The challenge in linking air pollution to age-related disease and mortality risk lies in the confounding correlation with wealth. There are plausible mechanisms involving, for example, increased levels of inflammation resulting from high levels of air pollution, but regions with lower levels of air pollution tend to have much wealthier populations, and it is well known that wealth correlates with greater life expectancy, both for individuals and in societies as a whole. This study adds more statistical data to the mix:
Air pollution - including environmental and household air pollution - has emerged as a leading risk factor for stroke worldwide, associated with about a third of the global burden of stroke in 2013. The findings, from an analysis of global trends of risk factors for stroke between 1990-2013, also show that over 90% of the global burden of stroke is linked to modifiable risk factors, most of which (74%) are behavioural risk factors such as smoking, poor diet and low physical activity. The authors estimate that control of these risk factors could prevent about three-quarters of all strokes. The study is the first to analyse the global risk factors for stroke in such detail, especially in relation to stroke burden on global, regional and national levels. The researchers used data from the Global Burden of Disease Study to estimate the disease burden of stroke associated with 17 risk factors in 188 countries. They estimated the population-attributable fraction (PAF) of stroke-related disability-adjusted life years (DALYs) - ie. the estimated proportion of disease burden in a population that would be avoided if exposure to a risk factor were eliminated.
Globally, the ten leading risk factors for stroke were high blood pressure, diet low in fruit, high body mass index (BMI), diet high in sodium, smoking, diet low in vegetables, environmental air pollution, household pollution from solid fuels, diet low in whole grains, and high blood sugar. About a third (29.2%) of global disability associated with stroke is linked to air pollution (including environmental air pollution and household air pollution). This is especially high in developing countries (33.7% vs 10.2% in developed countries). In 2013, 16.9% of the global stroke burden was attributed to environmental air pollution (as measured by ambient particle matter pollution of aerodynamic diameter smaller than 2·5 μm) - almost as much as that from smoking (20.7%). From 1990 to 2013, stroke burden associated with environmental air pollution has increased by over 33%.