Regional differences in intercohort and intracohort trends in obesity in the USA: evidence from the National Health Interview Survey, 1982-2018

Objectives Obesity in the USA is more prevalent in younger cohorts than older cohorts and also more prevalent in the South and the Midwest than other regions. However, little research has examined the intersection of cohort patterns and regional differences in obesity. We address the knowledge gap by investigating net of age and period trends, how intercohort and intracohort patterns in obesity may depend on Census regions for black and white men and women. Design, setting and participants A total of 1 020 412 non-Hispanic black and white respondents aged 20-69 were included from the 1982-2018 National Health Interview Survey. Outcome measures Obesity is defined as body mass index ≥30 kg/m 2 based on participant self-reported weight and height. Obesity ORs were calculated to estimate region-specific age, period and cohort patterns for each demographic group. Results Although age and period trends in obesity were similar across regions for all demographic groups, cohort patterns depended on region of residence for white women. Specifically, for the white women cohorts born in 1955 or later, living in the South and the Midwest implied higher likelihood of obesity than their peers in other regions even after accounting for average regional differences. These cohorts' disadvantage seemed to persist and/or accumulate over the life course. Socioeconomic factors explained little average regional differences or region-specific cohort variation. Conclusions Our findings highlight the interdependence of the temporal and geographical processes in shaping obesity disparities.