High temperatures and low air pressure trigger migraines, according to a large study published online today in the journal Neurology. But researchers did not find a clear association between headaches and air pollution.
Weather -- especially changes in air pressure -- is frequently cited as a headache trigger but it had not previously been shown in such a large, well-designed study.
The researchers, from Boston's Beth Israel Deaconess Medical Center and the Harvard School of Public Health, were curious about pollution because fine particulate pollutants cause or complicate other health problems, including heart attacks, stroke, congestive heart failure and asthma.
The study included 7,054 headache patients of both genders and varying ages and ethnic groups who were seen at the medical center's emergency room between May 2000 and December 2007. Researchers looked at temperature levels, barometric pressure, humidity, fine particulate matter and other pollutants during the three days before each patient was seen in the ER and for a control day, in which the patient did not report a headache.
A rise in temperature was strongly associated with headaches: An increase of 5 degrees Celsius (9 degrees F, as a reader has so kindly pointed out below) increased the risk of migraine by 7.4%. Low air pressure, which often precedes storms, played a smaller role.
"This study provides pretty rigorous scientific proof that changes in temperature are migraine triggers, and that's something that's not been known before," said Dr. Richard Lipton of the Montefiore Headache Center in New York City.
Knowing what can trigger an attack gives migraine sufferers a measure of control, said Lipton, who was not associated with the study. One of his patients, for example, moved from New York City to Arizona because air pressure in the Southwest is less changeable.
Triggers often work in concert. So migraine sufferers could, for example, be especially careful to avoid red wine and chocolate on hotter days or when a storm is forecast.
Lipton was less convinced by the study's finding on ambient air pollution, which, he said, was harder than temperature to measure over a large region. But he also said that a similar study that found a correlation between particulate matter and asthma also used a central monitoring site.
The migraine study did find a borderline association between headaches and levels of nitrogen dioxide, found in smog and car exhaust. Given the role of fine particulate matter in cardiovascular disease, the researchers called for additional study on its relation to migraines.
-- Mary Engel
Photo credit: Janet Morgan Mol / Novartis Pharmaceuticals