A study to be published in Tuesday's issue of the journal Neurology suggests rising temperatures bring on headaches. Wilfredo Aguilar wipes sweat from his forehead as he takes a break from painting a building under the hot sun on Hollywood Boulevard in Los Angeles on June 19. (Kevork Djansezian/Associated Press)

Higher temperatures not only prompt people to seek shade, but the rising mercury might also bring on headaches, a large-scale study suggests.

In a study to be published in Tuesday's issue of the journal Neurology, researchers looked at 7,054 people who went to emergency rooms in Boston over six years and were diagnosed with headache.

Scientists compared temperature levels, barometric pressure, humidity and other weather or air pollution factors during one to three days leading up to the hospital visit.

'As lovely as the weather can be … I'm in my bed, holding my head in agony.'— Headache sufferer Lauren Hancock of Calgary

The risk of headache went up by about 7.5 per cent for every five-degree Celsius increase in temperature, reported Dr. Kenneth Mukamal of the Beth Israel Deaconess Medical Center and Harvard medical school in Boston and his colleagues.

"Air temperature and pressure have been widely cited as a possible trigger for headaches, particularly migraines, but the potential connection hasn't been well documented," said Mukamal, an internist.

The study found that changes in barometric pressure had much less of an effect.

The study was designed to compare weather and air pollution conditions right before an emergency visit, with those same factors measured earlier and later the same month.

Air pollution levels such as fine particulate matter and sulphur dioxide had no effect on the risk of headache in this study, although previous research suggest they might be a stroke trigger.

Avoiding weather-related headaches

While the magnitude of increased risk is modest and may not be important in caring for individual patients compared with other potential migraine and headache triggers, the public health impact could be large since everyone who lives in a given geographic area is exposed, the researchers said.

The findings suggest that something is happening in the autonomic nervous system that regulates internal organs, Mukamal said.

It's difficult to apply the results of the study, since most people with migraines never go to emergency, the researchers acknowledged.

Lauren Hancock, 25, lives in chinook country, where Calgary's winter temperatures can shoot up dramatically.

"As lovely as the weather can be when you're in the middle of December and people are jogging in their shorts and t-shirts, I'm in my bed, holding my head in agony," Hancock said.

Limit medication use

Mukamal recommended that people with headaches sit down with their doctors to identify triggers that lead to headache symptoms since doctors might be able to prescribe medications to help avert the onset of weather-related headaches.

Hancock said she's not sure how much help it would be knowing when the migraines are coming, because she only takes her medication when the pain is severe.

Some people take prophylactic medications for months at a time to prevent attacks. But other kinds of migraine medications should not be taken too frequently, said Dr. Werner Becker, a professor in the department of clinical neurosciences at the University of Calgary.

"If patients take their medication more than 10 days a month they become at risk for getting more and more migraines," Becker said.

Dr. John Bart is a family physician in Toronto who has studied the link between weather and all sorts of medical ailments. He also runs a website called Mediclim that warns people when weather changes might bring on their symptoms.

Bart said he believes a combination of weather factors is involved, and the subject needs more study.

About 18 per cent of women and six per cent of men in the U.S. say they have migraines, particularly young and middle-aged adults, the team noted. The annual cost attributed to migraines is estimated at $17 billion US.

The study was supported by the U.S. National Institute of Environmental Health Sciences and the U.S. Environmental Protection Agency.

With files from the Canadian Press