Ambient air pollution and multiple sclerosis: a systematic review

Area of Science:

• Environmental Health Sciences
• Neuroepidemiology
• Toxicology

Background:

• Environmental risk factors are increasingly implicated in the development and progression of neurological diseases.
• Previous studies suggest a potential association between air pollution exposure and multiple sclerosis (MS) incidence or recurrence.

Purpose of the Study:

• To systematically review and synthesize existing evidence on the relationship between ambient air pollution and multiple sclerosis.
• To investigate specific air pollutants as potential environmental triggers or exacerbating factors for MS.

Main Methods:

• A comprehensive systematic literature search was performed across major scientific databases (PubMed, Scopus, Science Direct, Embase, Web of Science) until January 2020.
• Search terms included specific air pollutants (CO, PM2.5, PM10, SO2, NO2) and 'Multiple sclerosis'.
• Seventeen studies met the inclusion criteria; however, heterogeneity in methodologies and outcomes precluded a meta-analysis.

Main Results:

• Eight studies found a significant association between exposure to particulate matter (PM) and the prevalence or relapse of MS.
• Three studies indicated a link between nitrogen dioxide (NO2) and nitrogen oxides (NOx) and MS recurrence or prevalence.
• Conversely, three cohort studies reported no significant association between air pollution and MS occurrence or recurrence.

Conclusions:

• The current systematic review suggests a potential link between exposure to outdoor air pollution, specifically particulate matter and nitrogen oxides, and the prevalence or relapse of multiple sclerosis.
• While some studies indicate a relationship, the heterogeneity of findings highlights the need for further investigation to establish definitive causal links and understand the underlying mechanisms.