Oct. 27 (HealthDay News) -- Women who get migraine headaches with aura should stop smoking and using birth control pills because they may increase their risk of stroke, researchers say.

For people who suffer migraine headaches with aura -- visual disturbances before or during the migraine -- the risk for ischemic stroke is doubled, they found. Being female, under 45, smoking and using oral contraceptives that contain estrogen added to the risk.

Ischemic stroke is caused by a blockage in a blood vessel. The connection between migraine and stroke was already suspected. What was unknown was the extent of risk and who is most at risk, the researchers said.

Migraine headaches affect up to 20 percent of the population. Women are up to four times more likely than men to get migraines, and as many as one third also experience an aura before or during a migraine.

"Migraine with aura is associated with a twofold increased risk for ischemic stroke compared to people without migraine, while migraine without aura does not appear to change the risk," said lead researcher Dr. Markus Schurks, from the division of preventive medicine at Brigham and Women's Hospital in Boston.

"But, considering the low absolute risk, there is no reason to panic, but modifiable risk factors such as smoking and oral contraceptive use should be considered," he said.

The report is published in the Oct. 27 online edition of the British Medical Journal.

For the study, Schurks and colleagues analyzed nine studies concerning the association between migraine, with and without aura, and cardiovascular disease.

"The risk appears to be highest among women with migraine with aura who smoke and use oral contraceptives," Schurks said.

In contrast, migraine alone does not appear to alter the risk for heart attack and death from cardiovascular disease, he added.

"In the scheme of things, aura is just one among many potential risk factors for stroke, so it is important to put this in context," said Dr. Elizabeth Loder, chief of the division of headache and pain at Brigham and Women's Hospital and author of an accompanying journal editorial.

"The risk of stroke for most people with migraine is low -- stroke is an uncommon event -- and so a doubling of that low baseline risk is not cause for alarm," she said. "Although it's not a reason for panic, having aura is a reason to pay extra attention to other stroke risk factors that can be modified. These include high blood pressure, high cholesterol, smoking and use of estrogen-containing contraceptives."

Other experts agreed.

Dr. Vincent Martin, an associate professor of medicine at the University of Cincinnati, said that "we have always known that the risk of stroke increased in patients with migraine, but this clarifies the situation in terms of which groups of migrainers are at more risk."

"If you are a female and you've got migraine with aura, you really need to be careful about managing your risk factors for stroke, because your risk for stroke is increased," he said. Smoking and birth control pills just aren't a good idea, he added.

SOURCES: Markus Schurks, M.D., division of preventive medicine, Brigham and Women's Hospital, Boston; Elizabeth Loder, M.D., M.P.H., chief, division of headache and pain, Brigham and Women's Hospital, and associate professor, neurology, Harvard Medical School, Boston; Vincent Martin, M.D., associate professor, medicine, University of Cincinnati, Ohio; Oct. 27, 2009, BMJ, online