Long-term exposure to polluted air may increase the risk of developing Parkinson’s disease, according to a major review of previous research published in Environment International.
The study was led by researchers at the University of Cambridge, who combined the results of many earlier studies to better understand whether breathing polluted air affects brain health. Their findings add to growing evidence that air pollution harms far more than the lungs and heart. It may also increase the risk of diseases that damage the brain.
Parkinson’s disease is a progressive brain disorder that affects movement. People may first notice shaking, stiffness, slower movement, balance problems, or changes in speech.
As the disease progresses, many also develop sleep problems, depression, constipation, and memory difficulties. Around six million people worldwide are living with Parkinson’s disease, and the number continues to rise as populations age.
Scientists believe Parkinson’s develops because certain brain cells that produce dopamine gradually die. Dopamine is a chemical messenger that helps control smooth and coordinated movement. Researchers have long known that age and genetics play a role, but environmental factors are also thought to contribute. Air pollution has become one of the leading suspects.
Instead of carrying out a new experiment, the Cambridge team performed a systematic review and meta-analysis. This method combines many high-quality studies into one larger analysis, helping researchers identify patterns that smaller individual studies may miss.
The review included 26 studies on Parkinson’s disease and a small number of studies on multiple sclerosis and motor neurone disease.
The strongest evidence involved two types of tiny particles known as PM2.5 and PM10. PM2.5 particles are extremely small and can travel deep into the lungs before entering the bloodstream.
They come from vehicle exhaust, power stations, factories, wood burning, and chemical reactions in the atmosphere. PM10 particles are slightly larger but are still small enough to be inhaled. They come from road dust, construction work, pollen, brake and tyre wear, and industrial pollution.
The researchers estimated that every increase of 5 micrograms per cubic metre of PM2.5 was linked with a 10% higher relative risk of Parkinson’s disease. Every increase of 15 micrograms per cubic metre of PM10 was linked with an 18% higher relative risk.
The study did not find clear evidence for other pollutants such as nitrogen dioxide, ozone, carbon monoxide, sulfur dioxide, or soot, mainly because there were too few consistent studies.
The researchers believe polluted air may trigger long-term inflammation and oxidative stress inside the body. These processes may damage brain cells and encourage the build-up of the protein alpha-synuclein, one of the hallmarks of Parkinson’s disease. People who are genetically more vulnerable may be especially affected.
The study also looked for links with multiple sclerosis and motor neurone disease but found no clear evidence. However, the authors caution that very few studies have been carried out, so stronger conclusions cannot yet be made.
The findings do not prove that air pollution directly causes Parkinson’s disease. They show an association, meaning other factors may also contribute. Even so, the large review strengthens concerns that cleaner air could help reduce the future burden of neurological disease.
The researchers also highlighted an open-access tool developed at the University of Cambridge that helps governments compare policies such as low-emission zones, cleaner public transport, electric vehicles, and better city planning to reduce traffic-related air pollution.
Overall, this review is one of the strongest summaries of current evidence. Its main strength is combining many studies, but differences between the original studies mean more high-quality research is still needed. Even so, the findings support continued efforts to improve air quality because cleaner air is likely to benefit many parts of human health, including the brain.
If you care about Parkinson’s disease, please read studies that Vitamin B may slow down cognitive decline, and Mediterranean diet could help lower risk of Parkinson’s.
For more health information, please see recent studies about how wheat gluten might be influencing our brain health, and Olive oil: a daily dose for better brain health..
Source: University of Cambridge.
