PHILADELPHIA — The same huge federal study that led millions of women to abandon use of hormones after menopause now provides reassurance that another hormone concoction — the birth control pill — is safe.
In fact, women on the pill had surprisingly lower risks of heart disease and stroke and no increased risk of breast cancer, contrary to what many previous studies have found.
Doctors say the type of hormones and the stage of life when they're used may be what makes them helpful at one point and harmful at another.
"We're still learning more and more about the biology," said one of the researchers, Dr. Michael Diamond of Wayne State University in Detroit.
The new findings are from nearly 162,000 participants in the Women's Health Initiative, the largest women's health study ever done and one of the biggest on oral contraceptives. Results were presented Wednesday at an American Society for Reproductive Medicine conference.
About 16 million American women currently take birth control pills and hundreds of millions have used them since the first one came on the market in 1960. Most combine synthetic forms of estrogen and progestin in various doses.
Women taking these hormones after menopause were more likely to have heart disease and certain cancers — a finding that prompted part of this large study to be stopped in 2002.
Previous research on oral contraceptives suggested that they, too, raised the chances of heart disease. But the new study found the opposite — lower risk of heart attacks, strokes, high cholesterol, high blood pressure and other heart-related problems among the 67,000 women in the study who had ever taken the pill.
Overall, "there's an 8 percent risk reduction of ever having cardiovascular disease" among women who had ever taken birth control pills, said the lead researcher, Dr. Rahi Victory of Wayne State. "If you use oral contraceptives early on, you're probably going to be protected later in life."
Women on the pill also had a 7 percent lower risk of developing any form of cancer — a small benefit that increased with length of use, Victory said. For example, women who took birth control pills for four years or more had 42 percent lower risk of ovarian cancer and 30 percent lower chances of developing uterine cancer.
No effect was seen on the risk of some specific cancers — breast, colon or bladder. But that was good news because of the previous work suggesting pill use made breast cancer more likely.
Studies in animals suggest that estrogen may reduce inflammation in the bloodstream and help prevent deposits from forming and blocking vessels, Victory said. But that was seen in animals whose estrogen levels were relatively constant for a long time — not the situation of women whose estrogen declines before menopause.
"Those women went for a prolonged period of time without estrogen and then were re-exposed to estrogen" when they took so-called hormone replacement therapy after menopause, Victory said.
"By that time, they may already have atherosclerotic plaque in their arteries," Diamond added. "At that time, estrogen may aggravate the disease."
Dr. Robert Rebar, a gynecologist who is executive director of the reproductive medicine group, said the type of hormone may make a difference, too. Birth control pills contain four to six times the amount of estrogen as even the lowest formulations of hormone replacement therapy. But the most popular form of the latter uses estrogen derived from horse urine; birth control pills use a synthetic, manufactured form of it.
"That is totally different," he said. "We can't equate them."
The $625 million Women's Health Initiative study was done at 40 locations around the country and funded by the National Institutes of Health. Wyeth provided the hormone pills for the menopause portion of the study, but no oral contraceptive makers financed any part of that research.
On the Web: Women's Health Initiative: www.nhlbi.nih.gov/whi/
American Society for Reproductive Medicine: www.asrm.org/index.html