Environmental, Metabolic Factors Driving Rise in Stroke

Air pollution, high temperatures, and metabolic risk factors are driving global increases in stroke, contributing to 12 million cases and more than 7 million deaths from stroke each year, new data from the Global Burden of Disease (GBD) study showed.

Between 1990 and 2021, the number of people who experienced a stroke increased to 11.9 million (up by 70% since 1990), while the number of stroke survivors rose to 93.8 million (up by 86%), and stroke-related deaths rose to 7.3 million (up by 44%), making stroke the third leading cause of death worldwide after ischemic heart disease and COVID-19, investigators found.

Stroke is highly preventable, the investigators noted, with 84% of the stroke burden in 2021 attributable to 23 modifiable risk factors, including air pollution, excess body weight, high blood pressure, smoking, and physical inactivity.

This means there is “tremendous opportunities to alter the trajectory of stroke risk for the next generation,” Catherine O. Johnson, MPH, PhD, co-author and lead research scientist at the Institute for Health Metrics and Evaluation (IHME), University of Washington, Seattle, said in a news release.

The study was published online on September 18 in The Lancet Neurology.

Top Risk Factor for Subarachnoid Hemorrhage

Since 1990, the contribution of high temperatures to poor health and early death due to stroke has risen 72%, a trend likely to increase in the future — underscoring the impact of environmental factors on the growing stroke burden, the authors said.

“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,” Johnson said.

Mitchell S.V. Elkind, MD, MS, chief clinical science officer for the American Heart Association, who wasn’t involved in the study, told Medscape Medical News that environmental factors such as air pollution, particulate matter from wildfires and other sources, and excessive heat are now recognized as major contributors to the risk for stroke. “This should not be surprising as we have long recognized the risks of stroke associated with toxins in cigarette smoke, which likely share mechanisms for vascular damage with pollutants,” Elkind said.

The data also reveal for the first time that ambient particulate matter air pollution is a top risk factor for subarachnoid hemorrhage, contributing to 14% of the death and disability caused by this serious stroke subtype, on a par with smoking.

Elkind noted that smoking is “a major risk factor for subarachnoid hemorrhage. It makes sense that particulate air pollution would therefore similarly be a risk factor for subarachnoid hemorrhage, which similarly damages blood vessels. Prior studies were likely too small or did not assess the role of air pollution in subarachnoid hemorrhage.”

The analysis also showed substantial increases between 1990 and 2021 in the global stroke burden linked to high body mass index (up by 88%), high blood sugar (up 32%), a diet high in sugar-sweetened drinks (up 23%), low physical activity (up 11%), high systolic blood pressure (up 7%), and a diet low in omega-6 polyunsaturated fatty acids (up 5%).

“And with increasing exposure to risk factors such as high blood sugar and diet high in sugar-sweetened drinks, there is a critical need for interventions focused on obesity and metabolic syndromes,” Johnson said.

“Identifying sustainable ways to work with communities to take action to prevent and control modifiable risk factors for stroke is essential to address this growing crisis,” she added.

Prevention Strategies Fall Short

The data also showed that stroke-related disability-adjusted life-years rose from around 121.4 million years of healthy life lost in 1990 to 160.5 million years in 2021, making stroke the fourth leading cause of health loss worldwide after COVID-19, ischemic heart disease, and neonatal disorders.

“The global growth of the number of people who develop stroke and died from or remain disabled by stroke is growing fast, strongly suggesting that currently used stroke prevention strategies are not sufficiently effective,” lead author Valery L Feigin, MD, PhD, from Auckland University of Technology, Auckland, New Zealand, and affiliate professor at IHME, said in the release.

“New, proven effective population-wide and motivational individual prevention strategies that could be applied to all people at risk of having a stroke, regardless of the level of risk, as recommended in the recent Lancet Neurology Commission on Stroke should be implemented across the globe urgently,” said Feigin.

Elkind said the AHA supports research on the effects of air quality on risk for vascular injury and stroke and has “long advocated for policies to mitigate the adverse health impacts of air pollutants, including reduction of vehicle emissions and renewable portfolio standards, taking into account racial, ethnic and economic disparities.”

“AHA, and the healthcare sector more broadly, must take a leadership role in recommending policies to improve environmental air quality and in working with the private sector and industry to improve air quality,” Elkind said.

In an accompanying commentary, Ming Liu, MD, and Simiao Wu, MD, PhD, West China Hospital, Sichuan University, Chengdu, China, wrote that “pragmatic solutions to the enormous and increasing stroke burden include surveillance, prevention, acute care, and rehabilitation.”

“Surveillance strategies include establishing a national-level framework for regular monitoring of stroke burden, risk factors, and healthcare services via community-based surveys and health records,” they noted.

“Artificial intelligence and mobile technologies might not only facilitate the dissemination of evidence-based health services but also increase the number of data sources and encourage participation of multidisciplinary collaborators, potentially improving the validity and accuracy of future GBD estimates,” they added.

This study was funded by the Bill & Melinda Gates Foundation. Author disclosures are listed with the original article.