Foreman KJ, et al. - Considering the significance of understanding potential trajectories in health and drivers of health to guiding long-term investments and policy implementation, researchers provided a novel approach to modelling life expectancy, all-cause mortality and cause of death forecasts—and alternative future scenarios—for 250 causes of death from 2016-2040 in 195 countries and territories. As per reference forecast, overall improvements are expected through 2040 in most countries. However, in the absence of deliberate policy action, the range found across better and worse health scenarios may provide a precarious vision of the future—a world with accelerating progress from technical innovation but with the potential for worsening health outcomes.

Methods

• Researchers generated predictions for 2017–2040 via modeling 250 causes and cause groups organized by the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) hierarchical cause structure, using GBD 2016 estimates from 1990–2016.
• Data from the GBD 2016 study was used for the modeling framework to systematically account for the relationships between risk factors and health outcomes for 79 independent drivers of health.
• A three-component model of cause-specific mortality was developed: a component due to changes in risk factors and select interventions; the underlying mortality rate for each cause that is a function of income per capita, educational attainment, and total fertility rate under 25 years and time; and an autoregressive integrated moving average model for unexplained changes correlated with time.
• The performance was determined via fitting models with data from 1990–2006 and using these to forecast for 2007–2016.
• They fitted the final model used for generating forecasts and alternative scenarios to data from 1990–2016.
• For 195 countries and territories, this model was used to generate a reference scenario or forecast through 2040 for each measure by location.
• Additionally, based on the 85th and 15th percentiles, they generated better health and worse health scenarios, respectively, of annualized rates of change across location-years for all the GBD risk factors, income per person, educational attainment, select intervention coverage, and total fertility rate under 25 years in the past.
• All-cause age-sex specific mortality, life expectancy, and years of life lost (YLLs) for 250 causes were generated using the model.
• In a cohort component model, scenarios for fertility were also generated and used to generate population scenarios.
• Estimates of mortality and YLLs attributable to each risk factor in the future were generated for each reference forecast, better health, and worse health scenarios.

Results

• Globally, improvement in most independent drivers of health is expected by 2040, but 36 were forecast to worsen.
• The better health scenarios suggest a possibility of greater progress, but some drivers such as high body-mass index (BMI) will rise in the absence of intervention.
• Increase in global life expectancy by 4·4 years (95% UI 2.2 to 6.4) for men and 4.4 years (2.1-6.4) for women by 2040 is forecast; however, better and worse health scenarios indicate that trajectories could range from a gain of 7.8 years (5.9-9.8) to a non-significant loss of 0.4 years (–2.8 to 2.2) for men, and an increase of 7.2 years (5.3- 9.1) to essentially no change (0.1 years [–2.7 to 2.5]) for women.
• Japan, Singapore, Spain, and Switzerland displayed a forecasted life expectancy exceeding 85 years for both sexes, and 59 countries including China were projected to surpass a life expectancy of 80 years by 2040.
• At the same time, life expectancies below 65 years is projected for Central African Republic, Lesotho, Somalia, and Zimbabwe by 2040, indicating persistence of likelihood of global disparities in survival if current trends hold.
• Population growth and ageing partly influence the forecasted YLLs indicating a rising toll from several non-communicable diseases (NCDs).
• For HIV/AIDS, most striking differences between the reference forecast and alternative scenarios were noted, for this a potential increase of 120.2% (95% UI 67.2–190.3) in YLLs (nearly 118 million) was projected globally from 2016–2040 under the worse health scenario.
• Compared with 2016, by 2040, NCDs were forecasted to account for a greater proportion of YLLs in all GBD regions (67.3% of YLLs [95% UI 61.9–72.3] globally); nevertheless, communicable, maternal, neonatal, and nutritional (CMNN) diseases still accounted for a large share of YLLs in many lower-income countries in 2040 (eg, 53.5% of YLLs [95% UI 48.3–58.5] in Sub-Saharan Africa).
• For many health risks, large gaps were noted between the reference forecast and better health scenario for attributable YLLs.
• Some of the largest differences between reference and better health scenarios were evident for metabolic risks amenable to health care (eg, high blood pressure and high plasma fasting glucose) and risks best targeted by population-level or intersectoral interventions (eg, tobacco, high BMI, and ambient particulate matter pollution) in most countries.
• Sub-Saharan Africa was the main exception, where substantive disparities between reference and better health scenarios in 2040 were forecasted, which were attributable to many risks correlated with poverty and lower levels of development (eg, unsafe water and sanitation, household air pollution, and child malnutrition).