The Body Mass-Mortality Association in the United States: A Reassessment of Secular Trends

Three recent studies, all using the National Health and Nutrition Examination Surveys (NHANES), reached three different conclusions regarding the changing association between body mass index (BMI) and mortality in the US. This paper used the NHANES I and NHANES III data to examine mortality differences across BMI categories. The purpose is 1) to replicate previous analyses and reconcile discrepant findings in existing research and 2) to focus attention on variations across time periods and birth cohorts as well as variations across socio-demographic sub-populations. Preliminary results show that male and female BMI-related mortality differences are fairly similar in 1971-87, but diverge substantially afterwards. Relative to the normal-weight, mortality for almost all overweight and obese categories increases from 1971-87 to 1988-2006 among women. Relative mortality decreases over time among older men, but the decrease is substantial and significant for the class I obese only. These results caution against sweeping statements about BMI and mortality, and deserve the attention of those interested in the underlying mechanisms of the association and its implications for mortality trends.