The Lancet Study Finds Particulate Matter air pollution to be at par with smoking in contributing to subarachanoid haemorrhage
Although stroke is highly preventable and treatable, there has been a rapid rise in the global stroke burden between 1990 and 2021, due to both population growth and the rise of aging populations worldwide, as well as a substantial increase in people’s exposure to environmental and behavioural risk factors. The findings of this major new analysis from the Global Burden of Disease, Injuries, and Risk Factors Study (GBD) were published in The Lancet Neurology journal and were presented at the World Stroke Congress in Abu Dhabi in October 2024.
The current study builds on previous GBD analyses to provide the most up-to-date and comprehensive analysis of stroke burden and risk factor estimates in countries on a global scale between 1990 and 2021, to help guide health-planning, prevention, and resource allocation.
Lead author Professor Valery L Feigin from Auckland University of Technology, New Zealand, an affiliate professor at the Institute for Health Metrics and Evaluation (IHME) at the University of Washington, USA, said: “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. 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.”
The study reveals striking differences in the overall stroke burden (as measured by age-standardised incidence, prevalence, death and DALY rates) between world regions and national income levels in 2021. In high-income North America and Australasia, and middle-income Latin America—regions with the lowest stroke burden—the age-standardised rates of incidence and prevalence were lowest in New Zealand (67.8 and 707.4 per 100,000 people respectively), death rates lowest in Canada (20.4 per 100,000 people), and DALY rates lowest in Australia (435.0 per 100,000) in 2021.
In contrast, in the regions of low- and middle-income East and Central Asia and sub-Saharan Africa, the rates of incidence, prevalence, death and DALYs were up to 2 to 10 times higher (over 248, 1458, 190, and 4320 per 100,000 people, respectively) in 2021.
Strikingly, half of all the disability and the lives lost to stroke globally (81 million healthy years of life lost) in 2021 were the result of haemorrhagic strokes—the deadliest form, mainly due to high blood pressure—despite being around half as common as ischaemic strokes (4.1 million new haemorrhagic strokes vs 7.8 million new ischaemic strokes). Most affected were people aged 70 and younger and those living in low-income countries, where the proportion of strokes that are intracerebral haemorrhage is double that of high-income countries (37% vs 18%).
“Stroke-related health loss disproportionately impacts many of the most disadvantaged countries in Asia and sub-Saharan Africa due to the growing burden of uncontrolled risk factors, especially poorly controlled high blood pressure, and rising levels of obesity and type 2 diabetes in young adults, as well as the lack of stroke prevention and care services in these regions,” explained co-author Dr Catherine O. Johnson, Lead Research Scientist at IHME. “The shift in stroke burden towards younger populations is likely to continue unless effective preventive strategies are implemented urgently.”
The study estimates that the total number of stroke-related DALYs attributable to 23 risk factors [3] globally has risen from 100 million years of healthy life lost in 1990 to 135 million in 2021—presenting a public health challenge and an opportunity for action. The largest proportions of these risk factors are found in Eastern Europe, Asia, and sub-Saharan Africa.
Metabolic risk factors—especially high BMI, high systolic blood pressure, and high LDL cholesterol—contributed to the most stroke burden across all country income levels (ranging from 66-70%) in 2021, followed by environmental risk factors collectively (i.e., air pollution, low/high ambient temperature, lead exposure) in LMICs (35-53%).
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 (see figure 2).
For the first time, the study suggests that ambient particulate matter air pollution is a top risk factor for subarachnoid haemorrhage, contributing to 14% of the death and disability caused by this serious stroke subtype, on a par with smoking (see figure 2).
In contrast, substantial progress has been made in reducing the global stroke burden from risk factors linked to poor diet, air pollution, and smoking, with health loss due to diets high in processed meat and low in vegetables declining by 40% and 30%, respectively, particulate matter air pollution by 20%, and smoking by 13%. This suggests that strategies to reduce exposure to these risk factors over the past three decades, such as clean air zones and public smoking bans, have been successful.
“With 84% 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,” said Dr Johnson. “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. 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. 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.”
As Professor Feigin explained: “Additional and more effective stroke prevention strategies, with an emphasis on population-wide measures, such as task-shifting from doctors to nurses and health volunteers, and the wider use of evidence-based mobile and telehealth platforms, along with pragmatic solutions to address the critical gaps in stroke service delivery, workforce capacity building, and epidemiological surveillance systems must be urgently implemented across all countries.”
Reference: Feigin, V. L., et al. (2024). Global, regional, and national burden of stroke and its risk factors, 1990–2021: A systematic analysis for the Global Burden of Disease Study 2021. The Lancet Neurology, 23(10), 973-1003. https://doi.org/10.1016/S1474-4422(24)00369-7
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