Long-term exposure to pollution leads to depression

Exposure to air pollution may be linked to the risk of developing depression later in life, according to a new study. Two new studies add to mounting evidence about the dire effects of pollution on mental health. These investigations revealed that long-term breathing of polluted air carries an increased risk of depression.

Scientists are finding increasing evidence that people who live in polluted areas are at higher risk of depression than those who live with cleaner air. But this study published in JAMA Network Open is one of the first to examine associations between long-term exposure and the risk of depression diagnosed after age 64.

Although previous research had found that the diagnosis of depression is less frequent in older adults, the truth is that it can contribute to problems such as the ability to think clearly, as well as physical conditions and even death.

"That's one of the main reasons we wanted to do this analysis," said Xinye Qiu, a co-author of the new study and a postdoctoral researcher in the Department of Environmental Health at the Harvard TH Chan School of Public Health. "Surprisingly, we saw a large number of diagnoses of late-onset depression in this study."

Researchers analyzed data from more than 8.9 million people who obtained their health insurance through Medicare and found that more than 1.52 million were diagnosed with depression later in life during the study period from 2005 to 2016.

More pollution, more cases of depression

Another second study published in the same journal has also obtained results along the same lines: long-term exposure to even low levels of air pollutants was associated with a higher incidence of depression and anxiety.

Researchers from Great Britain and China examined the relationship between prolonged exposure to multiple air pollutants and occurrences of depression and anxiety.

They followed a group of about 390,000 people, mostly residents of Great Britain, for 11 years and found an increased risk of depression and anxiety, even when air pollution levels were below British air quality standards.

These works used a database of Medicare, the public health insurance reserved for older people in the United States, and studied a population of about 8.9 million people, of whom 1.5 suffer from depression.

The results again showed a strong association between pollution and depression, particularly when looking at fluxes of fine particles and nitrogen dioxide for disadvantaged populations.

The three air pollutants studied were

To determine the pollution exposure of the study participants, Qiu and her team looked at where each of the people diagnosed with depression lived and created models to determine the pollution exposure in each ZIP code, averaged over a period of time.

They then looked at the study participants' exposure to three types of air pollution: fine particulate matter (also known as PM2.5), nitrogen dioxide, and ozone.

• Fine particles are tiny particles like those that can make the air look hazy when pollution levels are high.

• Ozone, also known as smog, comes from sources like exhaust pipes and chimneys.

• Nitrogen dioxide is among the group of gases that are formed when fossil fuels such as coal, oil, gas, or diesel are burned.

In this way, they discovered that people who lived in areas with higher levels of pollution had a greater risk of being diagnosed with depression in the long term. The three pollutants studied were associated with a higher risk of late depression, even with lower pollution levels.

"So there is no real threshold, which means that future societies will have to remove this pollution or reduce it as much as possible because it carries a risk," Qiu said.

According to the study, older adults with underlying heart or respiratory problems were also more likely to develop depression at the end of their lives when exposed to nitrogen dioxide pollution.

The results suggest harmful associations between long-term exposure to air pollution and increased risk of depression, anxiety, and depression in later life. In turn, that reductions in this exposure could alleviate the burden of both diseases.

Physical and mental pathologies

It is important to know that the link between pollution and disease is made through associative studies and long-term research that finds that the disease rate in contaminated areas is higher than in other areas.

These studies are of the epidemiological type and have been carried out in different parts of the world, such as China, the United States and several in England.

Cognitive impairment and diagnoses such as depression or anxiety are part of the new studies. In the last few days, two investigations have associated pollution with an increased risk of mental disorders.

The studies are due, in part, to the limited epidemiological evidence about the relationship between pollution and mental health, specifically episodes of anxiety, depression, and geriatric (late-life) depression.

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