People who suffer from migraines may be at a higher risk of having a stroke, a new review suggests.

Canadian and American researchers reviewed 14 previously published studies on a possible link between headaches and ischemic strokes.

Ischemic stroke is caused by a blood clot that blocks a blood vessel or artery in the brain.

Neurologist find the risk of stroke for migraine sufferers is higher than for non-sufferers

A migraine is a severe throbbing headache that can cause vomiting, nausea and a sensitivity to light, sound and smells. No one knows what causes migraines.

Ali Samii, a neurologist at the University of Washington, Mayhar Etminan, a clinical epidemiologist at the McGill University Health Centre in Montreal and their colleagues found the risk of stroke for migraine sufferers was 2.16 times that for non-sufferers.

In the general population, the risk of stroke is two in every 100,000. For people with migraines, the risk is still low at four per 100,000.

Dr. Michel Aubé

About 3.5 million Canadians are believed to suffer from migraines, which is the most common form of headache in young adults, the researchers said in Monday's issue of BMJ Online First.

Women who have migraines and take oral contraceptives were up to eight times more likely to have a stroke than those not taking the pill, but the researchers caution the figure is based on three studies.

The pill and smoking compound the danger of stroke for migraine sufferers, especially for women whose migraines come with "auras," periods of visual distortion, said Dr. Michel Aubé, a neurologist at Montreal Neurological Institute.

"I think it's important to try to avoid the risk factors if you have migraine, particularly migraine with auras and try to limit if it all possible the use of oral contraceptive medication," said Aubé, who has published books on migraines.

Migraine sufferers need not be alarmed at their vulnerability to stroke, which remains low, added Aubé.

The study's authors speculate an increased risk of stroke is related to reduced blood flow in the brain that accompanies a migraine.

More research is needed to investigate the risk factors and to explore the mechanism of the potential association, the researchers said.