Burton J. Tabaac, MD
A study in 2010, published in INTERSTROKE, detailed the risk factors for stroke in 22 countries. It was shown that 90% of all ischemic and hemorrhagic strokes can be attributed to 10 major risk factors, hypertension and current smoking being the most prominent.1 This current meta-analytical article, written by Scheers et al, analyzed the Pubmed citation database to quantify the pooled association between stroke incidence and mortality with long-term exposure to particulate matter. This meta-analysis suggests a statistically significant effect of recent particulate matter exposure and the risk of stroke.
The article incorporates 20 publications, including more than 10 million people, and more than 200,000 stroke events to reveal that the association between long-term particulate matter exposure and stroke event was positive in North America and Europe (but not statistically significant for the latter) and null in Asia. The authors are keen to differentiate recent and long-term exposure to particulate matter, as they are different pathophysiological concepts. The study focus regarding short-term exposure asks when strokes are most likely to occur, whereas the consideration pertaining to long-term exposure focuses on where people are at risk.
In discussing the biological mechanisms of ambient air pollution in causing cardiovascular disease, the researchers underscore that chronic inhalation of pollutants may cause chronic pulmonary and systemic oxidative stress and inflammation. This pathway leads to endothelial dysfunction, vasoconstriction, and atherosclerosis at the vasculature level, as well as coagulation and thrombosis at the blood-tissue level.2 Neurons have been shown to be vulnerable to long-term particulate matter exposure because the blood-brain barrier becomes impaired, either directly after having penetrated into the circulatory system or indirectly via inflammatory processes aforementioned.3
A study conducted in 2010 by the Global Burden of Disease provided the statistics on attributable deaths and disability-adjusted life years for 67 risk factors, including environmental air pollution.4 This paper builds on the previous literature to highlight that 3.7 million deaths worldwide and 3.1% of global disability-adjusted life years are attributed to air pollution. This fact places air pollution, and specifically particulate matter, in the top ten of potential risk factors. Cardiovascular, and circulatory diseases such as stroke, account for the majority of deaths attributed to air pollution. The scientific evidence for the past decade has identified the relationship between long-term exposure to particulate matter and stroke, but this current paper raises a question as to the unexplained geographical variability in that association.
- O’Donnell MJ, Xavier D, Liu L, Zhang H, Chin SL, Rao-Melacini P, et al; INTERSTROKE Investigators. Risk factors for ischaemic and intracerebral haemorrhagic stroke in 22 countries (the INTERSTROKE study): a case-control study. Lancet. 2010;376:112–123. doi: 10.1016/S0140-6736(10)60834-3.
- Brook RD, Rajagopalan S, Pope CA III, Brook JR, Bhatnagar A, Diez-Roux AV, et al; American Heart Association Council on Epidemiology and Prevention, Council on the Kidney in Cardiovascular Disease, and Council on Nutrition, Physical Activity and Metabolism. Particulate matter air pollution and cardiovascular disease: an update to the scientific statement from the American Heart Association. Circulation. 2010;121:2331–2378. doi: 10.1161/CIR.0b013e3181dbece1.
- Genc S, Zadeoglulari Z, Fuss SH, Genc K. The adverse effects of air pollution on the nervous system. J Toxicol. 2012;2012:782462.
- GBD 2010 Mortality and Causes of Death Collaborators. A comparative risk assessment of burden of disease and injury attributable to 67 risk factors and risk factor clusters in 21 regions, 1990–2010: a systematic analysis for the Global Burden of Disease Study 2010. Lancet. 2012;380:2224–60.