For the first time, a study on Thursday showed that ambient particulate matter air pollution is a top risk factor for subarachnoid haemorrhage — a type of brain stroke — at par with smoking.

The study, led by an international team of researchers from India, the US, New Zealand, Brazil, and UAE showed that air pollution contributed to 14 per cent of the death and disability caused by this serious stroke subtype, on par with smoking.

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The study showed that coupled with air pollution, high temperatures as well as metabolic disorders, fuelled a significant rise in global cases and deaths due to stroke in the last three decades.

The number of people worldwide having a new stroke rose to 11.9 million in 2021 — up by 70 per cent since 1990. Stroke-related deaths rose to 7.3 million — up by 44 per cent since 1990.

The study identified 23 modifiable risk factors responsible for 84 per cent of the stroke burden in 2021.

In 2021, the five leading global risk factors for stroke were high systolic blood pressure, particulate matter air pollution, smoking, high LDL cholesterol, and household air pollution, with considerable variation by age, sex, and location.

It also showed substantial progress made in reducing the global stroke burden by reducing particulate matter air pollution (20 per cent), and smoking (13 per cent).

“With 84 per cent of the stroke burden linked to 23 modifiable risk factors there are tremendous opportunities to alter the trajectory of stroke risk for the next generation. Given that ambient air pollution is reciprocally linked with ambient temperature and climate change, the importance of urgent climate actions and measures to reduce air pollution cannot be overestimated,” said co-author Dr Catherine O. Johnson, Lead Research Scientist at the University of Washington’s Institute for Health Metrics and Evaluation (IHME).

While stroke is now the third leading cause of death worldwide (after ischaemic heart disease and Covid-19), the condition is highly preventable and treatable.

The researchers called for identifying sustainable ways to work with communities to take action to prevent and control modifiable risk factors such as high blood sugar and a diet high in sugar-sweetened drinks. There is a critical need for interventions focused on obesity and metabolic syndromes, Johnson said.

They also called for measures such as clean air zones and public smoking bans, which have been successful.

The findings based on the Global Burden of Disease, Injuries, and Risk Factors Study (GBD) showed that more than three-quarters of those affected by strokes live in low- and middle-income countries (LMICs).

The study also found that worldwide, the overall amount of disability, illness, and early death — a measurement known as disability-adjusted life years (DALYs) — lost to stroke increased by 32 per cent between 1990 and 2021, rising from around 121.4 million years of healthy life lost in 1990 to 160.5 million years in 2021.