Predisease pollution exposure may worsen survival in ALS, study says

People with amyotrophic lateral sclerosis (ALS) who are exposed to high levels of certain pollutants in the years before disease onset have worse survival outcomes, a new study shows.

The findings add to building evidence that pollution and environmental toxins can affect the course of ALS. Researchers are calling for continued efforts to limit exposure to compounds that may accelerate ALS, particularly chemicals called chlordane compounds and hexachlorobenzene (HCB).

“Ongoing exposure to these compounds persists, and there is no reason to expect that, even at lower levels, differences in exposure would not remain associated with differences in survival,” researchers wrote. “This finding underscores the potential importance of exposure reduction — including for compounds with modes of action similar to HCB and chlordane.”

The study, “Associations between Pre-Disease Biomarkers of Persistent Organic Pollutants and Amyotrophic Lateral Sclerosis Survival in the Danish Diet, Cancer and Health Study Cohort,” was published in the Annals of Neurology.

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ALS is a progressive disease that causes muscle weakness and eventual paralysis. ALS is almost always fatal within a few years, but there’s a lot of unexplained variability in survival time after disease onset.

An emerging body of evidence has hinted that ALS survival may be influenced by exposure to toxins or pollutants in the environment. Specifically, a handful of prior studies have found that ALS survival tends to be worse in patients who have higher levels of persistent organic pollutants (POPs) in their blood.

“POPs are toxic, long-lasting organic chemicals that resist degradation, disperse widely through air, water, and soil, and accumulate in living organisms, with increasing concentrations at higher levels of the food chain,” the researchers wrote.

Prior research linking POPs with ALS survival has relied on blood samples that were collected after ALS onset — making it impossible to know if POP levels were influencing ALS, or if the disease itself was changing levels of POPs in the body. To address this gap, researchers analyzed data from a study that was conducted in Denmark in the 1990s.

Our findings provide prospective evidence that pre-disease exposure to certain POPs, particularly HCB and chlordane compounds, may adversely affect ALS survival.

Using national databases, the researchers identified 166 people who had participated in this study and later developed ALS. The researchers measured POP levels in blood samples collected during the original study, years before ALS onset.

“The strengths of our study include its prospective design, which relied on pre-disease blood samples collected several years before ALS diagnosis,” the researchers wrote.

Roughly two dozen specific types of POPs were evaluated. In statistical analyses, higher levels of all but two of these molecules were associated with shorter ALS survival times, though many of the associations were not statistically significant (meaning there’s a nonnegligible likelihood that the differences are due to random chance).

Two types of POPs — chlordane compounds and HCB — showed statistically significant associations with survival in the researchers’ analyses. The scientists noted that both chemicals have been shown to be toxic to nerve cells in lab models, though their effects on human health are poorly understood.

“Our findings provide prospective evidence that pre-disease exposure to certain POPs, particularly HCB and chlordane compounds, may adversely affect ALS survival,” the researchers concluded.

The researchers called for further studies into how these chemicals may affect ALS. They also emphasized a need for regulatory efforts to limit exposure to pollution and toxins.