A sweeping new Danish study concludes that hormonal contraception increases the risk of heart attack and stroke, but the overall risk for individual women is very low.
"The amount of attention paid to these minuscule risks, and what are likely to be very small differences in vascular risk, detracts attention from more salient issues, like preventing unwanted pregnancy," argued Dr. Diana B. Petitti, a professor of biomedical informatics at Arizona State University. Petitti wrote an editorial accompanying the findings, which were published in the New England Journal of Medicine on Wednesday.
Using national data on more than 1 million Danish women collected over a 15-year period, researchers examined whether various birth control formulations increased the risk of thrombotic stroke and heart attack. Thrombotic stroke occurs when a blood clot forms inside one of the brain's arteries, stopping blood flow and killing brain cells. Most heart attacks occur when a blood clot blocks one of the coronary arteries.
The study found an increased risk of heart attack and stroke tied to various estrogen-progestin birth control pills. The risks were small overall and virtually non-existent with the progestin-only formulas. With the vaginal ring or the patch, the risks were slightly higher.
But experts who looked at the Danish findings were quick to caution that the risks for individual women remained very low.
"The risk might be as much as two times greater, but when you know that the rates [of arterial thrombosis] are 1 in 10,000, you're just bringing it up to 2 to 4 in 10,000," explained Dr. Kathy Hoeger, director of the University of Rochester's Strong Fertility Center.
"It's a significant finding, and we wouldn't want to minimize that," she continued. "But the risk is relatively small."
The research did not look at the risk of deep venous thrombosis, or blood clots that form in a person's vein.
Other studies have linked pills containing the synthetic hormone drospirenone with increased risk of venous thrombosis, prompting the Food and Drug Administration to recently revise labeling for Beyaz, Safyral, Yasmin and Yaz contraceptives to reflect the possible risks. Bayer AG has agreed to pay $142 million to resolve more than 600 cases alleging Yasmin and Yaz led to the formation of sometimes fatal clots, Bloomberg reports.
"The main issue here is a very large study of a very rare outcome, which is arterial clotting, which can be much more serious and more deadly," Hoeger said of the Danish research.
There are certain subgroups of women who should be particularly careful about weighing the risks of hormonal birth control or avoid it altogether. For example, Hoeger said women in their 40s should talk to their doctor about their increased risk for clots, which may occur because of the general aging of the vascular system. In her editorial, Petitti also cautioned that women with high blood pressure should avoid hormonal birth control.
But overall, women and their physicians should be reassured by the Danish study, she wrote, describing hormonal contraceptives as "not risk-free, but safe enough."
"I'm hoping it refocuses attention on the issues of effectiveness, cost and convenience," said Petitti, pointing to a study published last month that found women on the pill, patch or vaginal ring were 20 times more likely to get pregnant than those using long-acting reversible contraception. "These are the issues we should be addressing."