LOS ANGELES—People with consistently high occupational exposures to diesel exhaust may have a higher risk of amyotrophic lateral sclerosis (ALS), and that risk may increase with greater exposure, according to a preliminary study presented at the American Academy of Neurology’s 70th Annual Meeting.
“There is some suggestion from previous studies of occupation that workers in jobs with higher exposure to diesel exhaust may have a higher risk of ALS. However, no studies have directly looked at the relationship between diesel exhaust exposure during different time points in life and ALS,” said lead study author Aisha Dickerson, PhD, a postdoctoral fellow in the Departments of Environmental Health and Epidemiology at the Harvard T.H. Chan School of Public Health in Boston. “The overall risk of developing ALS is low, but our findings suggest that the greater the exposure to diesel exhaust, the greater the risk of developing ALS.”
Aisha Dickerson, PhD
For this study, researchers identified 1,639 people with an average age of 56 from the Danish National Patient Registry who were diagnosed with ALS between 1982 and 2013. For each case, 100 birth year- and sex-matched controls were selected using the Danish Central Person Registry. Employment history since 1964 was acquired from the nationwide Danish Pension Fund.
Cumulative diesel exhaust exposures prior to index dates (the date of ALS diagnosis in the ALS case) were estimated using a job exposure matrix. The estimated exposure was based on potential hazards for specific jobs, including service station attendants, bus drivers, and construction workers. Cumulative exposure was calculated for up to five and 10 years before the diagnosis time period, allowing for the time it may take diesel exhaust to have an effect on the body. Subjects who were older than age 25 in 1964 were excluded to diminish exposure misclassification.
The participants were divided into quartiles based on the amount of exposure to diesel exhaust. Men with any exposure to diesel exhaust at jobs held at least 10 years prior to their date of inclusion in the study were 20% more likely to have ALS than men with no exposure to exhaust during the same time period. For men who had a greater than 50% likelihood of being exposed to exhaust based on their occupation, the link was stronger. That group was 45% more likely to develop ALS than those with no exhaust exposure at both five and 10 years prior to study inclusion. No associations were observed among women, although the types of jobs and even tasks performed in the same job can differ substantially for men and women.
The results were adjusted for other factors that could affect risk of ALS including socioeconomic status and the region of Denmark where a participant lived.
“This type of exposure deserves more attention and study as we work to develop a better understanding of what causes ALS,” Dr. Dickerson said. “Importantly, the general population can be exposed to diesel exhaust from traffic pollution. Understanding whether that exposure increases ALS risk is also an important question to pursue.”
This study does not show that diesel exhaust causes ALS; it only shows an association, the researchers said. One study limitation was that investigators used a job exposure matrix to estimate occupational diesel exhaust levels and could not directly measure personal exposures. However, any potential misclassification caused by this would likely have diminished the observed associations, the researchers noted.
The study was supported by the National Institute of Environmental Health Sciences and the National Institutes of Health.