osteoporosis provides a number of steps that teens and young women can take to improve or maintain bone density. The 2004 report recommends:
- Eat foods high in calcium and vitamin D
- Participate in regular weight-bearing exercise
- Don't smoke
- Limit consumption of alcoholic beverages
Scholes' study was funded by a grant from the National Institute of Child Health and Human Development, National Institutes of Health. The co-authors are Group Health investigators Andrea Z. LaCroix, PhD, Laura E. Ichikawa, MS, and William E. Barlow, PhD, and the University of Washington School of Medicine's Susan M. Ott, MD.
About Group Health Cooperative and the Center for Health Studies
Group Health Cooperative's Center for Health Studies conducts research related to prevention, diagnosis, and treatment of major health problems. Funded primarily through government and private research grants, the Center is located in Seattle, Washington. Group Health is a consumer-governed, nonprofit health care system that coordinates care and coverage. Based in Seattle, Group Health and Group Health Options, Inc. serve more than 540,000 members in Washington and Idaho.
Journal
Archives of Pediatrics and Adolescent Medicine