NATIONAL BUREAU OF ECONOMIC RESEARCH
NATIONAL BUREAU OF ECONOMIC RESEARCH

Changes in Smoking and Obesity Affect Future Life Expectancy

Life expectancy for 40-year old men in 2040 is expected to increase by 0.92 years compared to... 2010. For women [there is] ... a smaller increase in expected life expectancy -- only 0.26 years.

Deaths from smoking and obesity play a significant role in any estimates of future U.S. life expectancy. Cigarette consumption per adult per year has fallen from a high of more than 4,000 in the early 1960s to fewer than 2,000 in the early 2000s, and that reduction in smoking should increase life expectancy. However, population obesity began to rise in the 1980s, and that trend is associated with decreased life expectancy. To further complicate any estimates of the effects of these trends on mortality, researchers observe that men and women behave differently and thus will be affected differently by changes in smoking and obesity.

In Projecting the Effect of Change in Smoking and Obesity on Future Life Expectancy in the United States (NBER Working Paper No. 18407), co-authors Samuel Preston, Andrew Stokes, Neil Mehta, and Bochen Cao forecast the likely net effect of changes on U.S. mortality rates from 2010 through 2040. They find that men benefit from significantly reduced smoking, with life expectancy for 40-year old men in 2040 expected to increase by 0.92 years compared to life expectancy in 2010. For women, the more muted decline in smoking is largely offset by the surge in obesity, resulting in a smaller increase in expected life expectancy -- only 0.26 years.

The authors note that data from National Health and Nutrition Examination Surveys suggest that the probability of becoming obese, given one's weight at age 25, has been nearly constant for the past 18 years. Given that figure, they estimate that 47 percent of men and 51 percent of women may be obese by 2040. Furthermore, by 2020 and thereafter a majority of obese women will be morbidly obese -- that is, with a body mass index above 35. These changes are expected to raise death rates for 40-to-84 year-old men by as much as 13 percent and for women of the same ages by as much as 20 percent.

Using deaths from smoking-related cancers as a proxy for smoking, the authors estimate that age-specific death rates for male smokers will decline between 2010 and 2040, largely because the heaviest smoking male cohorts were more than 80 years old in 2010. They predict that men will gain 1.5 years of life by 2040 from reduced smoking. Since women began smoking more recently than men, the heaviest smokers among women do not "age out" until 2025-30. Therefore, life expectancy gains for women as a whole rise after 2025, cumulating at 0.85 years for 40-year-old women in 2040.

--Linda Gorman

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