Hot weather a migraine 'trigger'
A hot day can spell bad news for migraine sufferers, increasing their risk of an attack the next day, US research suggests.
The risk went up by 7.5% for every five degree Celsius increase in temperature revealed the study of more than 7,000 patients, published in Neurology.
The same applied to people who suffer from non-migraine headaches too.
Although you can't alter the weather, people can watch the forecast and pop a pill to avert attacks, the authors say.
As well as temperature, people might want to check air pressure too, as lower barometer readings over the past couple of days were also linked with migraines, although less strongly.
The study looked at people attending the emergency department of a large US hospital for advice about a headache at any point during a seven year period.
Overall, 2,250 were diagnosed with migraine and 4,803 with "tension" or "unspecified" headaches.
Using meteorological and pollutant monitors, the researchers then compared measurements of a number of environmental factors during the days leading up to and again some weeks after a patient's hospital visit.
When they averaged the temperature for the day, taking into consideration night time lows and midday highs, the researchers found every five degree Celsius rise in temperature was linked to a 7.5% hike in headache risk.
Lower barometric air pressure, which typically brings cloudy or stormy skies, within two or three days leading up to a person's hospital visit also increased headache risk.
Air pollution had no effect.
Researcher Dr Kenneth Mukamal, of the Beth Israel Deaconess Medical Center, said: "These findings help tell us that the environment around us does affect our health and, in terms of headaches, may be impacting many, many people on a daily basis."
He said headache patients should see their doctor to identify the triggers that lead to their symptoms.
Dr Brendan Davies, consultant neurologist and spokesman for the Migraine Trust, said: "This adds scientific validity to what we have suspected for some time. Up to 50% of patients believe weather may trigger their migraine.
"It looks like it is the change in the air temperature, and to a lesser extent the change in air pressure that is important.
"It would be interesting to see if the same environmental factors apply to workers in an office. It also adds more to our understanding that migraine is a sensitivity problem."
He warned that people should not become over-reliant on medication, taking it just in case.
"This does not mean that just because there is a hot day people are going to have a migraine the next day, although it is more likely. We do not want people taking too many painkillers too often because that carries its own risks."
Professor Peter Goadsby, from the University of California, San Francisco and Institute of Neurology, London, said: "The challenge for clinical science is to link this seemingly odd trigger to the brain mechanisms involved in migraine."
Lee Tomkins, director of Migraine Action, said: "Although the study has some flaws, including the fact that most people with headache would not attend a casualty department, this study is very interesting in demonstrating how weather conditions can adversely affect migraine.
"It is another example of science 'catching up' with the anecdotal evidence that many of our members give us about everyday living with migraine."