United States fares poorly on life expectancy relative to other 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 changing 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 the current gap and divergence between the United States and other countries. 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 countries. The health consequences of this behavior are still playing out in today’s mortality rates. Over the period 1950–2003, the gain in life expectancy at age 50 was 2.1 years lower among U.S. women compared with the average of nine other high-income countries (5.7 vs. 7.8 years gained, respectively). The damage caused by smoking was estimated to account for 78 percent of the gap in life expectancy for women and 41 percent of the gap for men between the United States and other high-income countries in 2003. Smoking also has caused significant reductions in life expectancy in the Netherlands and Denmark, which as noted are two other countries with relatively poor life expectancy trends.

Other factors, particularly the rising level of obesity in the United States, also appear to have played a significant part, although as noted, there is still a good deal of uncertainty in the literature regarding the mortality consequences of obesity and possible trends therein. Obesity may account for a fifth to a third of the shortfall of life expectancy in the United States relative to the other countries studied. Other specific risk factors also are surely important, but their effects are even more difficult to quantify. The panel found some evidence to suggest that adults aged 50 and over in the United States are somewhat more sedentary than those in Europe, but the research base is insufficient even to identify a reasonable range of uncertainty in estimates of the contribution of physical activity to international differences or trends in mortality.

In other cases, the panel determined that certain risk factors are unlikely to have played a major role in the divergence of life expectancy in various countries over the past 25 years. A large body of work shows a causal relationship between social ties and social integration and mortality. Yet there



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