Birth control pills reduce the incidence of heart attacks and other forms of cardiovascular disease and lower the risk of certain types of cancer, including ovarian and endometrial, researchers said Wednesday.
A team from Wayne State University in Detroit used the massive data available on 162,000 women in the Women's Health Initiative -- the same federal study that showed that hormone replacement therapy was much riskier than previously believed -- to provide the most definitive word yet on the safety of the pill.
Previous smaller studies looking at the link between the pill and cardiovascular disease have come down on both sides of the issue, with some showing a risk and others showing a benefit. Overall, said Dr. Michael Diamond of Wayne State, the consensus had been that the hormones in the pill -- estrogen and progestin -- increased the risk of heart disease.
The new findings, he added, should be "very reassuring" for women taking the pill.
The team presented the results Wednesday at an American Society for Reproductive Medicine conference in Philadelphia.
An estimated 16 million American women are on the pill and many times that number have taken the drug since the Food and Drug Administration approved it in 1960.
Diamond, Dr. Rahi Victory and their colleagues used data from 67,000 women who had taken the pill at one time or another compared to those who had never taken the pill.
They found that the hormones reduced the risk of hypertension, heart attacks, strokes, aneurysms and high cholesterol levels by 8% to 10%, Diamond said. It reduced the need for surgical procedures, including angiograms and bypasses, by 20% to 50%.
The longer the women took the pill, he added, the greater the reduction in risk.
Smoking negated many of the beneficial effects of the pill, he said, but smokers who took it still had a lower risk than smokers who did not.
Overall, women who took the pill had a 7% lower risk of cancer. Those who took the hormones for four years or longer had a 42% lower risk of ovarian cancer and a 30% lower risk of uterine cancer, he said.
The researchers found no effect on the incidence of other cancers, including breast, colon and bladder. That is a positive finding, Diamond said, because some studies had suggested that the pill increased the risk of breast cancer.
The researchers are not sure how the pill confers its benefits on users. Some studies in animals suggest that estrogen may reduce inflammation in blood vessels, keeping them more flexible and lowering the risk of clots.