Particulate matter air pollution and risk of Multiple Sclerosis in a large study of female nurses.

Abstract

Background: Multiple Sclerosis (MS) is a common autoimmune disorder of the nervous system of unknown origin. The incidence of MS is increasing throughout the world, but the specific reason for this increase has not been identified. Cigarette smoking, whose effects on the immune and nervous system are thought to be similar to air pollution, has consistently been associated with increased MS risk, as well as worse progression of MS. Aims: In this study, we used data from a large prospective study on US women to examine whether there is an association between particulate matter (PM) air pollution and risk of MS. Methods: This study included participants from an ongoing prospective cohort study, the Nurses’ Health Study II (NHS II). Cumulative average exposure to different size fractions of PM up to the time of MS onset, was estimated using a spatio-temporal model by linking each individual’s places of residence throughout the study with location-specific air pollution levels. We used multivariable Cox proportional hazards models to estimate the risk of MS associated with PM10, PM2.5 and PM10-2.5, adjusting for smoking, body mass index at age 18, ethnicity, population density, region, season, birth tier, income and housing value. Results: Overall, we found no significant associations between PM2.5, PM10-2.5, or PM10 exposure and MS risk. The RR comparing the top quintile to the bottom quintile of exposure was 1.30 (95% CI: 0.84, 2.01), 0.94 (95% CI: 0.65, 1.37) and 1.13 (95% CI: 0.76, 1.65) for PM10, PM2.5 and PM10-25, respectively. In sensitivity analyses among never smokers, we did not find significant associations for any of the exposures of interest. Conclusions: In this study, we did not find convincing evidence that exposure to air pollution during adulthood is a risk factor for MS.