U.S. Life Expectancy: Impact of Smoking and Obesity

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If current obesity trends continue, life expectancy gains due to decreases in smoking could potentially be canceled out in the future, according to research published this week in the New England Journal of Medicine. By analyzing data from several national health surveys including tens of thousands of respondents, researchers Susan Stewart, David Cutler and Dr. Allison Rosen were able to forecast future life expectancy trends—both incorporating major changes in lifestyle and smoking, and projecting how current obesity trends might impact life expectancy if allowed to continue on the current trajectory. If all U.S. adults became nonsmokers of normal body weight by 2020, nationwide life expectancy could increase by 3.76 years, they say. Yet, if current obesity trends continue, roughly a quarter of that gain—or some 9 months of life expectancy—would be lost. In other words, the researchers write:

“If past obesity trends continue unchecked, the negative effects on the health of the U.S. population will increasingly outweigh the positive effects gained from declining smoking rates. Failure to address continued increases in obesity could result in an erosion of the pattern of steady gains in health observed since early in the 20th century.”

Projecting possible life expectancy based on a nation of total non-smokers who aren’t obese or overweight is unrealistic, the researchers concede, but it helps illustrate the point of how sizable a public health toll these factors take. If long-term smoking trends persist—with a general decrease of 1.5% per year—researchers suggest that by 2020 the population of current smokers will drop by 21%, the population of former smokers who have quit in the previous 10 years will drop by 44%, and those who have had a smoke-free decade or more will increase by 5%.

All of that should be great news for public health, but when those projections are put alongside figures for obesity rates, the picture is less promising. If current obesity trends continue, by 2020, nearly half of the U.S. population (45%) will be classified as obese, according to World Health Organization standards. That means that, while fewer people may experience the negative health effects of smoking, at the same time more will experience the increased risks for heart disease, diabetes and other health complications associated with obesity.

Of course, however detailed, this analysis cannot incorporate every single contributing factor, and researchers point out that the results were not broken down by race or ethnicity, which could impact life expectancy predictions—as average body mass index has grown more quickly in certain ethnic groups. Additionally, though researchers factored in the impact of medical advancements on longevity, the model was based on historic trends and may not keep pace with the influence of medical breakthroughs in the future. All of that said, however, the underlying message is nonetheless clear—and it is one that has been echoing through the medical community for years. As the researchers conclude:

“[T]he detrimental effect of increases in obesity rates on population health is tempered only somewhat by the decline in the prevalence of smoking. Efforts to improve health should focus on stabilization or reversal of trends in BMI, continued reductions in tobacco use, and better control of the clinical risk factors associated with obesity and smoking.”

And if we don’t manage to address these major health concerns—and curb our collective bad habits—we run the risk of slowing the steady health improvements of the last century.