Washington: A study has found that birth control pills may reduce a woman`s bone density.
The study by Group Health Research Institute (GHRI) scientists showed that the impacts on bone were small, depended on the woman``s age and the pill``s hormone dose, and did not appear until about two years of use.
GHRI Senior Investigator Delia Scholes, PhD, who led the study, said that hormones are a key component of bone health, and hormonal contraceptives are a major source of external hormones for women.
A woman``s risk of fractures later in life is influenced by the bone mass she gains in her teens through her 20s, and this age group has the highest use of oral contraceptives.
"The teen years are when women most actively gain bone, so we thought it was important to look at that age group," Scholes said.
"We found that oral contraceptive use had a small negative impact on bone gain at these ages, but took time to appear, and depended on hormone dose," she stated.
The researchers measured hip, spine, and whole-body bone densities in 301 teen women aged 14-18, and in 305 young adult women aged 19-30, all Group Health Cooperative members.
After two years, teens who used 30-35 microgram pills showed about 1 percent less gain in bone density at both the spine and whole body sites than teens who did not use hormonal contraceptives.
For young adult women, users and non-users of oral contraceptives showed no differences in bone density at any site.
At 12-24 months after stopping, teens who took 30-35 microgram pills still showed smaller bone density gains at the spine than teens who did not use oral contraceptives.
At 12-24 months after stopping, young adult women who used either pill dose showed small bone density losses at the spine compared to small gains in women who did not take oral contraceptives.
Scholes says additional studies, including looking at bone changes for a longer time after pill use is discontinued, may tell us more about how oral contraceptive use is related to fracture risk.
For now, the results of Scholes`` study may help women make informed decisions.
"Bone health, especially for long-term users of the pill, may be one of many factors women consider in choosing a contraceptive method that``s right for them," she said.
The US Surgeon General recommends that women maintain bone density by eating foods high in calcium and vitamin D, getting weight-bearing exercise, not smoking, and limiting drinking alcohol.
The study has been published online July 13 in The Journal of Clinical Endocrinology and Metabolism.