Elsevier

The Lancet Neurology

Volume 15, Issue 9, August 2016, Pages 913-924
The Lancet Neurology

Articles
Global burden of stroke and risk factors in 188 countries, during 1990–2013: a systematic analysis for the Global Burden of Disease Study 2013

https://doi.org/10.1016/S1474-4422(16)30073-4Get rights and content

Summary

Background

The contribution of modifiable risk factors to the increasing global and regional burden of stroke is unclear, but knowledge about this contribution is crucial for informing stroke prevention strategies. We used data from the Global Burden of Disease Study 2013 (GBD 2013) to estimate the population-attributable fraction (PAF) of stroke-related disability-adjusted life-years (DALYs) associated with potentially modifiable environmental, occupational, behavioural, physiological, and metabolic risk factors in different age and sex groups worldwide and in high-income countries and low-income and middle-income countries, from 1990 to 2013.

Methods

We used data on stroke-related DALYs, risk factors, and PAF from the GBD 2013 Study to estimate the burden of stroke by age and sex (with corresponding 95% uncertainty intervals [UI]) in 188 countries, as measured with stroke-related DALYs in 1990 and 2013. We evaluated attributable DALYs for 17 risk factors (air pollution and environmental, dietary, physical activity, tobacco smoke, and physiological) and six clusters of risk factors by use of three inputs: risk factor exposure, relative risks, and the theoretical minimum risk exposure level. For most risk factors, we synthesised data for exposure with a Bayesian meta-regression method (DisMod-MR) or spatial-temporal Gaussian process regression. We based relative risks on meta-regressions of published cohort and intervention studies. Attributable burden for clusters of risks and all risks combined took into account evidence on the mediation of some risks, such as high body-mass index (BMI), through other risks, such as high systolic blood pressure (SBP) and high total cholesterol.

Findings

Globally, 90·5% (95% UI 88·5–92·2) of the stroke burden (as measured in DALYs) was attributable to the modifiable risk factors analysed, including 74·2% (95% UI 70·7–76·7) due to behavioural factors (smoking, poor diet, and low physical activity). Clusters of metabolic factors (high SBP, high BMI, high fasting plasma glucose, high total cholesterol, and low glomerular filtration rate; 72·4%, 95% UI 70·2–73·5) and environmental factors (air pollution and lead exposure; 33·4%, 95% UI 32·4–34·3) were the second and third largest contributors to DALYs. Globally, 29·2% (95% UI 28·2–29·6) of the burden of stroke was attributed to air pollution. Although globally there were no significant differences between sexes in the proportion of stroke burden due to behavioural, environmental, and metabolic risk clusters, in the low-income and middle-income countries, the PAF of behavioural risk clusters in males was greater than in females. The PAF of all risk factors increased from 1990 to 2013 (except for second-hand smoking and household air pollution from solid fuels) and varied significantly between countries.

Interpretation

Our results suggest that more than 90% of the stroke burden is attributable to modifiable risk factors, and achieving control of behavioural and metabolic risk factors could avert more than three-quarters of the global stroke burden. 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.

Funding

Bill & Melinda Gates Foundation, American Heart Association, US National Heart, Lung, and Blood Institute, Columbia University, Health Research Council of New Zealand, Brain Research New Zealand Centre of Research Excellence, and National Science Challenge, Ministry of Business, Innovation and Employment of New Zealand.

Introduction

A comparative assessment of the burden of stroke (in disability-adjusted life-years [DALYs]) attributable to potentially modifiable risk factors between regions and countries is crucial for education campaigns, evidence-based planning, priority setting, and resource allocation in stroke prevention. Understanding of the contribution of each risk factor to changes in stroke burden is important to establish country-specific and region-specific policies for both short-term and long-term population welfare. Documenting how much of the worldwide burden of stroke can be explained by lifestyle, environmental and occupational exposures, and metabolic risk factors allows quantification of the magnitude of stroke burden associated with various risks and prioritisation of preventive strategies at the global, regional, and national levels.

Research in context

Evidence before this study

Disability-adjusted life-years (DALYs) are the most comprehensive measure of population health, and combine the disability and mortality associated with a disease into one metric. We searched Scopus, MEDLINE, and PubMed for reports published in any language up to Dec 31, 2015, using the search terms “stroke” AND “DALY(s)” AND “population-attributable fraction” (PAF) AND “risk factors”. A report from the INTERSTROKE study was based on findings from case-control studies in 22 countries and showed that more than 90% of strokes can be attributed to ten key stroke risk factors. The most recent Global Burden of Disease Study 2013 report provided a global, regional, and national comparative risk assessment of 79 behavioural, environmental and occupational, and metabolic risks factors or clusters of risk factors in 188 countries from 1990 to 2013, but did not analyse in detail the stroke burden attributable to risk factors.

Added value of this study

To our knowledge this study is the first to quantify stroke burden in terms of DALYs and report changes in burden attributable to 17 potentially modifiable behavioural, environmental and occupational, and metabolic risks or clusters of risks at the global, regional, and country levels from 1990 to 2013. The study showed that 90·5% (95% UI 88·5–92·2) of the global burden of stroke was attributable to the modifiable risk factors analysed, including 74·2% (95% UI 70·7–76·7%) to behavioural factors (ie, smoking, poor diet, and low physical activity). Clusters of metabolic factors (high systolic blood pressure, high body-mass index, high fasting plasma glucose, high total cholesterol, and low glomerular filtration rate) and environmental factors (air pollution and lead exposure) were the second and third largest contributors to DALYs. For the first time, air pollution emerged as one of the leading contributors to stroke burden worldwide, accounting for 29·2% of the stroke-related DALYs. Globally, the PAF of all risk factors to the burden of stroke increased with time (except for second-hand smoking and household air pollution from solid fuels) and varied significantly between countries and regions.

Implications of all the available evidence

These findings are important for education campaigns, evidence-based planning, priority setting (including for stroke research), and resource allocation in stroke prevention. Understanding the contribution of each risk factor and risk cluster to the changes in stroke burden is important to establish country-specific and region-specific policies on stroke prevention strategies. Although the proportion of the stroke burden of risk clusters provides a broad view of investment priorities, stroke burden due to individual risks in different age groups of the population can inform the potential elements of a more specific intervention. For example, reducing exposure to air pollution should be one of the main priorities to reduce stroke burden in low-income and middle-income countries, whereas reduction of behavioural risks should be one of the main priorities in high-income countries. For future research, the next step is to close the knowledge gap on stroke burden. This would include identification of previous health conditions grouped by age, sex, and stroke subtype, in addition to the regular monitoring of stroke incidence, mortality, prevalence, associated disability, and modifiable risk factors.

Previously, we reported on 79 behavioural, environmental and occupational, and metabolic risks or clusters of risks for diseases, including all cardiovascular disease, in 188 countries from 1990 to 2013.1 In this Article, we report estimates from the Global Burden of Disease Study 2013 (GBD 2013) for population-attributable fraction (PAF) of stroke-related DALYs associated with potentially modifiable environmental and occupational, behavioural, and physiological, and metabolic risk factors by age groups globally, in high-income countries, and in low-income and middle-income countries as defined by the World Bank, from 1990 to 2013. We also report PAF of stroke-related DALYs associated with behavioural, environmental, and metabolic risk clusters by sex, globally, and regions in 2013.

Section snippets

Overview

Details about the basic approach for the GBD 2013 estimates of the PAF and burden of stroke have been reported previously.1, 2, 3, 4, 5 Briefly, we used published and unpublished data on the distribution of risks to estimate the fraction of the population in each country, age group, and year exposed to different levels of risk factors, when evidence of a causal and biologically plausible association between exposure to the risk factor and the incidence of stroke was convincing.1 GBD 2013

Results

Globally, 90·5% of the burden of stroke (as measured in DALYs) was attributable to the modifiable risk factors analysed (table). Although, in most countries worldwide, stroke burden from all these risk factors combined varied between 80% and 97%; in most African countries, it varied between 72% and 79% (figure 1). Of the total stroke-related DALYs, 74·2% (83·8 million DALYs) were due to behavioural factors (ie, smoking, poor diet, and low physical activity) and 72·4% (81·7 million DALYs) were

Discussion

Our results show the global, regional, and country-specific burden of stroke (as measured with DALYs) associated with potentially modifiable risk factors and risk factor clusters from 1990 to 2013. For the first time, air pollution has emerged as one of the leading contributors to stroke burden worldwide, accounting for almost a third of stroke-related DALYs. Our findings suggest that more than 90% of the global burden of stroke in 2013 was attributable to the combined effect of all modifiable

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