We have known for a long time that the environments in which we live and work have an impact on our physical health – and that things we do not even realize can hurt us, such as lead or air pollution.
Nor is it a new idea that our physical environment can also affect our mental health. In the 1930s, two sociologists noticed a striking trend among people admitted to Chicago asylums. Rates of schizophrenia, they reported, were exceptionally high among people born in disadvantaged neighborhoods. Since then, researchers have found that mental illnesses of all kinds are more common in densely populated cities than in greener and more rural areas. In fact, the Urban Design and Mental Health Center estimates that city-dwellers are at about 40% risk of depression, 20% risk of anxiety, and twice the risk of schizophrenia compared to men. inhabitants of rural areas.
Part of the burden on the mental health of urban dwellers can be attributed to social problems such as loneliness and the stress of living brazenly with thousands, if not millions, of other people. But there is something about the physical nature of cities that also seems to be putting a strain on the emotional well-being of their people. Urban living involves dealing with stressors such as air and noise pollution from traffic, construction or your neighbors. However, only recently have scientists begun to seriously study the mechanisms by which exposure to various environmental stressors could harm our mental health, said Andreas Meyer-Lindenberg, director of the Central Institute of Medicine. the mental health of Mannheim, Germany. "It's an emerging field," he says.
Meyer-Lindenberg and her research partner, Matilda van den Bosch, a researcher in environmental health at the University of British Columbia in Vancouver, recently reviewed the scientific evidence of these factors and of a certain number of other physical stressors to determine whether they contribute to depression or not. The couple searched for studies on a wide range of substances and situations that people might encounter in everyday life. They found that while many of these factors were particularly abundant in cities, they were not limited to urban environments. For example, air pollution is not limited to city boundaries. Another potential hazard is pesticides, with which farm workers in particular are in contact.
Nevertheless, a key element in improving our collective mental health will be making our cities more livable, said Meyer-Lindenberg, who published this year's findings in the newspaper. Annual Public Health Review. More than half of the world's population already lives in cities and this number is expected to reach nearly 70% by 2050.
"Globally, we are becoming more urban and neighborhoods are opening up and transforming," said Marianthi-Anna Kioumourtzoglou, assistant professor of environmental health sciences at the University Mailman School of Public Health. from Columbia, who studied the impact of air pollution on mental health. "We should consciously try to do this in ways that promote mental well-being."
The risks around us
In their analysis, Meyer-Lindenberg and van den Bosch revealed that some potential threats had been examined more thoroughly than others. For some, including pollen, there was still not enough information to show a convincing connection with depression. However, the team found a number of studies suggesting that heavy metals such as lead, pesticides, common chemicals such as bisphenol A (BPA) and noise pollution could contribute to the depression, although further research is still needed to confirm that this is the case.
The evidence condemning the air pollution was even more convincing. In addition to causing respiratory and cardiovascular problems that kill millions of people each year, this particular threat increases our risk of developing a number of psychiatric problems. The poor quality of the air has been associated with depression, anxiety and psychotic experiences such as paranoia and hearing.
In the United States, emissions of many common pollutants have declined significantly in the decades following the entry into force of the Clean Air Act. However, "the fact that levels have gone down does not mean that they are safe," Kioumourtzoglou said. "We are all breathing, so we are all exposed involuntarily." She and her colleagues found that women living in heavily polluted neighborhoods are more likely than others to report anxiety symptoms and take antidepressants.
Meyer-Lindenberg and van den Bosch also explored the potential link between urban life and depression. "Cities are an interesting case," says Meyer-Lindenberg. On average, urban dwellers have access to better health care and education than others. "Cities are therefore beneficial to most aspects of human life … it's just that mental health shows the flip side of cities." Urban areas, he says, are harmful both in because of the lack of greenery and the presence of a particularly high amount of toxic exposures such as air pollution.
This does not mean that if you live near a highway or over a bar, you are doomed to suffer from depression or anxiety. Many people thrive in the cities. And mental illnesses are caused by a complex entanglement of genetic factors and life circumstances; It is rarely possible to choose a single problem and designate it as the culprit, according to Meyer-Lindenberg. Hazards such as air pollution increase a person's overall risks, especially those who are already vulnerable for other reasons. Scientists have not yet determined how much of our physical environment affects this risk. For members of poor communities, the impact is probably particularly powerful; not only does financial stress contribute to depression, but low-income neighborhoods face disproportionate levels of air and noise pollution and lead exposure.
How exactly do these things prime the brain to depression is not entirely clear. Some problems, such as noise pollution and possibly pollen, are sufficiently aggravating to contribute to depression by constantly exhausting our mood. Our environment also harms us in ways that we are not aware of, perhaps damaging our neurons or altering the abundance of chemical messengers such as serotonin, according to Meyer-Lindenberg. Pollution of air and other substances can cause an inflammatory reaction that, over time, has adverse consequences on the brain, explains Meyer-Lindenberg. In children, exposure to these risks can also prevent the brain from developing normally.
The idea that so many things we encounter in everyday life could threaten our mental well-being is alarming. But our physical environments can also feed our mental health. Many studies have shown that our risk of depression and other psychiatric disorders is reduced, as you have guessed, by contact with nature. People are more physically active in nature and images, sounds and smells of greenery and oceans soothe and strengthen our mood.
In one experiment, scientists discovered that after a walk in the wild, people were less inclined to rumination, to the tendency to be obsessed with the mistakes and disorders that often characterize disorders such as depression and depression. 'anxiety. Walking in nature has also calmed activity in many areas of the brain involved in rumination and the response to threats to our sense of belonging or feelings that we have made a social faux pas. According to Meyer-Lindenberg, one of those areas of the brain, called the anterior perigenoid cortex of the cingulum, which is involved in the regulation of our emotions, may be the key to understanding how our environment can harm or contribute to our mental health.
"Many of the risk factors we have examined tend to affect the same brain system," he says. He and his colleagues found that this part of the brain reacts particularly strongly to social stress situations in people who are raised in the cities. This region also seems to be influenced by a number of genes related to susceptibility to depression and other psychiatric illnesses, suggesting that it might be important for our mental health.
In the United States, nearly one in five adults live with mental illness, while depression is considered the leading cause of disability in the world by the World Health Organization. It is therefore extremely important for us to learn how the world around us shapes our mental health, says van den Bosch. She hopes that this information will motivate policy makers to further tighten air pollution restrictions and other harmful products of the human industry.
"We know that many of these things are bad and do we really need more evidence? Looks like the answer is yes, "says van den Bosch. Although the effect on our overall risk of mental illness is small, she says, "It will always have a huge impact on the health of the population."
Kioumourtzoglou also hopes that research will determine whether physical, sports or other activities could offset the risks that air pollution and other hazards pose to our mental health. Whatever these steps are, they will probably not be easy or convenient for everyone. That's why it's also important to inject greenery into our cities, where many risks are most concentrated. Not only do parks and street trees provide city dwellers with an invigorating dose of nature, they also help us reduce noise and absorb pollutants.
Kioumourtzoglou admits that we can not simply flatten our cities and rebuild them into wooded utopias. But we can keep environmental health in mind when planning new neighborhoods and renovating existing neighborhoods. "Sometimes it takes time for new, more protective regulations to come into effect – and we need to know what we can do in the meantime to protect ourselves," she says.