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01:15 - Source: CNN
CNN  — 

Exposure to air pollution may be tied to the risk of developing depression later in life, a large new study finds.

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

Depression itself is a serious health condition. When it develops in an older adult, it can also contribute to problems with the ability to think clearly, studies show, as well as physical problems and even death.

Previous research has found that a new diagnosis of depression is less common among older adults than in younger populations.

“That’s one of the biggest reason we wanted to conduct this analysis,” said Dr. Xinye Qiu, co-author of the new study, published Friday in JAMA Network Open. Qiu is a postdoctoral research fellow in the Department of Environmental Health at Harvard T.H. Chan School of Public Health. “Surprisingly, we saw a large number of late-onset depression diagnoses in this study.”

The researchers looked at information on more than 8.9 million people who got their health insurance through Medicare and found that more than 1.52 million were diagnosed with depression later in life during the study period of 2005 to 2016. But the number is probably an undercount; studies show that late-in-life depression is often underdiagnosed.

To determine the study participants’ pollution exposure, Qiu and her co-authors looked at where each of the people diagnosed with depression lived and created models to determine the exposure to pollution at each ZIP code, averaged across a year.

The researchers looked at the study participants’ exposure to three kinds of air pollution: fine particulate matter, also known as PM2.5 or particle pollution; nitrogen dioxide; and ozone.

Particle pollution is the mix of solid and liquid droplets floating in the air. It can come in the form of dirt, dust, soot or smoke. Coal- and natural gas-fired power plants create it, as do cars, agriculture, unpaved roads, construction sites and wildfires.

PM2.5 is so tiny – 1/20th of a width of a human hair – that it can travel past your body’s usual defenses.

Instead of being carried out when you exhale, it can get stuck in your lungs or go into your bloodstream. The particles cause irritation and inflammation and may lead to respiratory problems. Exposure can cause cancer, stroke or heart attack; it could also aggravate asthma, and it has long been associated with a higher risk of depression and anxiety.