More people go to the emergency room for headache treatment in warm weather, researchers report.

Scientists examined seven years of records of more than 7,000 people with a primary diagnosis of headache seen in a hospital emergency room in Boston. Then they checked data on temperature, humidity, barometric pressure and air pollution during the three days before each visit. The study appears in the March 10 issue of Neurology.

For each rise of 5 degrees Celsius, the researchers found, the risk of a headache requiring emergency-room treatment rose 7.5 percent. There was a weaker association with lower barometric pressure, but only for nonmigraine headaches. There was no connection between headache frequency and air pollution levels in the days before emergency visits, except for a slightly higher risk for nonmigraine headaches on days of high nitrogen dioxide readings.

Why higher temperatures would cause more headaches is not clear, according to the lead author, Dr.Kenneth J.Mukamal, an associate professor of medicine at Harvard University.

“There are some physiological effects of warm weather - blood pressure tends to be lower, for example - but how that would cause headaches is uncertain.”

Still, Dr.Mukamal added,“it is important to identify triggers for headaches, and this may be one of them.”


NICHOLAS BAKALAR