Young women who have migraines with auras are twice as likely to have a stroke, researchers have confirmed.
Auras are sensory or visual disturbances that occur before or during a migraine headache.
Based on available evidence, the risk is greater if the woman is under 45, smokes and is on the contraceptive pill, say international experts.
But a migraine charity said most sufferers did not have auras and the absolute risk of a stroke was small.
Migraines affect between 10-20% of people and are four times as common in women compared to men.
Although the relative increased risk of stroke associated with migraine with aura is seemingly high, the actual risk is extremely low.
The researchers, writing in the British Medical Journal online, say they looked at nine of the most recent studies on the links between migraine and cardiovascular problems.
A previous large study in 2004 did find migraine sufferers had twice the risk of a stroke but the newer studies show that the risk is confined to people who suffer migraines with auras.
The investigators from the US, France and Germany did not find any link between migraines and heart attacks or death due to cardiovascular disease but there was a 30% increase in the risk of angina (heart pain).
Markus Schurks, of the Harvard Medical School and who led the research, said: “Clinicians may not agree but population studies show that up to a third of sufferers experience auras with their headaches.
“And when you consider that as many as 40% of young women suffer from migraines you can see that it really makes an impact on the health of the population.”
The authors recommend that young women who have migraine with aura should be strongly advised to stop smoking and methods of birth control other than oestrogen containing contraceptives should be considered.
They say recent animal studies have shown that high levels of oestrogen can produce auras in animals, so it could be the sex hormones affecting the vascular system, but more research is needed.
The British Heart Foundation recommended the women concerned reduce their risks as much possible – by switching to non-oestrogen based contraceptives, quitting smoking or contact their GP for further guidance.
Lee Tomkins, director of the charity Migraine Action, said: “I think this research will help women to understand that for the majority there is no additional risk, and for women with aura the best policy to help themselves is to have a migraine management plan in place that helps reduce the frequency of attacks, and try to minimize the aura part of the attack.”
Susan Haydon of The Migraine Trust stressed: “Although the relative increased risk of stroke associated with migraine with aura is seemingly high, the actual risk is extremely low.”
Dr Tony Rudd of The Stroke Association said: “Living a healthy lifestyle, taking regular exercise and having your blood pressure checked regularly are simple ways to reduce your risk of having a stroke.”