Depression, suicide risk, linked to air pollution

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People exposed to higher levels of air pollution are more likely to experience depression or die by suicide, according to new research from the University College London in England, which was published in the journal Environmental Health Perspectives.

For the study, researchers conducted a systematic review and meta-analysis of evidence connecting air pollution and a range of mental health problems.

The researchers found that, if the relationship with depression reported in some of these studies is causal, then reducing global average exposure to fine particulate matter (PM2.5) air pollution from 44 micrograms per meter cubed (μg/m3) to 25μg/m3 could result in a 15 percent reduction in depression risk worldwide.

The World Health Organization guidelines recommend that fine particulate matter pollution, small airborne particles that can include dust and soot, should be kept under 10μg/m3.

The research team searched for studies that had investigated the association between particulate matter pollution and five different adverse mental health outcomes in adults. They identified 25 studies that fitted their criteria, nine of which were included in the primary analyses.

Five studies looking at long-term particulate matter exposure and depression were included in one meta-analysis. By pooling the results, they found that a 10μg/m3 increase in the average level of fine PM2.5 air pollution people were exposed to over long periods was associated with an approximately 10 percent increase in their odds of depression.

The researchers also found evidence of a connection between short-term changes in coarse particulate air pollution (PM10) exposure and the number of suicides, from pooling the results of four different studies in a meta-analysis. The risk of suicide appears to be measurably higher on days when PM10 levels have been high over a three-day period than after less polluted periods.

The studies into short-term changes in suicide risk accounted for confounding factors such as weather changes, and day of the week. The relationship is not affected by other neighborhood or socioeconomic factors given that the comparisons being made are among the same individuals on days with different pollution levels.

The researchers said the evidence was particularly strong for the suicide risk link, but the effect was smaller than for depression, an increase in suicide risk of 2 percent for each 10μg/m3 increase in the average coarse particulate pollution level over a three-day period.

Additionally, researchers said they cannot yet confirm whether air pollution directly causes mental ill health but say there is evidence to suggest possible causal mechanisms. The researchers said they hope to follow up their study with further research into indoor air pollution and mental health risks.