Healthcare (Commonwealth Union) – The detrimental effects of air pollution on health has been a key focus among a wide variety of researchers. However, determining what level of pollution and what specific components are responsible for many multiple diseases has been a key challenge.
A research team from the University of Cambridge has noted that prolonged exposure to certain forms of air pollution may be associated with a higher risk of Parkinson’s disease, following a comprehensive review of existing scientific evidence.
Air pollution continues to be a leading public health problem globally, and long-term exposure to fine particulate matter has already been associated with an increased risk for several conditions, such as stroke and dementia. Possible links between air pollution and neurodegenerative diseases such as Parkinson’s disease, multiple sclerosis and motor neurone disease have also been suggested by researchers. But past studies have often been hobbled by small sample sizes, inconsistent findings or inconclusive results.
To better understand these associations, scientists from IMS Epidemiology at the University of Cambridge undertook a systematic review and meta-analysis of published research in a study published in Environment International. Pooling data across studies was a way to create a stronger evidence base and to find clearer patterns in spite of variation across individual studies.
The review looked at 26 studies of Parkinson’s disease, three studies of multiple sclerosis and three studies of motor neurone disease.
Researchers have found two types of air pollutants that are linked to a higher risk of developing Parkinson’s disease, a neurological disorder affecting some 6 million people worldwide:
Fine particulate matter (PM2.5): These are very small particles suspended in the air that are 2.5 microns or less in diameter, and can penetrate deep into the lungs when inhaled. PM2.5 pollution has many different sources, including emissions from traffic (vehicle exhaust and other emissions), power generation, industrial activity, wood burning stoves and fireplaces, and dust from construction. They can also be formed in the atmosphere by chemical reactions between pollutants such as sulphur dioxide and nitrogen oxides. PM2.5 particles are so small that they can stay in the air for a long time and can travel long distances away from their original sources.
Coarse particulate matter (PM10): These particles are larger than PM2.5 but are still small enough to enter the respiratory system. PM10 pollution comes from sources such as road and construction dust, pollen, mould spores, vehicle emissions—particularly from diesel engines—as well as non-exhaust traffic pollution caused by brake and tyre wear, and emissions from industrial activities.
The researchers estimated that exposure to an additional 5 micrograms per cubic metre (μg/m³) of PM2.5 was associated with a 10% increase in the relative risk of Parkinson’s disease. For comparison, the average roadside PM2.5 level recorded in Central London during 2023 was 10 μg/m³.
Similarly, every 15 μg/m³ increase in PM10 exposure was associated with an 18% rise in the relative risk of Parkinson’s disease. The average roadside PM10 concentration in Central London in 2023 was measured at 17 μg/m³.
Researchers said future investigations should examine these pollutants further, including how combinations of different pollutants may interact, as more evidence emerges.
The study also found no clear connection between air pollution exposure and either multiple sclerosis or motor neurone disease. However, the researchers noted that the lack of evidence may be due to the small number of studies conducted in these areas.
“There are still relatively few robust studies that explore the link between air pollution and Parkinson’s disease, but even so, it’s becoming clear that there is a link. We found evidence of a link with two types of pollutants in particular, but even though the evidence was inconclusive for other types, this may be down to how the studies were designed. We urgently need more research, in larger populations, to examine what is a significant public health issue,” explained Dr Annalan Navaratnam, and Clinical Research Fellow at IMS Epidemiology, University of Cambridge.
