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Purpose: Simulation models are increasingly being applied to characterize, evaluate and set goals for public health policies. These models seek to integrate secular changes in risk factors for specified birth cohorts to evaluate disease outcomes. Cohort-specific trends may be estimated using longitudinal data, but they are rarely generalizable to the US population. As part of the Cancer Intervention and Surveillance Modeling Network (CISNET), which seeks to decompose past trends in cancer incidence and mortality into underlying changes of lifestyle risk factors, screening, and treatment, we analyzed nationally-representative cross-sectional surveys to provide longitudinal estimates of body mass index (BMI) changes for US adults.
Methods: We compiled 45,343 adult subjects from four National Health and Nutrition Examination Surveys (NHANES I, 1971-1974; NHANES II, 1976-1980; NHANES III 1988-1994; NHANES1999-2002) and adjusted for the sample structure. We fit multivariate generalized estimating equations (GEE) regression models separately for four race and sex groups. Based on the best-fitted models, we calculated cohort-specific average changes in BMI over the period of 1970-2010.
Results: We found significant heterogeneity in weight change patterns by race, sex and birth cohorts. Mean BMI values at age 20 are higher in more recent cohorts and increase more rapidly than earlier cohorts, especially in black women. Based on the model, adults in year 2010 are predicted to be 6-17 kg (14-38 lb) heavier than adults of the same age, race, and sex in 1970. If the trend continues, we predict 33% of white men, 35% of white women, 30% of black men and 51% of black women will be obese in 2010, contrasting the Healthy People 2010 goal of no more than 15% prevalence of obesity in the US. Using these predictions, the CISNET model estimates that approximately 36,000 (1%) colorectal cancer cases and 9,000 (0.6%) colorectal cancer deaths during the period of 1970-2004 were attributable to the secular trends of BMI.
Conclusion: Population-based cross-sectional surveys such as NHANES can provide estimates of average annual changes in BMI as well as other risk factors for specific cohorts in demographic subgroups. These estimates can form the foundation for public health research on evaluating population-wide policies targeting at health behaviors.
See more of Oral Concurrrent Session A - Public Health 1
See more of The 26th Annual Meeting of the Society for Medical Decision Making (October 17-20, 2004)