THURSDAY, Jan. 15 (HealthDay News) -- Newer formulations of birth control pills don't seem to increase the risk of heart disease as much as older forms did, a new study says.

But more research on the newer generations of contraceptives is needed to delineate the specific effects. This is especially true because more women over age 35 are taking hormonal contraceptives, they're taking them for longer periods of time, and the U.S. population is increasingly obese, said the authors of the study, published in the Jan. 20 issue of the Journal of the American College of Cardiology.

"Newer formulations that have come out in the last decade do not appear to raise blood pressure to the same degree that older formulations did, so we're calling for long-term research of newer formulations because they may be very good -- so good that we could even use them as prevention rather than contraception. Or they could be bad or there could be some other thing that's happening with newer formulations," said study co-author Dr. C. Noel Bairey Merz, director of the Women's Heart Center at Cedars-Sinai Heart Institute in Los Angeles.

"Hormonal contraception for young premenopausal women remains safer than pregnancy, so it's safe and effective for contraception," Bairey Merz added.

Hormonal contraceptives -- birth control pills, patches and vaginal rings -- are among the most commonly prescribed contraceptives. They're used by 11.6 million American women, or 19 percent. The Pill was introduced in the 1960s and 80 percent of women have used hormonal contraceptives at some point in their lives, according to background information in the study.

Newer forms of the pill contain less estrogen and so are safer while still being effective, the study authors said.

When an arm of the landmark Women's Health Initiative study was stopped because of elevated risks of breast cancer, stroke and other cardiovascular problems among older women taking hormone replacement therapy, new attention was focused on hormone products in general.

Also, the cardiovascular-related death rate for women aged 35 to 44 has increased since 2000, while decreasing among other groups of women. The obesity epidemic, lack of physical activity, smoking and a rise in the use of oral contraceptives (from 4 percent to 17 percent) among this group of women coincided with the increased mortality rate, the study authors noted.

The new review article found that while newer oral contraceptives pose no increased risk of heart attack for women using them, there does appear to be an increased risk of blood clots. There was no data available on cardiovascular health for the newest generation of hormonal formulations, the study said.

Current guidelines from the American College of Obstetricians and Gynecologists recommend against prescribing birth control pills for women who smoke, are over 35, and those who are obese because the risk for blood clots is increased.

They also state that oral contraceptives with certain doses of estrogen are safer than pregnancy for women aged 35 through menopause.

Women who have high blood pressure or high cholesterol levels need to be monitored and have their conditions controlled if they take oral contraceptives, the study said.

"If patients are hypertensive but are well-controlled, they can use hormonal formulations. Diabetics can use hormonal formulations," Bairey Merz said. "There are several categories of women, including women who smoke, who should not use hormonal contraception and that remains true in this era as well."

Dr. Suzanne Steinbaum, director of women and heart disease at Lenox Hill Hospital in New York City, noted that the "world has changed and women are having babies later. Each individual needs to be evaluated for oral contraceptives, and we have never really thought about this [over 35] group. I'm happy this article was written."

More information

For more on contraception, visit the U.S. Food and Drug Administration's Office of Women's Health.