The air we breathe every day may have a greater effect on our brains than many people realize.
A new study published in Environment International suggests that people who spend many years breathing polluted air may face a higher chance of developing Parkinson’s disease.
Researchers from the University of Cambridge reached this conclusion after carefully reviewing and combining evidence from previous scientific studies.
Air pollution is already known to increase the risk of heart disease, stroke, lung disease, and dementia. Scientists are now asking whether it may also contribute to diseases that slowly damage the nervous system. Parkinson’s disease is one of the most common of these conditions.
It develops when nerve cells that produce dopamine gradually disappear, making it harder for the brain to control movement. Symptoms usually include shaking, slow movement, muscle stiffness, poor balance, and later, problems with sleep, mood, and thinking.
Because Parkinson’s develops slowly over many years, researchers believe that long-term environmental exposures may contribute alongside inherited genes. Air pollution has become an important area of investigation because billions of people around the world are exposed to it every day.
To investigate, the Cambridge researchers carried out a systematic review and meta-analysis, a research method that pools results from many previous studies.
By combining information from different populations, scientists can produce more reliable estimates than any single study alone. The review included 26 studies examining Parkinson’s disease together with several smaller studies of multiple sclerosis and motor neurone disease.
The analysis found the clearest evidence for two pollutants called PM2.5 and PM10. These are tiny particles released from traffic, factories, power plants, construction work, wood burning, road dust, tyre wear, and other sources.
Because they are so small, they can be inhaled deep into the lungs. Some evidence suggests the smallest particles may even enter the bloodstream and eventually affect the brain.
According to the review, higher long-term exposure to PM2.5 was linked with a 10% increase in the relative risk of Parkinson’s disease for every 5 micrograms per cubic metre increase.
Higher exposure to PM10 was linked with an 18% increase in relative risk for every 15 micrograms per cubic metre increase. Although the researchers also examined other pollutants, there was not enough consistent evidence to draw firm conclusions.
Scientists think these particles may promote inflammation and oxidative stress throughout the body. Over many years, these processes may damage sensitive brain cells and encourage abnormal protein build-up associated with Parkinson’s disease.
The review did not find convincing evidence that air pollution increases the risk of multiple sclerosis or motor neurone disease, but only a few studies were available. More research involving larger populations is needed before these questions can be answered.
Importantly, this study cannot prove that air pollution directly causes Parkinson’s disease. Observational studies can only identify relationships, not direct cause and effect. However, when many studies point in the same direction, confidence in the overall finding becomes stronger.
The researchers say the results strengthen the case for cleaner air. They have also developed an online evidence tool that allows decision-makers to compare strategies such as congestion charging, better public transport, active travel, electric vehicles, and low-emission zones to reduce pollution and improve public health.
Overall, this review provides important evidence that protecting air quality may also help protect brain health. Its strengths include a comprehensive analysis of many studies, while its limitations include differences in study design and limited evidence for some pollutants.
Even with these limitations, the findings support stronger public health policies aimed at reducing air pollution for current and future generations.
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 information about brain health, please see recent studies that blueberry supplements may prevent cognitive decline, and results showing Plant-based diets could protect cognitive health from air pollution.
Source: University of Cambridge.
