Birth cohort effects among U.S.-born adults born in the 1980s: Foreshadowing future trends in U.S. obesity prevalence

BACKGROUND: Obesity prevalence stabilized in the U.S. in the first decade of the 2000s. However, obesity prevalence may resume increasing if younger generations are more sensitive to the obesogenic environment than older generations. METHODS: We estimated cohort effects for obesity prevalence among young adults born in the 1980s. Using data collected from the National Health and Nutrition Examination Survey between 1971 and 2008, we calculated obesity for respondents aged between 2 and 74 years. We used the median polish approach to estimate smoothed age and period trends; residual non-linear deviations from age and period trends were regressed on cohort indicator variables to estimate birth cohort effects. RESULTS: After taking into account age effects and ubiquitous secular changes, cohorts born in the 1980s had increased propensity to obesity versus those born in the late 1960s. The cohort effects were 1.18 [95% CI: 1.01, 1.07] and 1.21 [95% CI: 1.02, 1.09] for the 1979–1983 and 1984–1988 birth cohorts, respectively. The effects were especially pronounced in Black males and females but appeared absent in White males. CONCLUSIONS: Our results indicate a generational divergence of obesity prevalence. Even if age-specific obesity prevalence stabilizes in those born before the 1980s, age-specific prevalence may continue to rise in the 1980s cohorts, culminating in record high obesity prevalence as this generation enters its ages of peak obesity prevalence.