The Body Mass Index-Mortality Link across the Life Course: Three Selection Biases and Their Effects

• In Event: 546 - Section on Sociology of Population Roundtable Session (one-hour).
  In Refereed Roundtable: Table 06. Mortality

Abstract

Background The effect of obesity on mortality may increase or decrease over the life course, but prior literature has not conclusively determined which is the case. The mixed results may be due to selection biases. In this study, we investigated three selection biases: late entry, mortality selection and healthy participant effects. If these three selection mechanisms are stronger among obese adults than among non-obese adults, they may contribute to a weakening obesity-mortality link over the life course.

Methods We used data from the National Health and Nutrition Examination Survey 1988-2004 with linked mortality files 1988-2006 (n= 22,177 individuals age 25-84.9 years at the time of survey, including 3,820 deaths). We employed weighted Cox models to test and adjust for these three selection biases. We further used Complementary Loglog models adjusted for normal distribution of frailty to test for mortality selection effects; and ordinary least square regression to test for healthy participant effects.

Results Class I obesity is not significantly linked with mortality. Class II/III Obesity-mortality link weakens at older ages adjusted for late entry bias. We did not find evidence for mortality selection and healthy participant effects. Also, even if the healthy participant effects were stronger among obese adults, it would not be strong enough to produce a weakening association between obesity and morbidity for higher ages at the time of the survey.

Conclusions None of these three selection biases are the main mechanisms for the diminishing effect of class II/III obesity on mortality over life course.

Author

• Jonathan Dirlam, The Ohio State University