For many years, scientists have reported intriguing links between climate or weather factors and mental health and behavior.

A provocative new study expands this field to assess effects of air pollution as well as those of climate and weather on mental health.

Specifically, the scientists have linked suicides not just with early summer and barometric pressure, but with air pollutants such as particulate matter, sulfur dioxide, and ozone, according to a study in the March Journal of Affective Disorders.

This study is both "fascinating" and troubling, Lise Van Susteren, M.D., a Washington, D.C., psychiatrist and environmental activist, told Psychiatric News. "As if the impact of environmental degradation on people's bodily health isn't disturbing enough, it now seems that we have compelling evidence of a direct psychological impact as well. Let us hope that more studies such as this one will persuade our lawmakers to let go of any ideological differences in favor of science-based policies that are healthy for us, the environment, and future generations."

Leading the new study was Albert Yang, M.D., an attending psychiatrist at Chu-Tung Veterans Hospital and lecturer in medicine at the National Yang-Ming University in Taiwan. Yang and his colleagues obtained data about suicides in Taipei, Taiwan, over an 18-year period (from 1991 through 2008) from the Taipei City Government Department of Health, data about weather in Taipei during the period from Taiwan's Central Weather Bureau, and data about air pollution from Taiwan's Environmental Protection Administration.

The researchers then looked to see whether they could link the 4,857 suicides in Taipei during this period with specific weather variables or air pollutants in Taipei over the same period.

One of the mathematical tools they used in their evaluation was empirical mode decomposition (EMD), an algorithm that can identify oscillations in a complex signal. It has been used by a number of disciplines, not just psychiatry. EMD was developed by the study's senior investigator, Norden Huang, Ph.D., when he worked for the U.S. National Aeronautics and Space Administration (NASA). Today Huang is affiliated with the National Central University in Taiwan.

Yang and his colleagues found not just that suicides increased during early summer, but that early summer was a time of decreasing barometric pressure and increasing particulate matter. Moreover, they discovered that while the decrease in barometric pressure lagged a little behind the increase in suicides, the increase in particulate matter preceded it. They likewise linked the number of suicides with several air pollutants—sulfur dioxide and ozone—over long time spans (two to 10 years for sulfur dioxide and 10 years for ozone).

Although the associations they demonstrated do not prove causation, Yang and his colleagues nonetheless suspect that weather and air pollutants might play a causative role in suicides. In their paper, they suggested several routes by which the relationship might unfold.

For example, animal studies have shown that exposure to ozone affects metabolism of the neurotransmitter serotonin in the brain. So it's possible that ozone or other air pollutants could alter the brain's neurotransmitter balance and increase a peron's risk for aggression and suicidal behavior. Indeed, ozone was especially linked with violent suicides in their study, the researchers noted.

Still another hypothesis they offered is that air pollutants might lead to suicide via an indirect route. For instance, particulate matter can provoke acute respiratory symptoms, and poor respiratory function can lead to greater suicide risk, past research has shown.

The challenge now, Yang told Psychiatric News, is to learn more about how weather or air pollution might increase suicide risk.

The findings also need to be replicated in other populations and geographic regions, Yang and his colleagues pointed out. But meanwhile, the findings seem to be "the first evidence of suicide associated with air pollution data at different time scales … [and] may stimulate a new line of research associated with suicide and environmental risk," they said.

The study was funded by the Taipei Veterans General Hospital and National Science Council of Taiwan.

An abstract of "Decomposing the Association of Completed Suicide With Air Pollution, Weather, and Unemployment Data at Different Time Scales" can be accessed at <www.sciencedirect.com/science/journal/01650327> by clicking on the March issue.