Newer, low-dose birth control pills seem to carry less stroke risk than high-dose pills for young women, but should be prescribed with care, according to an Australian study published in today’s rapid access issue of Stroke: Journal of the American Heart Association. The oral contraceptive pill (OCP) was introduced in the 1960s and, nearly simultaneously, researchers raised the possibility that it might induce stroke, says lead author Sasitorn Siritho, M.D. She conducted the study while a visiting research fellow at the National Stroke Research Institute, Austin & Repatriation Medical Centre in West Heidelberg, Australia.
From American Heart Association:Low-dose ‘pill’ may have less stroke risk for young women
DALLAS, June 13 ? Newer, low-dose birth control pills seem to carry less stroke risk than high-dose pills for young women, but should be prescribed with care, according to an Australian study published in today’s rapid access issue of Stroke: Journal of the American Heart Association.
The oral contraceptive pill (OCP) was introduced in the 1960s and, nearly simultaneously, researchers raised the possibility that it might induce stroke, says lead author Sasitorn Siritho, M.D. She conducted the study while a visiting research fellow at the National Stroke Research Institute, Austin & Repatriation Medical Centre in West Heidelberg, Australia.
“However, most studies that suggested an association between OCP use and stroke were done on formulations that typically contained 80 or 100 micrograms (?g) of estrogen, much higher than the 30-35 ?g of estrogen in the pills commonly used today. Little research has focused only on the newer formulations and a good deal of controversy remains on this issue,” she explains.
Researchers at four major Melbourne, Australia hospitals matched 234 women (ages 15 to 55) who had a stroke between 1984 and 1996 to 234 controls recruited from the same streets as the stroke patients. Nurses conducted detailed personal interviews, obtained a list of previous and current medications used by the subjects and details on family medical history.
The researchers found that women who reported currently using OCP with less than 50 ?g of estrogen seemed to be at no greater risk of ischemic stroke, the kind of stroke in which a blood clot blocks an artery supplying the brain. In addition, there was no association between the number of years a woman had taken OCP and the risk of stroke.
Although the odds ratio of stroke was 1.76 for women who used the low-estrogen OCP, that number did not reach the level of statistical significance, says co-author Amanda G. Thrift, Ph.D., head of epidemiology at the Australian institute.
Women who reported having stroke-like symptoms that went away within 24 hours, a condition called transient ischemic attack (TIA), had eight times the odds of developing an ischemic stroke than those without TIA, she says.
Current smoking increased the stroke risk, particularly smoking more than 20 cigarettes a day ? which nearly quadrupled the risk. “Importantly, this risk was diminished among past smokers,” Thrift adds. “Women with high blood pressure or a family history of stroke had double the risk of stroke.”
Because smoking, high blood pressure, diabetes and a family history of stroke all increase the risk of stroke, physicians should be very cautious about prescribing oral contraceptives to women in those groups, she says.
“Our study finds that OCP use is not associated with a statistically greater risk of ischemic stroke in healthy women when compared to those who are not currently using OCP, and other well-controlled studies have had similar results,” Thrift says. “However, some previous studies have found that low-estrogen OCP seems to double the risk of stroke and high-estrogen formulations seem to quadruple that risk.”
Some potential biases may have influenced the results of the study, researchers note.
“There may be differential recall among subjects because controls may have forgotten to mention past OCP use, and women who have had a stroke may have more reason to ponder the possible ’cause’ of the stroke, and both groups might not remember which formulations they took in the past or for how long,” Siritho says. “About 27 percent of the controls and 31 percent of the stroke cases reported using higher doses of estrogen birth control pills in the past.
“In addition, more than 45 percent of the patients were ages 45 to 55, and of those only 7.24 percent were current OCP users,” she says. “Because so few people were current users of the OCP in this group, it is possible that we have underestimated the association between OCP and ischemic stroke.”
