20 January 2026

Prolonged exposure to air pollution may be linked to an increased risk of serious neurodegenerative diseases such as ALS, and appears to accelerate the disease process, according to researchers at the Karolinska Institute in Sweden. The study is published in the journal JAMA Neurology.

“There is a clear correlation, despite the fact that air pollution levels in Sweden are lower than in many other countries,” explains Jing Wu, a researcher at the Karolinska Institute’s Institute of Environmental Medicine. “This underlines the importance of improving air quality.

Motor neurone disease (MMN) is a serious neurological disorder in which the nerve cells that control voluntary movement deteriorate so much that they cease to function, leading to muscle atrophy and paralysis. Amyotrophic lateral sclerosis (ALS) is the most common form, accounting for around 85-90% of cases.

Environmental factors may play a role

The causes of these diseases remain largely unknown, but environmental factors have long been suspected of contributing to them. The new study shows that air pollution could be one of these factors.

The study involved 1,463 participants in Sweden with newly diagnosed ALS, compared with 1,768 siblings and more than 7,000 matched controls from the general population. The researchers analysed levels of particulate matter ( _PM2.5 , _PM2.5-10 , PM ₁₀ ) and nitrogen dioxide in their homes up to ten years before their diagnosis.

The average annual values for these pollutants were slightly higher than WHO recommendations, and the maximum values were well below those observed in countries with high levels of air pollution.

Risk increased by up to 30

Prolonged exposure to air pollution, even at relatively low levels as in Sweden, was associated with a 20-30% increased risk of developing ALS. What’s more, people who had lived in more polluted areas showed more rapid motor and pulmonary deterioration after diagnosis. They also had a higher risk of death and were more likely to require mechanical ventilation.

“Our results suggest that air pollution may not only contribute to the onset of the disease, but also influence the rate at which it progresses,” says Caroline Ingre, Assistant Professor in the Department of Clinical Neurosciences at the Karolinska Institute.

Limiting their analyses to ALS patients, the researchers found a pattern virtually identical to that observed for the ALS group as a whole.

Inflammation and oxidative stress

The researchers stress that the study does not elucidate the mechanisms underlying this association, but previous research indicates that air pollution can cause inflammation and oxidative stress in the nervous system. As this is an observational study, no causal link can be established.

This study is based on Swedish registry data and was funded by several organisations, including the US Centers for Disease Control and Prevention (CDC), the Swedish Research Council and the Karolinska Institute . Some authors have received research grants and/or honoraria from pharmaceutical companies; the full conflict of interest declaration is available in the article.

Translation: Eric Kisbulck

Source: Karolinska Institut