Major Finding: Increases in the outdoor environmental pollutants carbon monoxide, nitrogen dioxide, particulate matter, and sulfur dioxide each were associated with increases in the frequency, severity, or medical consultation rates for headache or migraine.
Data Source: Review of 11 studies of air pollution and headache conducted in North and South America and Europe between 1988 and 2009.
Disclosures: Dr. Cardona said that he and his coauthors have no relevant conflicts of interest.
LOS ANGELES – Increases in five air pollutants each were linked with increased frequency, severity, or medical consultation rates for headache or migraine in a review of 11 studies from three continents.
The increased risk for headaches is not sufficient to recommend lifestyle changes for individuals on days of high air pollution solely because of the headache risk, but the impact on public health could be large because headache and migraine are prevalent and air pollution is common, Dr. Luzma Cardona said at the meeting.
The U.S. Environmental Protection Agency sets air quality standards for six “criteria” pollutants – carbon monoxide, nitrogen dioxide, particulate matter less than 10 microns in size (PM10), particulate matter less than 2.5 microns in size (PM2.5), sulfur dioxide, and lead. High-quality monitoring data on these pollutants are available in many developed countries.
Dr. Cardona and her associates analyzed all studies between 1988 and 2009 in North and South America and Europe that looked at links between these pollutants and headache or migraine. Five of the six pollutants were significantly associated with headache or migraine in more than one study; none of the studies compared outdoor levels of lead and headache. The strongest, most consistent pairing was between nitrogen dioxide and migraine, which were significantly associated in 7 of 11 studies. Sulfur dioxide was significantly associated with “headache not otherwise specified” in 4 of 11 studies, reported Dr. Cardona of the department of neurology at Brigham and Women's/Faulkner Hospital, Boston.
The researchers could not summarize the data quantitatively because of differences between the studies in methods, end points, and outcomes. Of the 11 studies, 2 used symptom diaries to track headache incidence, duration, or severity; 2 looked at medical house calls because of headache; 6 studied emergency department visits; and 1 assessed hospital admissions for headache.
For example, one study in Chile found that the risk of hospitalization for migraine increased 10%–11% for every 1-ppm increase in carbon monoxide, every 29-mcg/m
In several studies, temperature, humidity, and barometric pressure affected the relationship between pollutants and headache.
Air pollutants might serve as low-level irritants of structures innervated by the trigeminal nerve or trigger headache through other mechanisms, Dr. Cardona noted.