A US study now links lightning to the onset of the severe headaches that plague millions, with 28 per cent of people more likely to experience a migraine on days when lightning struck within 40 km of their home.

The researchers’ work appeared in the journal Cephalalgia, and is based on headache logs and weather data for the two US states of Ohio and Missouri.

"We're very surprised and very happy with the results in that this is the first study to link lightning to migraines," said senior author Vincent Martin, from the University of Cincinnati College of Medicine in Ohio.

Migraines are severe headaches - sometimes accompanied by light sensitivity, visual hallucinations or nausea - that can disable a person for hours or even days at a time. The majority of migraine sufferers are women.

Martin told Reuters Health that a migraine may result from certain triggers, such as stress, lack of sleep and dehydration. Previous research has also found links between the onset of migraines and high barometric pressure, high temperatures and high humidity.

But most of the past studies on weather and migraines relied on an individual's observations and did not always account for other, possibly unseen, local weather conditions, the researchers wrote.

For the new study, they used information collected from three sensors that track lightning near Cincinnati, Ohio, and five sensors near St Louis, Missouri. Those sensors allowed the researchers to know when and where lightning struck, and the intensity of each strike.

They also used the headache diaries from two previous studies of 90 migraine sufferers in those areas who were between 18 and 65 years of age. In those diaries, the participants recorded their headaches for three to six months.

After comparing the weather data with the headache journals, the researchers found that a lightning strike within 40 kilometers (25 miles) of a person's house was linked to a 31 per cent increased risk of any kind of headache, and a 28 per cent increased risk of the more severe migraine headache.

Martin said that could mean an extra one to three migraines per month for an individual, but that it depends on the person and the weather.

As for how lightning might affect migraines, Martin said it could be that the electromagnetic waves and ozone created by the lightning have something to do with it.

"The other theory is that when these thunderstorms roll in they can create more allergy spores in the environment," he said, which could create problems for some people.

The researchers cannot say for certain that lightning causes migraine, even though they used a computer model to account for other meteorological changes that occur during a thunderstorm.

In an accompanying editorial, Hayrunnisa Bolay of Gazi University in Ankara, Turkey, warned that the study had limitations, including its failure to account for the participants' own individual risk factors.

"In brief, one can only conclude that weather conditions associated with lightning have the potential to induce headache in migraine patients," she wrote. - Reuters