Does Air Pollution Affect the Risk of Stroke?

The World Health Organization (WHO) recently published data on air pollution in various cities across the world focussing on airborne particles smaller than 2.5 micrometers known as PM2.5. The report ranked cities after studying their air for the presence of harmful gases, such as nitrogen dioxide, carbon monoxide and sulphur dioxide, besides particulate matter (PM) 10 and 2.5. 13 of the world's 20 most polluted cities are in India, New Delhi being the most polluted of all. Smaller airborne particles or particulate matter is among the most dangerous of all these pollutants. New Delhi, Patna, Gwalior, Raipur, Ahmedabad, Lucknow, Kanpur, Amritsar, Ludhiana, Allahbad, Agra and Khanna are included among the top 20 most polluted cities in the world. 

High levels of air pollution has been linked to increased rate of chronic bronchitis, lung cancer and heart disease. Long term exposure to air pollution has also been associated with higher risk of stroke and impaired cognition. Following are the effects of air pollution on brain and central nervous system:

• Increased risk of carotid atherosclerosis
• Decreased cognition in older people
• Every 2 microgram per meter cube increase in PM 2.5 leads to 1 year of accelerated brain aging and atrophy (degeneration)
• Increased risk of death from stroke among people living in areas with high air pollution, especially in people aged >60 years and non-smokers
•  In Tokyo, the risk increase for subarachnoid hemorrhage mortality per 10 μg/m3 PM2.5 or NO2 has been associated with double the risk increase for ischemic or intracerebral hemorrhage mortality
•  Stronger associations between short-term air pollution exposure and stroke mortality are observed in elderly, women, and individuals with a history of diabetes mellitus or cardiac disease
• Air pollution on warm days has been more strongly associated with both hemorrhagic and ischemic stroke