number of countries, and for a substantial number of countries, data are available for almost no risk factors for the 50-year period examined for this study. Much is known about current international differences in smoking patterns and levels of obesity, but far less about international differences in stress, physical exercise, or social networks.1 Very little is known, moreover, about changes over time and across countries in lifetime exposures and behaviors for most risk factors.

The fluid nature of the relationship between mortality and some of the major risk factors also complicated the panel’s work. For example, the epidemiological literature still reflects considerable differences of opinion with respect to the magnitude of the relationship between obesity and mortality. As the obesity epidemic has spread, the number of people at risk of obesity-related health problems has risen. At the same time, however, management of some of the more serious obesity-related health problems, such as heart disease and type 2 diabetes, has improved. Thus, the net effect of rising obesity on mortality is difficult to estimate.

Acknowledging these limitations, the panel’s strategy was to try to establish the strength of the evidence for a number of the most commonly proffered explanations for differences in life expectancy between the United States and other high-income countries—for example, that these differences are the result of a particularly inefficient U.S. health care system or that they are a function of poor health behaviors in the United States, particularly with respect to smoking, overeating, and failing to exercise sufficiently. The panel also considered differences among countries in levels of social integration and in socioeconomic inequality. Ultimately, all of these potential risk factors will need to be examined in an integrated framework across the entire life course, taking account of the effects of differences in socioeconomic status, behavioral risk factors, and social policy, as well as effects across particular cohorts and periods.

Smoking appears to be responsible for a good deal of the divergence in female life expectancy. Other factors, such as obesity, diet, exercise, and economic inequality, also have likely played a role in explaining the current gap between the United States and other countries, but evidence of their importance to the divergence is not as firm. The case against smoking, by contrast, is quite strong. Fifty years ago, smoking was much more widespread in the United States than in Europe or Japan: a greater proportion of Americans smoked and smoked more intensively than was the case in other


Fortunately, thanks to survey programs such as the Health and Retirement Study in the United States, the English Longitudinal Survey of Ageing in the United Kingdom, and the Survey of Health, Ageing, and Retirement in Europe, large-scale internationally comparable surveys containing important measures of current differences in many variables of relevance now exist. Nevertheless, the empirical basis for certain conclusions is significantly stronger in some cases than in others.

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