When most people think about the risks associated with air pollution, respiratory issues are the first that come to mind. In fact, in 20161 outdoor and inside air pollution contributed to respiratory infections resulting in 543,000 deaths in children under 5. However, the respiratory system is not the only one affected by this.
The World Health Organization reported on published studies from dozens of top experts, which revealed some of the health risks for children that are associated with air pollution. These included obesity, asthma, childhood cancers, infant mortality and adverse birth outcomes. Evidence also suggests exposure before birth increases the risk of cardiovascular and lung disease later in life.
A study by the American Thoracic Society2 that was presented at the 2017 International Conference suggested air pollution may also reduce sleep quality. There are a number of health repercussions associated with sleep deprivation and poor quality sleep.
These include an increased risk of accidents,3 cardiovascular disease,4 high blood pressure,5 cancer6 and osteoporosis.7 Researchers have also investigated the bidirectional relationship between sleep and depression, finding that when sleep quality improves, it lessens depression symptoms.8
Global Studies Link Air Pollution to Suicide and Depression
Air pollution is measured by the size of the particulate matter. Fine particulate matter measures less than 2.5 micrograms (PM2.5) in diameter and is a good indicator of outdoor air pollution. PM2.5 is the focus of many studies.
The particles are important as they are small enough to be inhaled into the lungs and absorbed into the bloodstream.9 Once in your body they may deposit in any organ system, including the brain. In recent research, scientists have associated acute exposure to PM2.5 with increased psychiatric emergency room visits for children who are having anxiety and/or have attempted suicide.10
In a meta-analysis of recent studies by a team from Cambridge University11 it was found that elevated exposure to PM2.5 yielded a 19% increase in the risk of depression for children, as well as a small increased risk for suicide. They evaluated results from 14 studies and 684,859 participants and determined that PM10 was not linked to depression or suicide, indicating the particulate matter may be too large to be absorbed into the bloodstream and affect the brain.
However, in a separate analysis of data from 16 countries researchers reported that an increase in PM2.5 and PM10 was associated with depression and increased numbers of suicide.12
The systematic review and meta-analysis13 was published in December 2019 in Environmental Health Perspectives. One study author, Isobel Braithwaite from University College of London, commented on the results:
"We already know that air pollution is bad for people's health, with numerous physical health risks ranging from heart and lung disease to stroke and a higher risk of dementia. Here, we're showing that air pollution could be causing substantial harm to our mental health as well, making the case for cleaning up the air we breathe even more urgent.
We found quite consistent results across the studies we reviewed that analysed the relationship between long-term air pollution exposure and depression, even after adjustment for many other factors which could explain the association. The association seems to be similar in magnitude to those that have been found for some physical health impacts of particulate matter, such as all-cause mortality."
Meeting EU Pollution Limit May Have Global Effect
There was also a connection between PM10 particulate matter exposure and the number of suicides reported in the studies. Researchers found the risk was significantly higher on days after a three-day period when levels of PM10 were higher, rather than after less polluted time periods.
In these studies, confounding factors such as weather changes and the day of the week did not account for short-term changes in suicide risk, nor did socioeconomic factors or neighborhoods. The evidence was stronger for suicide with PM10 and less for depression. Another study author, Joseph Hayes, said:
"Our findings correspond with other studies that have come out this year, with further evidence in young people and in other mental health conditions. While we cannot yet say that this relationship is causal, the evidence is highly suggestive that air pollution itself increases the risk of adverse mental health outcomes.
A lot of what we can do to reduce air pollution can also benefit our mental health in other ways, such as enabling people to cycle or walk rather than drive, and enhancing access to parks, so this adds support to the promotion of active travel and urban green spaces."
The scientists hypothesized that if the relationship were causal, the global risk of depression could go down by 15% if exposure was reduced from PM 2.5 from 44 µg/m3 to 25 µg/m3. The global levels of PM 2.5 ranged from 114 µg/m3 in Delhi to 6 µg/m3 in Ottawa, Canada.
Within the U.K., they found the average level was 12.8 µg/m3. The WHO recommends a limit of 10 µg/m3, which the researchers estimated could reduce the risk of depression by about 2.5%. While the goal of the WHO is 10 µg/m3, even meeting the less stringent EU guideline of 25 µg/m3 could have a significant global impact on mental and physical health. Braithwaite went on to say:14
“We know that the finest particulates from dirty air can reach the brain via both the bloodstream and the nose, and that air pollution has been implicated in increased [brain] inflammation, damage to nerve cells and to changes in stress hormone production, which have been linked to poor mental health.”