PARIS • Air pollution was fingered for the first time as a major contributor to death and disability caused by stroke, especially in developing nations, in a health review published yesterday.
Air pollution, both indoors from cooking fires and outdoors from traffic fumes, ranked among the top 10 causes of stroke, along with better- known risks such as smoking, high blood pressure and obesity.
A global research team analysed data from other studies, reports and official statistics to create a mathematical model estimating stroke risk for 188 countries from 1990 to 2013.
"A striking finding of our study is the unexpectedly high proportion of stroke burden attributable to environmental air pollution, especially in developing countries," said the study's co-author Valery Feigin of New Zealand's Auckland University of Technology.
The authors said the study was the first to quantify the world's stroke burden in terms of healthy years lost due to people becoming sick, disabled or dying because of stroke.
About 15 million people globally suffer strokes each year, of whom nearly six million die and five million are left disabled - including loss of vision or speech, and paralysis.
Globally - though with huge differences between countries and regions - the top risk factors were high blood pressure, a diet low in fruit, being overweight, eating too much salt, smoking and not eating enough vegetables, said the team.
Ambient pollution came in seventh place and household air pollution from solid fuels ranked eighth. A diet low in whole grains and high blood sugar complete the top 10.
The study found that 90.5 per cent of the stroke burden was attributable to "modifiable factors" - mainly behaviours like smoking, eating too much sugar and not exercising enough, as well as the associated health problems, such as diabetes and heart disease, that these choices result in.
Controlling lifestyle factors, which played a much larger role in rich countries than poor ones, "could prevent about three-quarters of strokes worldwide", said Dr Feigin.
Air pollution was also listed as a "modifiable factor", meaning people or governments can act to change it.
"These findings are important for education campaigns, evidence- based planning, priority setting and resource allocation in stroke prevention," the team wrote in The Lancet Neurology. "Air pollution has emerged as a significant contributor to global stroke burden, especially in low-income and middle-income countries, and therefore, reducing exposure to air pollution should be one of the main priorities to reduce stroke burden in these countries."
In low- and middle-income nations in Asia and Africa, nearly a fifth of the stroke burden was attributed to household air pollution. A similar percentage was blamed on ambient air pollution in China and India.
Air pollution may boost stroke risk by raising blood pressure, hardening blood vessels or causing them to become blocked.