Air Pollution Linked to Depression and Suicide Risk in Study

Exposure to air pollution has been linked to an increased risk of suicide and depression in a study.

Researchers reviewed nine existing studies on 16 countries, which examined the potential link between air pollution and depression, anxiety, bipolar disorder, psychosis and suicide. The sample sizes in the studies ranged from 958 to 69,966 participants.

The researchers found a link between being in contact with PM2.5—or particulate matter measuring up to 2.5 micrometers in diameter—for at least six months. To give an idea of the size, human hair measures between 40 to 120 micrometers. The researchers defined this as long-term exposure. A 10 microgram per metre cubed spike in the average level of long-term PM 2.5 was linked with a 10 percent increase in the likelihood of experiencing depression.

They also found an association between short-term exposure to PM 10—or particulate matter measuring up to 10 micrometers in diameter—and suicide. The risk of suicide rose by 2 percent for each 10 microgram per metre cubed increase of PM10 over the course of three days.

Sources of PM 10 and 2.5 include fossil-fuel-powered cars, dust from industrial activities, and wood burning and forest fires.

More research is needed to confirm whether pollution causes poor mental health, the authors wrote in the journal Environmental Health Perspectives.

Co-author Isobel Braithwaite of the UCL Psychiatry and UCL Institute of Health Informatics departments told Newsweek if proven, this link could "potentially be affecting millions of people."

Depression affects more than 260 million people worldwide, she highlighted, and around 90 percent of people worldwide breathe air pollution levels above World Health Organization guidelines.

"There are a number of studies that have found evidence of biological changes which may help to explain the mechanisms which could underlie this, such as inflammation within the brain, damage to nerve cells and changes in stress hormone levels, but we need more research to help clarify the roles that these may play," said Braithwaite.

Past studies have found links between air pollution and dementia risk, as well as some developmental disorders, explained Braithwaite. But only a small number have looked at mental health problems.

Braithwaite said the study has two main limitations. The team couldn't be certain all the relevant evidence on the topic had been published, as it is easier for studies which find a positive association to get published than those which don't. In addition, the research carries the limitations of the individual studies used.

"Given what we know about the wider health risks of being exposed to air pollution, the fact that it may also be linked with depression strengthens the case for people to reduce their own contribution to air pollution, and to call for better public policies to reduce it," said Braithwaite.

"So, in addition to actions like walking, cycling or taking public transport rather than driving, people who are concerned may want to consider how they can persuade decision-makers to make cleaner air in our cities and towns a top priority," she said.

However, John Ioannidis, professor of medicine and of epidemiology and population health at Stanford University who did not work on the research, told Newsweek he was "not convinced by the presented data that air pollution itself increases the risk of depression and of suicide."

He said most of the studies done to date on the topic have very large levels of uncertainty. "Putting them together in a meta-analysis reduces this uncertainty somewhat, but may give some false reassurance that we know more than we really do," argued Ioannidis.

He said air pollution is "clearly bad for your health for many other reasons," including heart and respiratory disease and an increase in the overall risk of dying prematurely.

"The risk of depression and suicide is very small, even if real (which I doubt), so people should not worry about this risk in particular," he said.

Citizens should put pressure on governments to act on air pollution, he said.

"These problems need to be tackled at the level of public policy and regulation. There is very little a citizen can do himself or herself and obviously it makes no sense to tell people to move elsewhere or to try to protect themselves by not being exposed to air!"

"I worry that by trying to expand the range of diseases that are putatively associated with air pollution, we forget that air pollution is already proven to be bad in major ways, including death risk. Instead of acting on it, we may end up asking for more research, wasting valuable time," he argued.

Atif Khan, a scientist in the Department of Medicine at the University of Chicago, who also didn't work on the paper, expressed similar concerns about the studies used. He told Newsweek the research could inspire others to conduct well-designed experimental studies.

Similarly to Ioannidis, Khan argued: "the evidence piles up on causal association between air pollution and depression, there shouldn't be any harm in thinking of and taking measures to reduce the air pollution and improve the air quality."

If you have thoughts of suicide, confidential help is available for free at the National Suicide Prevention Lifeline. Call 1-800-273-8255. The line is available 24 hours, every day.

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A stock image shows cars in a traffic jam. Researchers have looked at the potential link between pollution and mental illness. Getty