FRIDAY, Jan. 15 (HealthDay News) -- Oral contraception may decrease bone density in young women, a new study suggests.
Those taking birth control pills for more than two years, and those on the low-dose estrogen pills appear to have the greatest risk of decreased bone density in the spine and whole body, according to the researchers.
"I think the evidence is still emerging on this association, but our findings suggest that low-dose oral contraceptives with long-term use have some impact on bone density," said study author Delia Scholes, a senior investigator at the Group Health Research Institute of Group Health Cooperative in Seattle.
The findings were published in the January issue of Contraception.
What isn't entirely clear from this study of women under 30, explained Scholes, is what the long-term impact might be. Researchers don't know if the lower bone density findings are easily reversible just by stopping the use of oral contraceptives. They also weren't able to study if the lower bone density in these young women would translate to a higher fracture risk later in life.
But, "if oral contraceptives are indeed causing the approximately 5 percent lower spine bone density for oral contraceptive users versus non-users that we observed in our study, and if that impact is not reversed with oral contraceptive discontinuation or with other factors that may occur across the life span, a 5 percent lower bone density after menopause is associated with approximately 50 percent more osteoporotic fractures," said Scholes.
Almost 12 million American women are currently using oral contraception, according to background information in the study. And, the use of oral contraception is highest in women under 30, reports the study. That's important because the 20s are generally a time of peak bone mass production.
However, little is known about the effects of oral contraception on bone density. Previous studies have had conflicting results, with some showing no effect or a benefit on bone density while others suggest that oral contraceptives may inhibit bone mass accrual.
The current study was comprised of 606 woman between the ages of 14 and 30. The researchers reviewed oral contraceptive use, the duration of use and the estrogen dose in the contraception, and compared this to bone mineral density tests. The bone density test measured bone density in the hip, spine and whole body.
When the researchers compared oral contraceptive users to non-users they found that women taking oral contraception had average bone mineral density levels that were 5.9 percent less for the spine and 2.3 percent lower for the whole body. There was a trend for lower bone density in the hip as well, though this trend didn't reach statistical significance.
The researchers also noted a trend toward lower bone density in women taking oral contraceptives containing lower doses of estrogen, with the lowest readings in women taking formulations containing less than 30 micrograms of estrogen.
The researchers found no effects in the 14- to 18-year-old age group. However, Schole said it's important to note that contraceptive use was less in this age group than for the women between 19 and 30.
Scholes said the researchers suspect that the hormones in birth control pills are likely affecting normal hormone levels -- perhaps lowering normally circulating estrogen levels -- which then affects bone production.
"The studies on oral contraception and bone density have been conflicting," said Dr. Beatrice Chen, director of the Center for Family Planning Research at Magee-Women's Hospital at the University of Pittsburgh Medical Center. "Although this study adds to that information, I don't think young women should be scared into stopping birth control. Talk with your doctor about your own risk factors, and the risks and benefits of using oral contraception."
Chen said that studies on longer-term birth control, such as Depo-Provera, have shown that when the contraception is stopped, bone levels quickly return to normal.
If you're concerned about your bone health, Chen said that there are steps you can take to help prevent bone loss, including: consuming adequate calcium and vitamin D, participating in weight-bearing exercise and quitting smoking.
Learn more about your bone health from the National Institute of Arthritis and Musculoskeletal and Skin Diseases.
SOURCES: Delia Scholes, Ph.D., senior investigator, Group Health Research Institute, Group Health Cooperative, Seattle; Beatrice A. Chen, M.D., M.P.H., director, Center for Family Planning Research, Magee-Women's Hospital, University of Pittsburgh Medical Center; January 2010, Contraception