THURSDAY, April 17 (HealthDay News) -- Women who have weekly migraines are at an increased risk for stroke compared to those with few or no migraines, a new study finds.

On the other hand, those with less frequent migraines may have an increased risk of heart attack, the same team of researchers report.

The findings, to be presented Thursday at the American Academy of Neurology annual meeting in Chicago, point to different mechanisms linking migraines to distinct cardiovascular troubles, experts say.

And even though the average migraine sufferer's absolute risk of a heart attack or stroke is still low, the new study should be viewed in the context of other cardiac risk factors, said Dr. Richard Lipton, vice chairman of neurology at Montefiore Headache Center in New York City.

"Someone with migraine should be sure to manage their other risk factors including high blood pressure, diabetes, smoking, high cholesterol and body weight," said Lipton. He was not involved in the study, which was conducted by a team from Brigham & Women's Hospital and Harvard Medical School in Boston.

Previous research (much of it by the same group) has found an increased risk of vascular problems in both men and women who experience migraines, especially those who experience migraine with visual symptoms known as aura.

One recent study found that women who suffer from migraines with aura are at higher risk of stroke, especially if they smoke and take oral contraceptives.

What's been missing, however, is data on how the frequency of migraines might affect cardiovascular risk.

This study involved almost 28,000 female health professionals in the United States aged 45 and older, none of whom had cardiovascular disease when the trial started.

During about 12 years of follow-up, and compared to women with no migraines, women with less-than-monthly migraines turned out to be 54 percent more likely to develop cardiovascular disease. Those with weekly migraines were almost twice as likely to develop heart troubles.

Those with fewer-than-monthly migraines had a 45 percent increased risk of having an ischemic stroke (one resulting from constricted blood flow) and a 64 percent increased risk for heart attack, compared to women with no migraines, the Boston team found.

Women who suffered migraines at least weekly had a 49 percent increased risk for heart attack and almost triple the increased risk for stroke, they added.

According to Lipton, repeat migraine attacks may have a direct influence on the risk of stroke. "This is plausible because, during the aura, there are profound changes in the brain which diminish blood flow to the brain," he explained. "Stroke is usually caused by diminished blood flow to the brain."

If this were true, preventing migraines should decrease the risk of stroke, although this hypothesis has not yet been tested.

It's also possible that frequent migraines simply point to an increased risk for stroke, rather than actually causing it, Lipton said.

Either way, there's no reason to panic.

"Even if the relative risk of stroke triples in those with frequent migraine, the absolute risk for most people remains low," Lipton said. "If someone who would otherwise have a stroke risk of 20 per 100,000 has that risk triple due to frequent migraine -- to 60/100,000 -- they are [still] very unlikely to have a stroke."

More information

Find out more about migraines at The National Migraine Association.

SOURCES: Richard B. Lipton, M.D., professor and vice chairman, neurology, professor of epidemiology and director of population health, Montefiore Headache Center, New York City; April 17, 2008, presentation, American Academy of Neurology annual meeting, Chicago

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