Life expectancy, the average number of years people can expect to live, is an important summary measure of health. Forecasting how life expectancy will develop in the future is essential for public policy, social security and healthcare planning. Most mortality forecasts, however, rely purely on the extrapolation of past age-specific mortality trends, which could easily result in unreliable outcomes because lifestyle factors such as smoking, alcohol and obesity – which can lead to temporal fluctuations in mortality trends – are ignored.
In their study, Fanny Janssen (Netherlands Interdisciplinary Demographic Institute (NIDI) and University of Groningen (UoG)) and colleagues introduce a novel mortality forecasting technique that takes into account both the impact of smoking, obesity and alcohol on mortality trends and the mortality experience of forerunner populations.
Their approach to mortality forecasting relied on an analysis of past mortality trends and their determinants. In line with the evidence gathered, they distinguished between (1) the general and gradual long-term decline in mortality not affected by smoking, obesity and alcohol (= non-lifestyle-attributable mortality) that they extrapolated into the future, while taking into account the mortality experiences of other countries; and (2) deviations from and differences in this general mortality decline caused predominantly by the time-varying impact of smoking, obesity and alcohol on mortality, which they projected separately using more advanced projection techniques.
The authors project that life expectancy at birth, in the 18 European countries studied, will increase from, on average, 83.4 years for women and 78.3 years for men in 2014 to 92.8 years for women and 90.5 years for men in 2065. Compared to a benchmark Lee-Carter mortality extrapolation and the 2020 mortality forecasts by Eurostat and the United Nations, the projection results in higher future life expectancy values, more realistic differences in future life expectancy between countries and between sexes and additional insights into what is driving future life expectancy values. More specifically, compared to the Lee-Carter age-period mortality extrapolation, the projection by Janssen et al. results, on average, in 2.6 years higher life expectancy at birth (e0) in 2065 for men, and 2.2 years higher for women; in smaller differences in future e0 between countries and sexes; and in non-linear future increases in e0, in line with the shift towards the higher e0 values for non-lifestyle-attributable mortality. Compared to the 2020 official mortality forecasts by Eurostat and the United Nations (2020), the projection by Janssen et al. resulted in projected e0 values in 2065 that were 5 years higher for men, and 3 to 4 years higher for women.
Their findings of (1) higher projected life expectancy values than those currently obtained and (2) of a rather steady long-term increase in life expectancy after the effects of smoking, obesity and alcohol are controlled for, imply longer individual lifespans, and more older people in society than previously anticipated, but also that a limit to human life expectancy is not within reach.
The novel approach, which distinguishes between the underlying long-term mortality decline and the remaining factors that cause deviations from this mortality decline, could be adopted as well to account for the impact of the COVID-19 pandemic on mortality and life expectancy.
Funding: The publication comprises the concluding article of the research project by Fanny Janssen entitled ‘Smoking, alcohol, and obesity, ingredients for improved and robust mortality projections’ (see www.futuremortality.com) funded by the Netherlands Organisation for Scientific Research (NWO) (grant no. 452-13-001).