Air pollution and MS


We know that smoking, passive smoking and solvent exposure increase your risk of getting MS. The hypothesis, supported by animal work, suggests these risk factors alter antigens or proteins in the lung that then trigger autoimmunity. In other words, the altered proteins are interpreted as being foreign by the immune system. 

Particulate air pollution is another respiratory toxin that has been studied in Iran and is associated with an increased prevalence of MS. I suspect that particulate matter air pollution also increases your risk of getting MS based on similar mechanisms to smoking and solvent exposure. 

Another aspect of particulate matter air pollution exposure is that it drives comorbidities and is therefore likely to make MS progress more quickly. The second paper (below) in this week’s BMJ is quite shocking in that it shows you how high the health burden is for particulate air pollution, at a general population level. Is there anything we can do about this? Yes, there is. We need to nudge our politicians whenever we can to enact legislation to clean up the air that we have to breathe.  I am aware that there are retrograde steps in the US to reverse some of the clean air legislation; this should be resisted. My heart goes out to people living in low- and middle-income countries who will have to wait for a generation or two to get to the point when air pollution drops to safer levels.

Why should people with MS be exposed to unnecessarily high levels of air pollution that are likely to make their MS worse? 

Why should people at high risk of getting MS, be exposed to environmental pollutants that may push them over the “autoimmune tipping point” resulting in them developing MS?

Part of our lifestyle and wellness campaign is focusing on environmental health; air pollution is one of the things that impact wellness. Our marginal gains management philosophy has just acquired another component; environmental pollution. Do you agree? 

Heydarpour  et al. Potential impact of air pollution on multiple sclerosis in Tehran, Iran. Neuroepidemiology. 2014;43(3-4):233-8.

BACKGROUND: Multiple sclerosis (MS) incidence has dramatically increased in Tehran, Iran. The health impact of air pollution in Tehran underscores the attention to a possible association to this environmental risk factor. In this study, the authors aimed to analyze the spatial distribution of prevalent MS cases and their association with the spatial patterns of air pollution.

METHODS: Patient records meeting McDonald’s criteria for definite MS diagnosis with disease onset during 2003-2013 were obtained. Next, the location of 2,188 patients was successfully geo-referenced within Tehran metropolis by geographic information system (GIS) bureau of Iran’s post office based on their phone numbers. A cluster analysis was performed using the average nearest neighbor index (ANNI) and quadrat analysis. The long-term exposures of MS patients to particulate matter (PM10), sulfur dioxide (SO2), nitrogen oxide (NO), nitrogen dioxide (NO2), and nitrogen oxides (NOx) were estimated using the previously developed land use regression models.

RESULTS: Prevalent MS cases had a clustered pattern in Tehran. A significant difference in exposure to PM10, SO2, NO2, and NOx (p < 0.001) was observed in MS cases compared with controls.

CONCLUSION: This study revealed the potential role of long-term exposure to air pollutants as an environmental risk factor in MS.

Wei et al. Short term exposure to fine particulate matter and hospital admission risks and costs in the Medicare population: time stratified, case-crossover study. BMJ. 2019 Nov 27;367:l6258. doi: 10.1136/bmj.l6258.

OBJECTIVE: To assess risks and costs of hospital admission associated with short term exposure to fine particulate matter with diameter less than 2.5 µm (PM2.5) for 214 mutually exclusive disease groups.

DESIGN: Time stratified, case-crossover analyses with conditional logistic regressions adjusted for non-linear confounding effects of meteorological variables.

SETTING: Medicare inpatient hospital claims in the United States, 2000-12 (n=95 277 169).

PARTICIPANTS: All Medicare fee-for-service beneficiaries aged 65 or older admitted to hospital.

MAIN OUTCOME MEASURES: Risk of hospital admission, number of admissions, days in hospital, inpatient and post-acute care costs, and value of statistical life (that is, the economic value used to measure the cost of avoiding a death) due to the lives lost at discharge for 214 disease groups.

RESULTS: Positive associations between short term exposure to PM2.5 and risk of hospital admission were found for several prevalent but rarely studied diseases, such as septicemia, fluid and electrolyte disorders, and acute and unspecified renal failure. Positive associations were also found between risk of hospital admission and cardiovascular and respiratory diseases, Parkinson’s disease, diabetes, phlebitis, thrombophlebitis, and thromboembolism, confirming previously published results. These associations remained consistent when restricted to days with a daily PM2.5 concentration below the WHO air quality guideline for the 24 hour average exposure to PM2.5. For the rarely studied diseases, each 1 µg/m3 increase in short term PM2.5 was associated with an annual increase of 2050 hospital admissions (95% confidence interval 1914 to 2187 admissions), 12 216 days in hospital (11 358 to 13 075), US$31m (£24m, €28m; $29m to $34m) in inpatient and post-acute care costs, and $2.5bn ($2.0bn to $2.9bn) in value of statistical life. For diseases with a previously known association, each 1 µg/m3 increase in short term exposure to PM2.5 was associated with an annual increase of 3642 hospital admissions (3434 to 3851), 20 098 days in hospital (18 950 to 21 247), $69m ($65m to $73m) in inpatient and post-acute care costs, and $4.1bn ($3.5bn to $4.7bn) in value of statistical life. 

CONCLUSIONS: New causes and previously identified causes of hospital admission associated with short term exposure to PM2.5 were found. These associations remained even at a daily PM2.5 concentration below the WHO 24 hour guideline. Substantial economic costs were linked to a small increase in short term PM2.5.

About the author

Prof G

Professor of Neurology, Barts & The London. MS & Preventive Neurology thinker, blogger, runner, vegetable gardener, husband, father, cook and wine & food lover.


  • I seem to remember something on this blog about how Epstein Barr virus acts on the same pathway as smoking, so that, if a person has Epstein Barr, smoking confers no additional risk of developing MS. Am I mistaken? (Although smoking is obviously still going to increase the impact of comorbidities.)

  • I walk to and from work, it takes half an hour each way, at a fairly fast pace.

    I try and walk the back roads when possible, to keep away from traffic pollution, and start the walk at 6.50am, there is some traffic but not rush hour traffic.
    I’ve been thinking of buying a mask for walking at rush hour times, on my way home.

    The benefits of walking for me are great, I really feel it has helped keep me pain free.

  • A footnote in Siddhartha Mukherjee’s book ‘The Gene’ says:
    In the 1970s, the reigning theory of carcinogenesis was that all, or most, cancers were caused by viruses. Pathbreaking experiments performed by several scientists, including Harold Varmus and J. Michael Bishop at UCSF, revealed, surprisingly, that these viruses typically caused cancer by tampering with cellular genes—called proto-oncogenes. The vulnerabilities, in short, were already present within the human genome. Cancer occurs when these genes are mutated, thereby unleashing dysregulated growth.

    Could there be something similar happening in MS?
    That a vulnerability exists in the genome, and a trigger causes a mutation that leads to MS

    And could there be a range of possible triggers?
    For some it could be air pollution, for orhers it coukd be EBV, or some other virus,

    • Multiple sclerosis (MS) incidence has dramatically increased in Tehran, Iran.

      It has since the Iranian revolution and the subsequent widespread re-imposition of the veiling of women, with a corresponding precipitous drop in vitamin D levels in women in a country where sunlight is in abundance.

By Prof G



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