Long-term air pollution may raise the risk of motor neurone disease and worsen outcomes after diagnosis, new research suggests.
The study, one of the largest to examine this link, tracked 1,463 people newly diagnosed with MND in Sweden, comparing them with over 7,300 population controls and nearly 1,800 sibling controls to account for genetic and shared environmental factors.
Using high-resolution spatiotemporal models, researchers examined detailed residential exposure to multiple air pollutants over periods of up to 10 years before diagnosis.
The analysis found a consistently higher risk of MND among people exposed to elevated levels of fine particulate matter, coarse particulate matter and nitrogen dioxide.
Dr Jing Wu, lead author, said: “Our results suggest that air pollution, even at the relatively low levels typical of Sweden, may play a role in both the development and the progression of this devastating disease.”
The strongest associations were seen with longer-term exposure, particularly over a 10-year period, suggesting cumulative effects of poor air quality.
Particulate matter refers to tiny particles suspended in the air, often from traffic, industry or other sources.
The study also found that people with MND who had higher long-term exposure before diagnosis experienced worse clinical outcomes, including an increased risk of death and a greater likelihood of requiring invasive ventilation.
Patients exposed to higher levels of particulate matter showed a faster decline in motor and respiratory function after diagnosis, although no clear association was seen with bulbar function, which affects speech and swallowing.
The researchers, drawn from medical and academic institutions in Sweden, say their findings help clarify previously mixed evidence on the relationship between air pollution and MND.
The authors note that the biological mechanisms are not yet fully understood, but suggest air pollution may interact with known genetic risk factors through pathways linked to oxidative stress and neuroinflammation, which refers to cellular damage and inflammation in the nervous system.
Commenting on the research, Dr Brian Dickie, chief scientist at the MND Association, said: “This is a well performed study indicating an association between long-term exposure to higher air pollution levels and a small, but notable, increased risk of developing MND, as well as faster disease progression, although these observations were not consistent across all subtypes of MND.”
“It is important to stress that ‘correlation’ does not mean ‘causation’ – and indeed, findings from previous research on the effects of air pollution have been inconsistent.
“The researchers are therefore cautious with their interpretation of the results, acknowledging that potential confounding factors, together with a lack of some additional data, prevent strong conclusions being made.
“For example, key information on the delay between symptom onset and diagnosis, which is known to be strongly linked to rate of disease progression, was not available.
“We know that the vast majority of cases of MND are likely to occur through a combination of potentially many genetic, environmental and lifestyle factors.
“Scandinavian countries are known to have particularly high proportion of some genetic risk factors for MND within the population but, unfortunately, genetic data was not available for this study.
“These results point to the importance of integrating genetic information into future epidemiology studies, if we are to make genuine and significant inroads in understanding the causes of MND.”
