Since life expectancy at age 50 in the United States would increase significantly more than in other countries through the hypothetical elimination of obesity, the U.S. longevity shortfall would be reduced and in some cases eliminated. U.S. life expectancy for women is 1.37 years lower than the mean in 12 other countries with higher life expectancies. Based on the PSC risk factors, U.S. female life expectancy would be an estimated 0.80 years lower than this mean without obesity, so that obesity would account for an average of 41 percent of the gap. For men, the equivalent percentage of the difference in life expectancy accounted for by obesity, relative to 10 countries with higher life expectancies, is 67 percent.
These effects are much larger than those based on the Adams et al. or Mehta and Chang risk sets. The mean life expectancy gap for the 12 countries with higher life expectancies is reduced by 29 percent for women using Adams’ risks to account for the effects of obesity and by 22 percent using Mehta and Chang’s. For men, the equivalent reductions are 32 percent and 29 percent respectively.
Thus, differences in the prevalence of obesity continue to explain about 20–35 percent of the shortfall in U.S. life expectancy relative to countries with superior levels, even when one uses much lower sets of obesity risks. The risks derived from the studies of Adams and colleagues (2006) and Mehta and Chang (2010) have the advantage of pertaining to a later period, on average, than those of the PSC. This period is closer to the time when the levels of both obesity and mortality are recorded in the various countries and when attributable risks are modeled. These studies also control for socioeconomic status, indexed by education and income, in their analyses of the impact of obesity on mortality, unlike the analysis based on risks in the PSC. Using data from the Health and Retirement Study, Mehta and Chang (2009) show that controlling for educational attainment reduces estimated obesity risks by 20–50 percent. The panel is inclined to believe that the two sets of relative risks recorded more recently in the United States yield more reliable estimates of the impact of obesity on life expectancy comparisons than those obtained using the PSC risks. Even using the sets of lower obesity risks, however, it appears that differences in obesity account for a fifth to a third of the shortfall in life expectancy in the United States relative to other countries. Obesity appears to be an important part of the explanation of the current U.S. shortfall in life expectancy, but uncertainty remains as to its role in explaining the divergence.