WEDNESDAY, June 24, 2009 (HealthDay News) -- The research team that found an increased risk of stroke in women who had a certain kind of migraine now reports a relationship between migraine frequency and heart attacks.
"Our earlier study showed an increased risk of ischemic strokes in women with a higher frequency of migraine headaches with aura," said Dr. Tobias Kurth, lead author of a report in the June 24 issue of Neurology. "Our new data confirms this. What we add is data in regard to coronary disease."
But the finding is "complex," varying with migraine frequency, said Kurth, an assistant professor of neurology at Harvard Medical School and a senior scientist at INSERM, the French national institute for medical research. "We see a U-shaped association -- an increased risk of myocardial infarction [heart attack] in the low-frequency migraine group and an increased risk for stroke in the high-frequency migraine group, those who have headaches at least weekly," he explained.
In both studies the association with stroke or heart attack is seen only in women who have migraines accompanied by an aura, a visual disturbance such as seeing flashing lights before the headache starts.
Women who had migraine with aura at least once a week were four times more likely to have a stroke as women who do not have migraine, the study found. Women who had migraine with aura less than once a month were more than twice as likely to have a heart attack and nearly twice as likely to have had coronary procedures such as bypass surgery. Migraines with aura once a month were not associated with increased risk of stroke or heart attack.
The findings come from an analysis of the Women's Health Study, which includes nearly 28,000 U.S. women health professionals who had no heart or brain blood-vessel problems at the start and were followed for 12 years. Of the 3,568 women with migraine at the start of the study, 75 percent had migraine less than once a month, 20 percent had migraine once a month and 5 percent had migraine at least once a week.
The study results should not make women with migraine headaches fearful, Kurth said. "Despite a very large study group, only a few participants who had migraine actually had a stroke," he said. "Only a very few people who had migraine with aura eventually have a stroke."
There is no clear explanation for the difference between risk of stroke and risk of heart attack in the migraine group, Kurth said. "The clinical application at the moment is unclear," he said. "It is unclear whether changing migraine frequency would affect cardiovascular events. At this point it is a research finding without much patient or clinical application."
Dr. Cheryl D. Bushnell, associate professor of neurology at Wake Forest University Health Sciences in North Carolina, said she agrees. "I don't think this is the kind of paper that can be presented to a patient and provide counseling," she said.
She anticipates updates on the relationships. "They have more events now than they did in the first report, and there could be some fluctuations that could occur as they continue to gather events," she said.
The data on the relationship with less-frequent migraines is not as solid as it might be, said Dr. Richard Lipton, director of the Montefiore Headache Center in New York City. "The confidence intervals are very broad for that group, but the results are unequivocal for the high-frequency group," Lipton said. "My inclination is that the figure for the once-a-month group is a blip, and the real finding is an overall risk associated with frequent migraines."
Lipton added, "All we have now is observational data on migraine. The sort of data I would love to see would be to give preventive medicine and see if it is associated with a reduction of stroke risk."
The researchers said other factors, including vascular risks, use of birth-control pills and smoking, appear to play a role in the connection between cardiovascular disease and migraines with auras. Further study is warranted, they said.
Learn all about migraine from the U.S. National Library of Medicine.