Long-term air pollution and risk of amyotrophic lateral sclerosis mortality in the Women's Health Initiative cohort.
BACKGROUND
Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder with no cure. Although the etiology of sporadic ALS is largely unknown, environmental exposures may affect ALS risk.


OBJECTIVE
We investigated relationships between exposure to long-term ambient particulate matter (PM) and gaseous air pollution (AP) and ALS mortality.


METHODS
Within the Women's Health Initiative (WHI) cohort of 161,808 postmenopausal women aged 50-79 years at baseline (1993-1998), we performed a nested case-control study of 256 ALS deaths and 2486 matched controls with emphasis on PM constituents (PM2.5, PM10, and coarse PM [PM10-2.5]) and gaseous pollutants (NOx, NO2, SO2, and ozone). Time-varying AP exposures estimates were averaged 5, 7.5, and 10 years prior to ALS death using both a GIS-based spatiotemporal generalized additive mixed model and ordinary kriging (empirical and multiple imputation, MI). Conditional logistic regression was used to estimate the relative risk of ALS death.


RESULTS
In general, PM2.5 and PM10-related risks were not significantly elevated using either method. However, for PM10-2.5, odds ratios (ORs) were >1.0 for both methods at all time periods using MI and empirical data for PM10-2.5 (coarse) except for 5 and 7.5 years using the kriging method with covariate adjustment.


CONCLUSION
This investigation adds to the body of information on long-term ambient AP exposure and ALS mortality. Specifically, the 2019 US Environmental Protection Agency (EPA) Integrated Science Assessment summarized the neurotoxic effects of PM2.5, PM10, and PM10-2.5. The conclusion was that evidence of an effect of coarse PM is suggestive but the data is presently not sufficient to infer a causal relationship. Further research on AP and ALS is warranted. As time from symptom onset to death in ALS is ∼2-4 years, earlier AP measures may also be of interest to ALS development. This is the first study of ALS and AP in postmenopausal women controlling for individual-level confounders.