Air Pollution and stroke Discussion

 

Discussion

In this systematic review and meta-analysis, we 

evaluated the effects of short term exposure to gaseous and particulate air pollution on admission to hospital for stroke or mortality from stroke. We made several important observations. Firstly, in over 6.2 million events across 28 countries throughout the world, our pooled analysis showed 

robust and clear associations between both gaseous and particulate air pollution and stroke admission or mortality. Secondly, the strongest associations between air pollution and admission or mortality were observed from studies originating in low to middle income countries. Thirdly, these associations persisted when we stratified our pooled 

analyses by study design, age, or outcome. Thus, we have shown that gaseous and particulate air pollutants have a robust and close temporal association with admission to hospital for stroke or stroke death. We suggest that improvements in air quality could reduce the burden of stroke.

Evidence of short term exposure to air pollution and stroke

Over the past three decades, epidemiological studies including pooled analyses have shown that cardiac, rather than pulmonary, disease is the primary cause of morbidity and mortality associated with exposure to air pollution.36 Long term exposure studies have already shown strong associations between air pollution and stroke.37 38 39 While the short term effects of air pollution on cardiac disease, including heart failure and myocardial infarction, have received much attention, it is less certain whether acute exposure to air pollution is a trigger for cerebrovascular disease, especially stroke.3 4 11 This is partly because the results of many short term exposure studies evaluating the effect of air pollution on stroke have been inconclusive, reflecting both the nature of the condition and the size of individual studies.36 Recently meta-analyses, including 12 and 45 studies, reported an association between particulate air pollution and stroke.40 41 42 43 To our knowledge, our study is the first comprehensive prespecified pooled analysis to examine the short term effects after exposure to gaseous or particulate air pollution and admission to hospital for stroke or mortality from stroke across both time series and case crossover study designs.

Particulate matter and gaseous pollutants both showed a strong temporal relation with mortality from stroke and admission to hospital for stroke. The lag effects of exposure and stroke have to be interpreted with caution. Unlike other cardiac conditions such as acute myocardial infarction, decompensated heart failure, and sudden cardiac death, the timing of onset of stroke symptoms and subsequent admission to hospital or mortality might differ substantially.44 Lokken and colleagues showed that in cases of acute ischaemic stroke, onset of symptoms occurred at a median of one calendar day before admission, and this delay in presentation is likely to underestimate the overall association between exposure to pollutant and stroke.44

Ref

 BMJ. 2015 Mar 24;350:h1295. doi: 10.1136/bmj.h1295

Short term exposure to air pollution and stroke: systematic review and meta-analysis

Anoop S V Shah 1,✉, Kuan Ken Lee 1, David A McAllister 2, Amanda Hunter 1, Harish Nair 2, William Whiteley 3, Jeremy P Langrish 1, David E Newby 1, Nicholas L Mills