CHAPEL HILL - Oral contraceptives are known to increase the risk of heart problems for smokers, and new research at the University of North Carolina at Chapel Hill suggests that might be due in part to the specific type of hormones contained in "the pill."
Older "second-generation" oral contraceptives have a higher androgenic content because of the type of progesterone hormone used when compared to newer "third-generation" formulations.
For all women, older oral contraceptives produced higher blood pressures and more resistance to blood flow inside blood vessels during stressful situations, the UNC-CH School of Medicine study shows.
A report on the findings appears in the January issue of Obstetrics and Gynecology, a medical journal. Authors include psychology graduate student Patricia Straneva and Dr. Susan Girdler, assistant professor of psychiatry.
The UNC-CH study involved extensive testing of physiologic reactions of healthy women taking two different types of oral contraceptives, including 23 smokers and 23 nonsmokers, at rest and during mental and physical stress. Researchers induced stress by having volunteers perform rapid calculations, prepare and present short speeches and sit with a plastic bag of ice held to their foreheads for two minutes.
"Among smokers we found lower cardiac output, meaning that their hearts were pumping less blood, and greater vascular resistance, meaning that there was more tension in the blood vessels resisting blood flow," Straneva said. "This was not surprising considering the harmful effects of smoking on the heart."
Subjects who smoked and took older, more androgenic oral contraceptives showed the highest blood pressures and vascular resistance during stress, she said. All of the women, who were in their mid-20s, were healthy and had normal blood pressures when not under stress.
"Based on our findings, the type of progesterone should be an important consideration when determining which oral contraceptives to take, especially among women who continue to smoke," Straneva said. "For some women, the newer contraceptives may impart less risk, but that's a choice that ultimately needs to be made between a woman and her doctor."
The newer third-generation oral contraceptives might not be appropriate for all women, she said. One study suggested the medications might be linked with a higher risk of blood clot formation, while another more recent investigation indicated that might be true only for women genetically predisposed to clotting.
Some 22 million U.S. women continue to smoke, and many of them take oral contraceptives, Girdler said. Previous research has shown that smokers who take oral contraceptives face a higher risk of premature death than smokers who don't take oral contraceptives, and women who are on the pill but do not smoke.
However, those statistics were based on older formulations of the pill, some of which are no longer made, she said. Clearly, more research on newer formulations needs to be done.
The National Institutes of Health and the UNC-CH Women's Health Research Grants Committee supported the research. Other authors of the report were Dr. Alan Hinderliter, associate professor of medicine; Dr. Ellen Wells, assistant professor of obstetrics and gynecology; and research assistant Healther Lenahan.
While both smoking and oral contraceptives have been studied extensively, the new research is believed to be the first to examine cardiovascular responses to stress among smokers taking different formulations of the drugs. Its limitations included its relatively small size and that volunteers were not randomly assigned to the contraceptives they took.
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