Air Pollution May Double the Risk of Stroke

A stroke is the loss of brain function due to an interruption in the flow of blood to all or part of the brain. Strokes are the third leading cause of death in the USA, and a leading cause of permanent disability. There are two kinds of stroke: ischemic, caused by a clot that has traveled to the brain or within the brain and blocked the flow of blood, and hemorrhagic, caused by the rupture of a blood vessel within the brain. Ischemic stroke is the most common type, accounting for almost 80% of all strokes; the remaining 20% are hemorrhagic.

A report from Japan in Occupational and Environmental Medicine has demonstrated that the levels of air pollutants play an important role in the incidence of stroke. Stroke deaths in people over 65 during a four-year period were analyzed, and set in relation to the air pollutants nitrogen oxide, particulate matter, and photochemical oxidants in 13 different areas. First thee scientists noted a peak in intracerebral hemorrhage stroke deaths in the warm months between April and September. Then they found an association between a high hourly rate of particulate matter (more than 200 micrograms/cubic mm) around 2 hours before death; there was in fact a doubling of the risk of death.

There was no association between hemorrhagic stroke and the 24-hour particulate matter level, and no association between pollutants and ischemic stroke. It seems very clear, therefore, that the higher levels of particulate manner are directly responsible for the doubled risk.