Migraine patients may face a significantly increased risk of asthma as well as blinding headaches, a study suggests.

Researchers at St George's Hospital Medical School, London, compared the prevalence of asthma in nearly 65,000 migraine patients with an equal number of patients without migraine.

There is definitely some link between the two conditions

Dr Andrew Dowson

They found that the migraine patients were 59% more likely to have asthma.

Writing in the British Journal of General Practice, Professor David Strachan and his colleagues stress that the size of the study made the findings significant.

They accept that the study does not prove a link between the two conditions, and that other unknown factors may play a role.

However, they say: "If the association is real, its elucidation may help the understanding of disease mechanisms shared by migraine and asthma."

Muscle theory

One theory is that both conditions are linked to problems with the smooth muscle that lines both the blood vessels and the airways.

Previous research has also suggested a link between the two conditions.

A study by the US Collaborative Perinatal Project found that asthma was more common in children of mothers with migraine than in those whose mothers were migraine-free.

More recently, analysis of a 1958 British babies born in 1958 found that those with migraine were more likely to have asthma.

Dr Andrew Dowson, medical advisor to the Migraine Action Association, told BBC News Online that propranolol - the drug most commonly used to treat migraine - was known to exacerbate the symptoms of asthma.

Therefore, he said it was possible that people taking the drug were more likely to report symptoms of asthma.

However, asthmatics taking a drug called montelukast to control their condition had also reported fewer headaches - suggesting a similar biological mechanism behind the two conditions.

Dr Dowson said: "There is definitely some link between the two conditions, but what is not clear at the moment is whether it is a real link, or just a coincidental finding."

Migraine has also been linked to irritable bowel syndrome, nosebleeds and travel sickness.

The research is published in the British Journal of General Practice.