Airborne Pollution: A Potential Risk Factor for Multiple Sclerosis in Colder Climates.

Multiple Sclerosis (MS), a neurodegenerative disease of unknown etiology, which affects approximately 450 of every 100 000 women in the USA. Using an ecological observational study design and publicly available data from the Center for Disease Control and Prevention in the USA, we assessed trends in county-level, age-adjusted female MS mortality rates between 1999 and 2006 to determine if they were correlated with environmental factors, including the county's PM2.5. In counties with colder winters, there was a significant positive association between the average PM2.5 index and the MS mortality rate, after controlling for the county's UV index and median household income. This relationship was not apparent in counties with warmer winters. We also found that colder counties had higher MS mortality rates, even after controlling for the UV and PM2.5 indices. The findings from this study provide county-level evidence for a temperature-dependent association between PM2.5 pollution and MS mortality rates, which should be further investigated.