Jin Wu, a researcher at the Institute of Environmental Medicine, emphasizes that although pollution levels in Sweden are lower than in several other countries, the link between air pollution and neurological diseases remains evident. "This underscores the importance of improving air quality," he noted.
Neurodegenerative diseases, such as ALS, lead to the degradation of nerve cells that control voluntary movements, which in turn causes muscle atrophy and paralysis. ALS is the most common among them, accounting for 85-90% of all cases.
Environmental Aspects
Although the exact causes of these diseases remain unclear, many studies suggest that environmental factors play a significant role. This study found that polluted air could be one of those factors.
The study involved 1,463 Swedes with recently diagnosed motor neuron diseases, who were compared with 1,768 of their siblings, as well as more than 7,000 control participants from the general population. Researchers analyzed levels of pollutants (PM2.5, PM2.5–10, PM10) and nitrogen dioxide based on the participants' addresses over the ten years prior to diagnosis.
The average annual concentrations of these pollutants slightly exceeded the recommendations of the World Health Organization, while peak values were significantly lower than in countries with high levels of air pollution.
Increased Risk by Up to 30%
Prolonged exposure to polluted air, even at relatively low levels typical for Sweden, was associated with a 20-30% increased likelihood of developing motor neuron diseases. Moreover, patients living in areas with high pollution levels experienced more rapid deterioration of motor and pulmonary functions after diagnosis. They also had an increased risk of mortality and a greater need for invasive ventilation methods.
"Our data suggest that air pollution may not only contribute to the onset of diseases but also affect the rate of their progression," comments Caroline Ingre, an adjunct professor at the Department of Clinical Neurology at the Karolinska Institute.
When analyzing only patients with ALS, researchers found a similar pattern to that observed for the entire group of motor neuron diseases.
Inflammatory Processes and Oxidative Stress
Although the study cannot establish the causes of this connection, scientists note that previous work shows that air pollution can provoke inflammatory responses and oxidative stress in the nervous system. Since this is an observational study, the causal relationship remains unclear.
The research relied on data from Swedish registries and was supported by several organizations, including the Centers for Disease Control and Prevention (CDC), the Swedish Research Council, and the Karolinska Institute.
