Most of us think about air quality in terms of our lungs and our heart. If you have ever been told to stay indoors on a smoggy day, you already know that dirty air is hard on the body. But a growing pile of research suggests that the air we breathe may also reach further than we once thought, all the way to the brain. A recent scientific review looked closely at how long-term exposure to air pollution may be connected to Parkinson’s disease, a condition that affects movement and, over time, memory and thinking as well.

Scientists have been comparing communities with higher levels of air pollution to those with cleaner air, and looking at outcomes for people who already have Parkinson’s disease. Several studies have found that people who live with more soot, exhaust, and industrial particles in the air around them face a higher risk of developing Parkinson’s disease. Among people who already have the condition, heavier pollution exposure has also been linked to faster progression of symptoms and a greater chance of hospital stays.

It is worth saying plainly that not every study agrees. Some research teams have found a clear connection, while others have not found a statistically meaningful link. This is common in science when a topic is complicated, and it does not mean the concern is not real. It means researchers are still working out exactly how strong the connection is, and for whom it matters most.

One of the more interesting findings in this area of research is that Parkinson’s disease may often begin far from the brain, in the digestive system. Scientists have found that the disease is closely tied to changes in the community of bacteria that live in our gut, sometimes called the gut microbiome. A healthy gut has plenty of beneficial bacteria that help calm inflammation throughout the body. In people with Parkinson’s disease, researchers often find fewer of these helpful bacteria and more of the troublesome kind.

Here is where air pollution appears to play a role. Breathing in polluted air seems to disturb the balance of bacteria in the gut and make the lining of the intestines more permeable, sometimes described as a leaky gut. This can allow inflammation to spread through the body. Researchers believe that a specific protein in our nerve cells, called alpha-synuclein, can begin to fold incorrectly under these inflammatory conditions. Once misfolded, this protein can clump together and slowly travel from the gut up through the nervous system to the brain, where it is thought to damage the very cells that produce dopamine, a chemical the brain needs for smooth, controlled movement.

Air pollution does not only work through the gut. Some of the tiniest pollution particles, known as ultrafine particles, are small enough to travel up through the nose and settle directly in brain tissue, particularly in the area responsible for our sense of smell. Once there, they appear to trigger stress inside brain cells and disrupt the tiny power plants inside those cells, called mitochondria. Over time, this ongoing stress and inflammation can wear down the dopamine-producing neurons that keep our movements steady and coordinated.

It is important to understand that air pollution is only one piece of a much larger puzzle. Genetics, age, and other lifestyle factors all play a role in whether someone develops Parkinson’s disease.

Researchers still need larger, longer studies that track people over many years and measure their pollution exposure carefully and consistently. Without that kind of large-scale evidence, it is hard to say exactly how much any one person’s risk changes because of the air they breathe. What scientists can say with more confidence is that chronic inflammation, wherever it starts, appears to be a common thread running through many age-related conditions, and cleaner air appears to help keep that inflammation in check.

You cannot control the air quality of an entire city, but there are a few sensible steps that may help lower your everyday exposure. On days when local air quality is reported as poor, especially during wildfire smoke or heavy traffic pollution, consider limiting time outdoors and keeping windows closed. Indoor air filters can help reduce particle levels inside the home. Supporting overall gut health through a diet rich in fiber, vegetables, and fermented foods may also help maintain the kind of healthy bacterial balance that researchers believe protects against inflammation. As with any health concern, if you have questions about your own risk factors for Parkinson’s disease, your doctor is the best person to talk to.

Source material for this news draws on a recent scientific review discussing air pollution and Parkinson’s disease pathology, published via Fight Aging!