Long-term air pollution exposure shows no clear link to ALS in UK study
Findings of large analysis 'do not support a measurable effect' on disease risk
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- A large U.K. study found no clear link between long-term air pollution exposure and ALS risk.
- The researchers analyzed particulate matter and nitrogen oxides in more than 500,000 people over nearly a decade.
- Further study is needed to explore other environmental factors for ALS risk, the team noted.
Long-term exposure to air pollution is not associated with an altered, or increased, risk of amyotrophic lateral sclerosis (ALS).
That’s according to a new study from the U.K. that used data from more than 500,000 people in the European nation who were followed, on average, for nearly a decade. Fewer than 1,000 individuals developed ALS, the analysis determined.
“Our findings do not support a measurable effect of air pollution exposure on ALS risk in this large population-based setting,” the researchers wrote, noting that “several sensitivity analyses were conducted to assess the robustness of the results.”
The study, titled “Long-Term Exposure to Ambient Air Pollution and Incident Amyotrophic Lateral Sclerosis A Prospective Cohort Analysis of the UK Biobank,” was published in the journal Neurology by a research team from the University of Oxford.
ALS is a neurodegenerative disorder in which motor neurons, the nerve cells that control movement, become progressively damaged and die.
The causes of ALS remain incompletely understood: Genetic mutations are known to underlie some cases, but other factors including environmental exposures have also been shown to influence ALS risk.
Most earlier studies measured air pollution at single time point
Air pollution has been linked to an increased risk of many health problems, such as certain lung diseases and dementia.
While some previous studies have suggested that people who are exposed to greater amounts of air pollution are more likely to develop ALS, others have challenged those results. A notable limitation of these previous studies, according to researchers, is that often air pollution is measured at a single point in time, rather than being tracked over the course of years.
“Evidence regarding the association between air pollution and ALS remains limited and inconsistent,” the scientists wrote, noting a lack of analysis regarding long-term exposure.
Aiming to get more clarity on the association between air pollution and ALS, this research team conducted an analysis using data from the U.K. Biobank, a large study tracking health outcomes for people living in the U.K.
The analysis covered data from 501,308 people, ages 40-69. Over a median follow-up time of 8.4 years, 687 of them (about 0.1%) developed ALS.
Using statistical analyses, the researchers looked for associations between ALS risk and long-term exposure to two main types of pollutants: particulate matter, which is primarily dust and other small particles in the air, and nitrogen oxides, basically pollutants that are produced from the burning of fossil fuels. Pollutants due to fossil fuels contribute to environmental issues like smog and acid rain.
“We focused on particulate matter and nitrogen oxides, which are established indicators of ambient air pollution,” the researchers wrote. The team noted that particulate matter “arises from both primary sources, such as vehicle exhaust, industrial emissions, and biomass burning, and from secondary formation [that is, chemical reactions high in the atmosphere].”
Nitrogen oxides, meanwhile, are “primarily emitted from traffic and fossil fuel combustion, [and] are widely used markers of urban air pollution,” the researchers wrote.
New analysis looked at each person’s residential address history
Exposure to these pollutants was estimated based on data from the U.K. Department for Environment, Food and Rural Affairs, which compiles annual average concentrations of multiple air pollutants in each square kilometer. This was linked to data from each person’s residential address histories.
Across the analyses, the statistical models consistently showed no significant relationship between exposure to any of the tested pollutants and ALS risk, the researchers noted.
With sufficient statistical power to detect even modest [statistically significant associations], we found no evidence of an association between long-term exposure to ambient air pollutants.
According to the scientists, their sample size was large enough that, if statistically meaningful associations did exist, they should have been able to detect them.
“With sufficient statistical power to detect even modest [statistically significant associations], we found no evidence of an association between long-term exposure to ambient air pollutants,” the scientists concluded.
This negative finding highlights “the need to investigate alternative potential environmental contributors” to ALS risk, the team noted.
While the size of the U.K. Biobank allowed the scientists to conduct statistically robust analyses, the team noted that this data source is not without limitations. Specifically, individuals in this study tend to be more commonly white people, and those who were better educated and wealthier than the general population in the U.K. Per the team, those demographics “may affect exposure to air pollution and generability to populations with different ancestral, sociodemographic, or health profiles.”
The team also said that their study does not address whether other forms of air pollution besides particulate matter and nitrogen oxides may affect ALS risk.
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