Researchers have provided more evidence that exposure to toxic environmental pollutants raises the risk for amyotrophic lateral sclerosis (ALS).
Unlike previous research, the new study used both surveys and measurement of toxic chemicals in blood.
"This is not going to alter treatment at this point, but it really helps us think about the types of things we can do to prevent ongoing leakage of chemicals, and limit the pollution that we put into the environment, because it does have an impact, we believe, on disease," study author Stephen A. Goutman, MD, assistant professor and director, ALS Clinic, University of Michigan, Ann Arbor, told Medscape Medical News.
The study was published online May 6 in JAMA Neurology.
From a tertiary center in Michigan, researchers identified 156 patients with ALS and recruited 128 controls with no ALS or family history of any neurodegenerative disorder.
They determined likely exposures through self-administered questionnaires on occupational and residential history, and military service, and collected other information on smoking history and demographic characteristics.
From blood samples, they examined concentrations of 122 environmental organic pollutants, including organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), which were chemicals used as coolants or lubricants in electrical equipment, and brominated flame retardants (BFRs).
Investigators accounted for confounding variables, including tobacco use, age, sex, education level, marital status, ethnicity, and military service.
The analyses showed a consistent association between occupational pesticide exposure and ALS. For any past exposure, the odds ratio (OR) was 5.09 (95% confidence interval [CI], 1.85 - 13.99; P < .01).
Ever having worked for the US Armed Forces was also associated with increased ALS risk (OR, 2.31; 95% CI, 1.02 - 5.25; P < .05).
The link between being in the armed forces and ALS isn't new, said Dr Goutman. Theories possibly explaining the association include increased exposure to chemicals used during conflicts (especially during the first Gulf war), increased physical activity, multiple vaccinations, and traumatic injury.
Unexpectedly, occupational exposure to lead showed a statistically significant protective effect for ALS (OR, 0.32; 95% CI, 0.13 - 0.81; P < .05).
Dr Goutman said this requires additional follow-up but pointed out that lead was not measured in blood and that the protective effect was seen only when the authors looked at occupational exposure recalled over a lifetime, not at individual exposure time windows of susceptibility.