Migraines accompanied by a blurring of vision known as "aura" double the risk of stroke, according to a study released Wednesday.
That risk becomes even higher for woman, persons under 45, and smokers, said the study, published in the British Medical Journal.
Women who use contraceptives that contain oestrogen boost the odds of suffering a stroke even further.
Up to 20 percent of adults -- three-quarters of them women -- suffer migraine headaches often characterised by vomiting or extreme sensitivity to light and noise.
Up to a third of these patients experience a so-called aura before or during the headache, typically described as a strange light, unpleasant smell or confusing thoughts.
Earlier research has uncovered a correlation between migraines and strokes, but did not distinguish between different kinds of migraines, or investigate possible links to other types of cardiovascular disease.
Scientists led by Markus Schurks of Brigham and Women's Hospital in Boston sifted through nine studies in an effort to fill in some of these gaps.
They found that migraines with aura push up the risk of strokes caused by reduced blood flow two fold, but uncovered no association between migraines of any kind and heart attacks or death due to cardiovascular disease.
The researchers recommend that young women who have migraine with aura should stop smoking and use oestrogen-free birth control methods.
"Clinicians need to identify young women with migraine, particularly those who are seeking oestrogen-containing hormonal contraception," concurred Elizabeth Loder of Harvard Medical School in a commentary, also in the British Medical Journal.
The absolute risk of stroke for most patients with migraine remains low, Loder said, "so a doubling of risk is not cause for panic."
"At a population level, however, this risk deserves attention between the prevalence of migraine is so high," she added.
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AFP 271645 GMT 10 09
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