LOS ANGELES – Exposure to air pollution might be linked to suicide risk, investigators in Salt Lake County, Utah, suggest.
Using the Environmental Protection Agency’s air data Web site, Amanda V. Bakian, Ph.D., and her associates checked air quality in the 3 days leading up to each of the 1,546 suicides in the county from 2000 to 2010, dividing the concentration of pollution into quartiles. They found a 20% increase in suicide risk between the lowest and highest quartiles of nitrogen dioxide (adjusted odds ratio, 1.20; 95% CI, 1.04-1.39), and a 5% interquartile risk increase for fine particulate matter (AOR, 1.05; 95% CI, 1.01-1.10).
The finding was not surprising; suicide risk has been linked to particulate matter in both Taiwan and South Korea, but "it’s interesting that we see consistent findings for areas that are vastly different culturally, meteorologically, and geographically," said Dr. Bakian of the department of psychiatry at the University of Utah, Salt Lake City, lead investigator of the study.
Amanda Bakian, Ph.D.
What was surprising was that the risk was not worst in the winter, when temperature inversions are most likely to trap air pollution in the area’s valleys. Instead, suicide risk was greatest in the spring after exposure to high levels of fine particles (AOR, 1.28; 95% CI, 1.00-1.61), and in the spring/fall transition after exposure to high levels of nitrogen dioxide (AOR, 1.34; 95% CI, 1.09-1.66).
"I was surprised we didn’t find peak association in winter. [Perhaps,] air pollution is interacting with other springtime risk factors for suicide, such as pollen and maybe mood disorders; we see suicide peaks in the spring for individuals with mood disorders," Dr. Bakian said.
"We didn’t design the study to test cause and effect, so we cannot say that air pollution causes suicide. The study was only designed to look for a relationship between the two," she said. Next up, the team plans to review patient-level data, including psychiatric histories and socioeconomic status.
Air pollution exposures are tied to cognitive deficits, oxidative stress, neuroinflammation, and neurodegeneration (Exp. Toxicol. Pathol. 2013;65:503-11). Fossil fuels are the primary source of both fine particulate matter and nitrogen dioxide. Indoor sources of fine particles include tobacco smoke, fuel-burning space heaters, and cooking.
If the link to suicide proves real, Dr. Bakian suggested oxidative stress or hypoxia as two possible explanations. In the meantime, "air pollution is a modifiable risk factor; people can reduce their exposure." Besides environmental clean-up, face masks and indoor air filters might help, she said.
The team found no suicide link for atmospheric concentrations of coarse particulate matter and sulfur dioxide.
Dr. Bakian has no relevant disclosures. The work had no outside funding.