March 15, 2000 (Los Angeles) -- Researchers in Australia have found that women who take birth-control pills have a modest increase in bone density in their spines, especially during the first five years of pill use. "This is an interesting side effect of oral contraceptives," researcher Julie Pasco, PhD, tells WebMD.
Pasco and colleagues at the University of Melbourne studied 710 women ranging in age from 20 to 69. Of those women, 579 had taken birth-control pills. The authors measured bone mineral density over the whole body and at individual sites, including the spine, thigh bone, and forearm. They evaluated the participants' reproductive histories and lifestyles, including diet, exercise, smoking history, and alcohol consumption, but did not separate the women according to the type of pill they took. Their study appears in the most recent issue of American Journal of Obstetrics and Gynecology.
Spinal bone density was 3.3% greater in women who had taken the pill, the study authors found. The increase was greatest in the first five years of pill use, with those women showing an average increase of 3.2% in spine density. After five years, spinal bone density continued to increase by 0.2% per year, an amount that the researchers said was small but statistically significant. There were no differences in bone mineral density in the other areas studied.
Pasco, who is coordinator of the Geelong Osteoporosis Study in Melbourne, is cautious in drawing conclusions. "The prime use of oral contraceptives is still to stop conception," she says. "We do not advocate oral contraceptives for the improvement of bone mineral density, but they do appear to have a protective effect on the skeleton."
Elliott N. Schwartz, MD, co-medical director of the Foundation for Osteoporosis Research and Education in Oakland, Calif., says it is difficult to draw firm conclusions from this study because the investigators did not distinguish among the different types of pills the women took. "What we can say is that women on all of the birth control pills averaged an increase in spinal bone density," says Schwartz, who reviewed the study for WebMD.
Nevertheless, he says, "osteoporosis is a big problem, and anything that can increase a woman's bone mineral density should be looked at. It is worthwhile to explore strategies to improve bone mass in women who are past their peak bone mass, that is, anyone who is over 30" or is in the early stages of menopause. For these women, he says, the first line of defense for bone health should be lifestyle factors, including weight-bearing exercise and adequate consumption of calcium and vitamin D. Women should also "control lifestyle risk factors we think are bad, such as smoking and drinking a lot of alcohol."