Air pollution is associated with increased migraine activity, according to a study published in Neurology. Both short-term and cumulative exposure to air pollution as well as climate factors such as heat and humidity were associated with increased migraine activity.
The study does not prove that air pollution causes migraine attacks; it only shows an association.
“These results help us to better understand how and when migraine attacks occur,” said study author Ido Peles, MD, of Ben-Gurion University of the Negev in Be’er Sheva, Israel.
“They suggest that for people who have a susceptibility to migraine to begin with, environmental factors may play two roles: intermediate-term factors such as heat and humidity may modify the risk for attacks, while short-term factors such as spikes in pollution levels may trigger attacks.”
How the long-term study was done
The study involved 7,032 people with migraine who lived in Be’er Sheva in the Negev desert and were followed for an average of 10 years.
Researchers looked at daily exposure to air pollution from traffic, industry and dust storms, as well as weather conditions. Then they looked at how often and when people had to visit the hospital or a primary care office with an acute migraine and compared that to the pollution and weather conditions that day and up to seven days earlier, since pollution effects may take a few days to affect the body.
They also looked at cumulative exposure to air pollution and migraines. As another measure of migraine activity, researchers checked pharmacy records to see how many doses of the migraine medications, called triptans, participants needed.
What the migraine data revealed
During the study, 2,215 people, or 32%, had at least one visit to the hospital or clinic for acute migraine. A total of 47% of the people had purchased triptan medications during the study, with average use at two tablets per month and 2.3% of people using 10 or more tablets per month.
The researchers found an association between air pollution and visits to the hospital or clinic for migraine.
On the day with the highest number of visits to the hospital or clinic, air pollution levels were elevated compared to the average amount over the study period. On that day, the level of particulate matter 10, or PM10, which includes dust, was 119.9 microns per square meter (µm/m3), compared to an average of 57.9 during the study.
For PM2.5, which includes particles from motor vehicle exhaust and the burning of fuels from power plants and other industries, the level on that day was 27.3 µm/m3, compared to an average of 22.3 during the study. For nitrogen dioxide, or NO2, a gas mostly from traffic emissions, the level on that day was 11.2 parts per billion, compared to an average of 8.7.
The day with the fewest visits to the hospital or clinic also had lower than average pollution levels.
Pollution types and relative risks
After adjusting for other factors that could affect the risk of migraine attacks, such as sex and socioeconomic status, researchers found that people with short-term exposure to high levels of NO2 were 41% more likely to go to the hospital or clinic for migraine than people not exposed to high levels.
People exposed to high levels of solar radiation, or ultraviolet (UV) rays from the sun, were 23% more likely to seek help for migraine than those not exposed to high levels.
People with cumulative exposure to high levels of NO2 were 10% more likely to have high use of migraine drugs than people without cumulative exposure to high levels. People with cumulative exposure to high levels of PM2.5 were 9% more likely to have high use of the drugs.
Researchers found that climate conditions played a role in the effects of pollution. High temperatures and low humidity amplified the effect of NO2, while cold and humid conditions intensified the effect of PM2.5.
Implications for care and prevention
“These findings highlight opportunities for anticipating what care will be needed,” Peles said. “As climate change intensifies the frequency of heat waves, dust storms and pollution episodes, we will need to integrate these environmental risk factors into our guidance for people with migraine.
“When high-risk exposure periods are in the forecast, doctors can advise people to limit their outdoor activity and use air filters, take short-term preventative medications and start using their migraine drugs at the first sign of a problem to ward off attacks.”
Study limitations and who it reflects
A limitation of the study is that exposure to air pollution was measured by monitoring stations and did not take into account individual behaviors such as amount of time spent indoors, use of air conditioning or air filters, type of job and daily activities.
In addition, since the information on migraine activity was gathered through hospital and clinic visits and pharmacy data, the findings mainly reflect people with severe migraine and may not be applicable to people with milder episodes of migraine or those they manage on their own.