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Global, regional and national comparative risk assessment of 79 behavioural, environmental and occupational, and metabolic risks or clusters of risks in 195 countries, 1990-2015: a systematic analysis for the Global Burden of Disease Study 2015

The Lancet. 2016. Vol. 388. No. 10053. P. 1-37.

The Global Burden of Diseases, Injuries, and Risk Factors Study 2015 (GBD 2015) provides an up to date synthesis of the evidence on risk factor exposure and the burden of disease attributable to these risks. By providing national and subnational assessments spanning 25 years, the GBD 2015 can help inform debates on the importance of addressing different risks in different contexts.
We used the comparative risk assessment (CRA) framework developed for previous iterations of the GBD study to estimate attributable deaths, DALYs, and trends in exposure by age group, sex, year, and geography for 79 behavioural, environmental and occupational, and metabolic risks or clusters of risks over the period 1990 to 2015. The GBD 2015 study included 388 risk-outcome
pairs which met World Cancer Research Fund-defined criteria for convincing or probable evidence. Relative risk estimates were extracted from published and unpublished randomised controlled trials, cohorts, and pooled cohorts. Risk exposures were estimated based on published studies, household surveys, census data, satellite data, and other sources. Statistical models were used to pool data from different sources, adjust for bias in the data, and incorporate explanatory covariates. We developed a metric that allows comparisons of exposure across risk factors – the summary exposure value (SEV) – which is scaled so that 100% is the entire population at maximum risk, and 0% is everyone at lowest risk. Using the counterfactual scenario of theoretical minimum risk level (TMREL) – the level for a given risk that could minimise population level risk if achieved – we estimated the portion of the burden (deaths and DALYs) that could be attributed to a given risk. We decomposed trends in attributable burden
into contributions from population growth, population age structure, risk exposure, and risk-deleted cause-specific DALY rates. We characterized how risk exposures change as countries  move through the development continuum. GBD 2015 follows the Guidelines for Accurate and Transparent Health Estimates Reporting (GATHER), and provides comprehensive and detailed
information for the data sources, estimation methods, computational tools, and statistical
analysis used to generate estimates of attributable burden.
Between 1990 and 2015, global exposure to unsafe sanitation, household air pollution, childhood underweight, childhood stunting and smoking fell more than 25%. Global exposure for several occupational risks, high body mass index, drug use and ambient air pollution increased more than 25% over the same period. All risks jointly evaluated in 2015 accounted for 58.0% (56.9-59.0%) of global deaths and 41.3% (39.9-42.9%) of DALYs; the largest fraction of  global DALYs was attributable to behavioural (30.3% [28.6-32.0%]). In 2015, the 10 largest Level 3 risks in terms of attributable DALYs at the global level were, in order: high systolic blood pressure (9.3% [8.3-10.3%] of global DALYs), smoking (6.0% [5.3-6.8%]), high fasting plasma glucose (5.8% [5.3-6.4%]), high body-mass index (4.9% [3.5-6.4%]), childhood undernutrition
4.6% [4.1-5.1%]), ambient particular matter (4.2% [3.6-4.8%]), high total cholesterol (3.6% [3- 4.3%]), household air pollution (3.5% [2.6-4.4%]), alcohol use (3.5% [3.1-3.8%]) and diets high in sodium (3.4% [2.0-5.3%]).Decomposition analysis showed that from 1990 to 2015 the number of attributable DALYs declined for micronutrient deficiencies, childhood undernutrition, unsafe
sanitation and unsafe water, and household air pollution but most of these declines were
driven by reductions in risk-deleted DALY rates and not reductions in exposure. For a wide range of risks, increases in attributable burden were driven by population growth and aging exceeding reductions from risk-deleted DALY rates with exposure change having only a minimal contribution. Rising exposure has contributed to notable increases in attributable DALYs from
high body-mass index, high fasting plasma glucose, occupational carcinogens, and drug use. Our
assessments of the relationships between increasing development, measured using the Sociodemographic Index, showed that some environmental risks and childhood undernutrition decline steadily with development while a number of risks like low physical activity, high body-mass index, high fasting plasma glucose, smoking and others increase with development until
the highest quintile. At the country level, metabolic risks such as high BMI and high fasting
plasma glucose increasingly emerged as the leading risk factors for attributable DALYs in 2015.
Nonetheless, regional risk profiles showed sizeable heterogeneity, with smoking still ranked
among the leading five risk factors for attributable DALYs in 140 countries, and childhood
underweight and unsafe sex enduring as primary drivers of early death and disability in much of
sub-Saharan Africa.
Declines in some key environmental risks such as water, sanitation, and household air pollution
have contributed to declines in critical infectious diseases such as diarrhoeal diseases. Many risks
do not appear to change as countries move through the development continuum and have not
played a major role in trends of the last 25 years. Several key risks, including high BMI, high
fasting plasma glucose, drug use, and some occupational exposures, are increasing and
contributing to rising burden from some conditions; nevertheless these risks provide
opportunities for intervention. Some highly preventable risks such as smoking remain major
causes of attributable DALYs even as exposure is declining. Public policy needs to pay careful
attention to the risks that are both major contributors to global burden and are increasing