Sep. 16, 1998 DALLAS, Sept. 15 -- Women taking low-dose estrogen oral contraceptives may not face an increased heart attack risk, say scientists in a study in today's Circulation: Journal of the American Heart Association.
"When it comes to heart attacks, the study indicates that this type of oral contraceptive is basically safe for healthy women," says Stephen Sidney, M.D., assistant director for clinical research at the division of research, Kaiser Permanente Medical Care Program, Northern California, based in Oakland. The researchers also found no differences between women taking pills containing either of the two forms of the hormone progestin commonly used in current oral contraceptives.
There has been concern about the potential increased risk of cardiovascular disease associated with taking "the pill" since oral contraceptives were introduced in the 1960s, says Sidney.
"Although several, but not all, of the early studies showed evidence of increased risk of heart attack, most recent studies have not found the same results," notes Sidney.
Furthermore, says Sidney, contraceptive formulations have changed over the years, and newer pills contain different amounts of estrogen and progestin than earlier versions. So whether the current generation of oral contraceptives -- which have less than half the estrogen of the older preparations -- would have similar effects on the risk of heart attack has been unknown.
In 1991 the National Institute of Child Health and Human Development funded dual investigations at Kaiser Permanente and at the University of Washington at Seattle to determine the relationship between current oral contraceptives and risk of heart attack. The current analysis pooled the results of both research groups, studying 271 women between the ages of 18-44 who had heart attacks and 993 women of similar age who had not suffered a heart attack.
After the researchers adjusted for heart disease risk factors such as smoking, obesity and high blood levels of cholesterol -- thereby focusing only on the use of oral contraceptives -- women who took birth control pills were no more likely to be at risk for heart attack than women who had previously taken the pill or had never used oral contraceptives, says Sidney.
About 68 percent of the women who had heart attacks were smokers, while smokers made up only about 22 percent of those who did not have a heart attack. The mean body mass index -- a measure of a person's percent of body fat and an indication of obesity -- of the women who had heart attacks was above 30, compared to 25.5 in the women who did not have heart attacks. The National Center for Health Statistics defines overweight as a BMI of 25-29 and obesity is defined as a BMI of 30 or greater.
Researchers concluded that the women who had heart attacks were also more likely to be smokers or obese or have other risk factors for heart disease, and that it was these risk factors, not the pill, that were responsible for their risk of heart attack.
Sidney's co-authors include: David S. Siscovick, M.D.; Diana B. Petitti, M.D.; Stephen M. Schwartz, Ph.D.; Charles P. Quesenberry, Ph.D.; Bruce M. Psaty, M.D., Ph.D.; Trivellore E. Raghunathan, Ph.D.; Joseph Keleghan, M.D.; and Thomas D. Koepsell, M.D.
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