In Explaining Divergent Levels of Longevity in High-Income Countries, a new report from the National Research Council, the researchers cite historical heavy smoking as a major reason why lifespans in the U.S. still fall short of those in many other high-income nations - over the last 25 years, life expectancy at age 50 in the U.S. has been rising, but at a slower pace than in many other high-income countries, such as Japan and Australia.
The reason, the study notes, is that three to five decades ago, smoking was much more widespread in the U.S. than in Europe or Japan - the opposite of the situation now - but they say the health consequences are still playing out in today’s mortality rates. They also say smoking also has significantly reduced life expectancy in Denmark and the Netherlands, two other countries with lower life expectancy trends than comparable high-income countries.
They correlate a lag of two to three decades between smoking and its peak effects on mortality, so they predict life expectancy for men in the U.S. is likely to improve relatively rapidly in coming decades because of reductions in smoking in the last 20 years, the report says. For U.S. women, whose smoking behavior peaked later than men’s, declines in mortality are apt to remain slow for the next decade. Similarly, life expectancy in Japan is expected to improve less rapidly than it otherwise would, because of more-recent high smoking rates.
Increases in obesity’s also appear to be significant, the report says. While there is still uncertainty in the literature about the magnitude of the relationship between obesity and mortality, they don't hesitate to say it may account for a fifth to a third of the shortfall in longevity in the U.S. compared to other nations. So, if the obesity trend in the U.S. continues, it may offset the longevity improvements expected from reductions in smoking. However, recent data suggest that the prevalence of obesity in the U.S. has leveled off, and some studies indicate that the mortality risk associated with obesity has declined.
While nationalized health care is all the rage in the U.S., those who need it most - the elderly - will get no benefit from it, since they have access to Medicare already and cancer detection and survival appear to be better in the U.S. than in most other high-income nations. Survival rates following a heart attack also are favorable.
Disputing some recent work that suggests important connections between the strength of social ties and mortality, the committee that wrote the report found little compelling data to indicate that differences in social networks among people in high-income countries are related to the differing patterns of life expectancy. Similarly, little evidence supports the hypothesis that hormone therapy has played a part in the relatively lower longevity for American women.
The study committee also identified many gaps in research. While lung cancer deaths are a reliable marker of the damage from smoking, no clear-cut marker exists for obesity, physical inactivity, social integration, or other risks considered in this report. Moreover, evaluation of these risk factors is based on observational studies, which -- unlike randomized controlled trials -- are subject to many biases. While there is no perfect substitute for randomized controlled trials, studies that take advantage of natural experiments, such as increased cigarette taxes or a dramatic change in the use of hormone therapy, can sometimes serve as valuable supplements to them.
The report was sponsored by the National Institute on Aging’s Division of Behavioral and Social Research.
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