Although many people who frequently suffer from headaches often blame their pain on changing weather conditions, there has been very little scientific evidence to back up their assertions.
Now a study of more than 7,000 patients provides some of the first large-scale data on how environmental conditions influence headache pain.
The findings, published in the journal Neurology, show that warmer weather and changes in atmospheric pressure may trigger headaches, especially migraines.
The U.S. research team demonstrated that each temperature increase of 5 degrees Celsius appeared to increase the risk of severe headaches by nearly 8 per cent compared to days when the weather was cooler.
Air temperature, humidity and barometric pressure are often cited as a reason for headaches, but until now there has been little concrete evidence to back this up, said Kenneth Mukamal, who led the research team at Beth Israel Deaconess Medical Center in Boston.
His team studied men and women diagnosed with a headache or migraine at the hospital emergency room between May, 2000, and December, 2007.
They used meteorological and pollutant monitors to analyze air temperature, barometric pressure, humidity, fine particulate matter, black carbon and sulphur dioxides during the three days prior to the hospital visits and then later on.
"In other words, our study design was able to directly compare weather and air pollution conditions right before an emergency-room visit with those same factors measured earlier and later the same month," Dr. Mukamal said.
The study found that of all the environmental factors tested, higher air temperature in the 24 hours before a hospital visit was most closely associated with headache symptoms.
Lower barometric pressure also appeared to be a trigger, though the association was not as strong. There was no evidence that air pollutants played a role in sparking headaches, but bigger studies are needed to exclude this as a problem, the researchers added.
The results suggest the weekly forecast could help people ready their medication to ward off headaches.
"We wanted to find out if we could verify this 'clinical folklore,'" Dr. Mukamal said in a statement released with the study. "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."
The reason is unclear but researchers know warmer weather leads to lower blood pressure, and there is good evidence migraines are related to changes in blood flow around the brain, Dr. Mukamal added in a telephone interview.
Migraine headaches affect a large segment of the population, noted Dr. Mukamal. About 18 per cent of women and 6 per cent of men report having migraine headaches.