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.