Polluted air causes headaches

High levels of air pollution may cause headaches.

Short and long-term exposure to air pollution in cities  North America and Europe has been associated with increased respiratory symptoms, hospitalization and even death from cardiac and respiratory diseases. Headache is a common symptom and among the many self-reported triggers for migraines are weather, fatigue, stress, food, menstruation, and infections. There have, however, been few studies of the effect of air pollution on headache.

Researchers assessed air pollution levels taken at 7 monitoring stations in Chile (a densely populated region surrounded by the Coastal and Andes mountains and, therefore, geographically prone to air pollution) between 2001 and 2005. The stations measured for ozone and air pollutants such as nitrogen and sulfur dioxide, carbon monoxide, and tiny, floating particles known as particulate matter associated with the combustion of gasoline, natural gas, and other fossil fuels. The researchers also collected information on the number of hospitalisations for migraine headache, as well as tension, cluster, or other types of headaches.

It was found that air pollution was a risk factor for all types of headaches, with migraine being the type most consistently associated with individual air pollutants. This remained true in all pollutant-headache combinations analysed and these associations did not significantly change in analyses that accounted for the influence of age, gender or season.

Also, there were increased hospital admissions for migraines and other headaches on days of elevated air pollution readings. With the exception of ozone, it was difficult for the researchers to isolate the effect of 1 pollutant from that of the others due to their common source, fossil fuel combustion. However, for migraine, the effect of nitrogen dioxide,  a good marker for mobile combustion sources or urban traffic, was independent of each of the other pollutants. Whether nitrogen dioxide per se contributes to headache directly or is simply the best marker of exposure to other toxic pollutants could not be determined.

Noxious stimuli are known to trigger headache, and neural and blood vessel changes are thought to be important in the causation of headache. Sulfur dioxide and ozone are irritants, and air pollution influences neural and vascular activity.

The researchers say that further studies are required in different geographic regions to test these findings before recommending that headache sufferers remain indoors on days with high air pollution levels.