Air pollution and MS risk

Air pollution may be another environmental risk factor for developing multiple sclerosis (MS), new research suggests.

A large cohort study of almost 550,000 individuals living in Italy showed that participants living in areas with high levels of pollutants had a significantly greater risk of developing MS than those who lived in areas with low levels of pollutants.

The findings further confirm a relationship between exposure to air pollutants and risk for MS that has been shown in previous research.

Several environmental factors may trigger an abnormal immune response that manifests in MS. The most studied of these are low vitamin D level, cigarette smoking, and an unhealthy diet.

However, other environmental factors deserve to be studied ― pollution included.

Among the most toxic air pollutants are particulate matter (PM), which is a mixture of fine solid and liquid particles suspended in the earth's atmosphere. PM may range from 2.5 microns (PM2.5) to 10 microns (PM10) in diameter.

The main sources of such pollutants are household and commercial heating (53%) and industrial activities (17%), followed by road vehicle and non-road vehicle use, agriculture, and electricity production.

Epidemiologic research has uncovered a relationship between air pollution and MS. A large American study published in 2008 in Science of the Total Environment showed a significant association between MS prevalence and PM10 levels (P < .001).

Other studies have shown an increase in the number of clinical relapses of MS that were linked to air pollution.

The current investigators assessed the association between PM2.5 levels and MS prevalence in the northern province of Pavía, which has a population of 547,251 individuals in 188 municipalities.

When controlling for PM2.5 pollution, participants in urban areas had an increased risk for MS compared with rural dwellers (relative risk [RR], 1.16; 95% CI, 1.04 - 1.30; P = .003)

Recent research has also shown that air pollution is associated with a higher risk for other autoimmune disorders, including systemic lupus erythematosus, rheumatoid arthritis, and type 1 diabetes mellitus.

However, pollution alone is only part of the picture. MS prevalence in highly populated and polluted countries such as China and India is low, with no more than 30 to 40 cases per 100,000 population.

This discrepancy is explained by different genetic backgrounds. While Caucasians are particularly susceptible to MS, Asians are not.