Weather can trigger a migraine, US researchers have conclusively proved.
More than half of people with headache were affected by the weather, Dr Patricia Prince at Boston's Children's Hospital found.
Some were sensitive to temperatures and humidity, while others reacted to changes in air pressure, Dr Prince's team report in the journal Headache.
They said those prone to "weather" migraines could track forecasts to pre-empt and prevent an attack.
Other researchers have suggested weather could act as a trigger for migraine, much like caffeine and changes in sleep can set off an attack in those susceptible.
But studies have had mixed results.
Weather patterns
Over two years, Dr Prince, and colleagues from the New England Center for Headache in Stamford, studied 77 people attending their migraine clinic.
Each of the patients were asked to fill in a questionnaire asking how strongly, if at all, they believed their headaches were linked with the weather.
The researchers then compared the responses with daily weather reports from the regions where the patients lived at the time.
Overall, 48 (62%) of the patients believed the weather had been responsible for their migraines at some point.
When the researchers looked at the weather patterns in the days around the migraine attacks, they found only 39 (51%) of the patients were actually sensitive to the weather.
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Identifying trigger factors, such as weather, is important as it can lead to preventive strategies
"
Lead researcher Dr Patricia Prince
Among those who were affected by weather, the most common trigger was a combination of high or low temperatures and humidity.
Some were sensitive to high temperatures with high humidity and some were sensitive to low temperatures and low humidity.
Others were sensitive to major changes in the weather over a 1-2 day period and high or low air pressure or changes to more than one weather factor.
In most cases, the patient blamed a weather trigger that was not actually the one that had caused their migraine.
Whether the patient was old or young, male or female did not appear to matter.
Dr Prince said if patients were taught which factors triggered their migraine they would be better armed to prevent an attack.
"Identifying trigger factors, such as weather, is important as it can lead to preventive strategies such as trigger avoidance or taking acute care medications very early in the attack or even in advance," she said.
Dr Anne MacGregor, trustee and director of clinical research at the City of London Migraine Clinic and acting general secretary of the International Headache Society, said this was an important piece of research.
Credible
"They looked at changes in weather in several days even before the people had developed a headache which makes it much more credible than other studies that have just looked at the day of the headache and the weather on that day.
"It takes time for a migraine attack to build up and develop," she said.
She said many people with migraine linked their attacks to stormy, heavy weather.
But she said: "People should be aware that migraine is never triggered by one thing on its own. They need to be aware of other triggers and even if the weather is a trigger for them, they can still avoid attacks by being careful about other things that they do."
She said other common triggers to be aware of were missed meals and lack of sleep.
"Don't put all your triggers together. If you have one that you are becoming aware of, do something to compensate," she said.
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