Almost one in three strokes are triggered by air pollution, alarming research has revealed.

The worldwide study named the environmental hazard as a major cause of one of the leading causes of death for the first time.

Air pollution, both inside from cooking fires and outside from traffic fumes, ranked among the top ten causes of stroke, along with better known risks such as smoking, high blood pressure and obesity.

Microscopic particles, much of which is generated by diesel exhausts, have been shown to cause clotting, which can lead to a stroke.

Stroke claims six million lives annually and many survivors suffer paralysis, speech problems and personality changes as a result.

The New Zealand-led research analysed data from 188 countries to estimate the proportion of strokes that could be avoided if certain risks were avoided.

It found 70 per cent of strokes could be prevented by lifestyle changes such as giving up cigarettes, eating more fruit and vegetables and doing more exercise.

Overall, 30 per cent of global disability associated with stroke is linked to air pollution.

This is especially high in developing countries where the burden is 33.7 per cent compared to 10.2 per cent in developed countries.

In low and middle-income nations in Asia and Africa, almost a fifth of stroke burden was attributed to household air pollution, while a similar percentage was blamed on outside air pollution in China and India.

In 2013, 17 per cent of global stroke cases were attributed to environmental air pollution, the Lancet Neurology study revealed.

This is measured by tiny particles of soot or dust from traffic fumes and factories, fine particle matter known as PM 2.5.

This was almost as much as that from smoking (21 per cent).

“A striking finding of our study is the unexpectedly high proportion of stroke burden attributable to environmental air pollution, especially in developing countries,” said study co-author Valery Feigin of New Zealand’s Auckland University of Technology.

Professor Vladimir Hachinski, of the University of Western Ontario, reviewed the research.

He said: “The most alarming finding was that about a third of the burden of stroke is attributable to air pollution.

“Although air pollution is known to damage the lungs, heart, and brain, the extent of this threat seems to have been underestimated. Air pollution is not just a problem in big cities, but is also a global problem.

“With the ceaseless air streams across oceans and continents, what happens in Beijing matters in Berlin.”

He added: “Air pollution is one aspect of the fossil fuel and global warming problem, which is itself partly a result of westernisation and urbanisation, especially in India and China.”

Meanwhile, being fit in your 40s could cut your risk of a stroke in your 60s.

Research has shown that men and women who are very fit in their mid to late 40s are a third less likely to suffer a stroke aged 65-plus than their couch-potato friends and colleagues.

The University of Texas researchers analysed data on almost 20,000 men and women.

These people had been put through a fitness test on a treadmill between the ages of 45 and 50 and had their health tracked until they were at least 65.

The fittest 40 per cent in middle-age were 37 per cent less likely than the least fit to suffer a stroke in old age.

The result held even when factors such as diabetes and high blood pressure were taken into account.

Writing in the journal Stroke, they said that exercise may boost blood flow to the brain, staving off the natural decay of brain tissue.

“In 1900, only about 15 per cent of the world’s population lived in cities; now more than half the world’s population does.

“In cities, particularly in megacities with more than10 million inhabitants, getting unhealthy food is easy and getting exercise is hard, emphasising the difficulty of achieving a healthy lifestyle in an unhealthy environment.”

Professor Feigin said it was now the responsibility of governments to address these stroke triggers through legislation and taxation of tobacco, alcohol, salt, sugar and saturated fat content.

By By Chukwuma Muanya

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