Long-term exposure to air pollution increases the risk of a person developing amyotrophic lateral sclerosis, a Dutch study shows.
The study, “Long-Term Air Pollution Exposure and Amyotrophic Lateral Sclerosis in Netherlands: A Population-based Case–control Study,” appeared in the journal Environmental Health Perspectives.
Scientists say it’s likely that 90 to 95 percent of ALS cases stem from the interaction of genetic and environmental factors. Smoking is a well-known risk factor for ALS. But there has been a shortage of information on other factors that may help trigger the disease.
Researchers have linked long-term exposure to air pollution to cardiovascular and respiratory diseases. More recently, they have linked the pollution to neurodegenerative diseases such as Parkinson’s and Alzheimer’s. But little information has been available about pollution’s association with ALS.
Based on toxicological and animal studies, researchers have hypothesized that very small airborne particles may cross or disrupt the blood-brain barrier. This may cause chronic brain inflammation, oxidative stress, and abnormalities in the brain’s white matter, collectively contributing to ALS, they have speculated. Oxidative stress is an imbalance between the body’s production of free radicals, which can damage tissue, and its ability to counteract their harmful effects.
Scientists have found higher concentrations of fine air particles in the brains of people living in big population centers than in those living in less polluted areas.
The Dutch researchers decided to see if there were a link between long-term exposure to air pollution and people’s susceptibility to ALS.
Leaders of the research effort were Leonard H. van den Berg, a full professor of Neurology & Neurosurgery at the University Medical Center Utrecht, and Roel C.H. Vermeulen, an associate professor of Molecular Epidemiology and Risk Assessment at Utrech University’s Institute for Risk Assessment Sciences.
The team did a seven-year population-based study from January 2006 to January 2013 that involved 917 ALS patients and 2,662 controls. They used models from the European Study of Cohorts for Air Pollution Effects (ESCAPE) project to determine annual mean air pollution levels, starting in 1992.
They discovered that people exposed to the highest levels of nitrogen oxides and to fine particles in the air were at significantly higher risk of developing ALS than others. Fine particles are more likely to penetrate into the lungs and other organs.
All these air pollutants are traffic-related and therefore more concentrated in urban areas.
The nitrogen oxide and fine particulate results remained significant even after researchers accounted for the degree of urbanization where patients lived.
Researchers said the results gibed with previous studies showing that being exposed to hazardous air aromatic solvents increases the risk of someone developing ALS. They also found an elevated risk of ALS among truck and bus drivers, and machine workers and operators, underscoring a reported association between ALS and diesel exhaust.
Overall, the Dutch study provided “evidence for the association between long-term exposure to traffic-related air pollution and increased susceptibility to ALS,” the researchers wrote. “Our findings further support the necessity for regulatory public health interventions to combat air pollution levels and provide additional insight into the potential pathophysiology of ALS.”
Future studies should aim to replicate these findings in other populations, the team said.
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