FRIDAY, Oct. 22, 2004 (HealthDayNews) -- The new finding that birth control pills may actually help a woman's health is raising several questions, not to mention a few eyebrows.
How could the hormones in oral contraceptives be protective when hormone replacement therapy (HRT) proved dangerous enough to cause the shutdown of one arm of the giant Women's Health Initiative (WHI)? To make matters more confusing, the conflicting results both come from studying women entered in the same trial.
Putting the paradox to rest seems to lie largely in looking at when women are using these hormones: If taken before menopause and the onset of cardiovascular problems, they appear to protect, but if taken once menopause has begun and heart trouble has started to surface, those same hormones can harm, researchers say.
According to the most recent study, presented this week at a meeting of the American Society for Reproductive Medicine in Philadelphia, women on the pill had an 8 percent lower risk of cardiovascular disease and a 7 percent decreased risk of developing any form of cancer. The protective effect seemed to increase over time, with women who had taken birth controls for eight or more years having a 42 percent lower risk of ovarian cancer and a 30 percent lower risk of uterine cancer. There appeared to be no increased risk of breast cancer.
Previous studies on heart disease had found either an increased risk or no increased risk. "We believe we are among the first to show a reduction," said lead author Dr. Rahi Victory, a fellow in the reproductive endocrinology and infertility program at Wayne State University School of Medicine in Detroit. The decreased risks of ovarian and endometrial cancer had been shown before. The breast cancer issue has remained controversial.
The hormone replacement arm of the WHI, on the other hand, found an increased risk of heart attack, stroke, blood clots and breast cancer among postmenopausal women taking estrogen plus progestin. The latest findings do not change this.
Part of the explanation for the seeming paradox lies in the women studied. Even though both studies looked at data from the WHI, the same women did not overlap in both. The current study looked at all women entered into that trial, just under 162,000 women. The HRT trial which was cancelled two years ago was a randomized, forward-looking trial of 16,000 women.
And as with so many things in life, even more of the answer lies with timing.
"It was a bit surprising, but it really shouldn't be," Victory said. "There's good evidence to indicate that when you expose women to estrogen in the premenopausal years, it's likely protective. There is molecular and animal evidence to indicate that estrogen can have benefits if there is no existing cardiovascular disease."
In postmenopausal women, on the other hand, estrogen may aggravate existing heart disease. "Younger women tend not to have existing heart disease, which may allow the estrogens to have a beneficial effect, rather than a detrimental one," Victory explained.
Biology also plays a part. "There are still many misconceptions about the safety of birth control pills because they contain progesterone and estrogen, which women associate with bad news about HRT," added Dr. Steven R. Goldstein, a professor of obstetrics and gynecology at New York University School of Medicine. "However, it's totally different because in premenopausal women, birth control pills shut down the ovary function, so these hormones are instead of what the ovary manufactures, not on top of it."
The types of hormones given also played a role. "The oral contraceptives and HRT are completely different," Victory said. "They have different formulations, different dosages, and widely varying progestin compounds."
This study, however, was not a randomized controlled trial, so the findings do need to be kept in perspective. "We think oral contraceptives are a safe thing to take," Victory said. "Can you say definitively that they are beneficial? No."
The bottom line is that it's important not to confuse these findings with previous findings from the WHI.
"HRT has definitively been shown to have risks in women who start it after being menopausal," Victory said. "We support the findings of the WHI and agree with them entirely. Our study suggests that oral contraceptives are likely safe and may be beneficial, but we are not recommending women take oral contraceptives to prevent heart disease and cancer, because that requires a study that can demonstrate causation, such as a randomized controlled trial. Because of the large population required and the multiple decades of time required to conduct such a study, it is unlikely it will ever be done."
More information
For more on the Women's Health Initiative, visit the National Institutes of Health.
