Cohort-based income gradients in obesity among U.S. adults

United States Long-Term Trends in Adult BMI (1959-2018): Unraveling the Roots of the Obesity Epidemic

The escalating rates of obesity since the 1950s poses a critical public health challenge across all age groups in the United States. While numerous studies have examined cross-sectional disparities across racial, ethnic, and socioeconomic groups, there has been limited research on long-term trends. To address this gap, we analyzed average adult body mass index (BMI) trends from 1959 to 2018, using data from the National Health and Nutrition Examination Survey (NHANES) and the National Health Examination Survey (NHES). Employing time series analysis, we evaluated BMI trends across income, education, and race/ethnicity. The results revealed a consistent upward trajectory in average BMI across all groups over the six-decade period, with no significant differences by income or education levels among high school graduates. However, individuals with less than a high school education displayed a more gradual increase in BMI. Racial disparities were also evident, with Black adults showing higher BMI growth rates compared to White adults, while Hispanic and other racial groups experienced slower increases. These findings underscore the need for systemic interventions to address the ongoing obesity epidemic, emphasizing the importance of research to identify trends over time and a system-thinking approach to inform effective population-level interventions and policy decisions.

Are there birth cohort effects in disparities in child obesity by maternal education?

BACKGROUND

Children belonging to the same birth cohort (i.e., born in the same year) experience shared exposure to a common obesity-related milieu during the critical early years of development-e.g., secular beliefs and feeding practices, adverse chemical exposures, food access and nutrition assistance policies-that set the stage for a shared trajectory of obesity as they mature. Fundamental cause theory suggests that inequitable distribution of recent efforts to stem the rise in child obesity may exacerbate cohort-based disparities over time.

METHODS

Data were from electronic health records spanning 2007-2016 linked to birth records for children ages 2-19 years. We used hierarchical age-period-cohort models to investigate cohort effects on disparities in obesity related to maternal education. We hypothesized that maternal education-based disparities in prevalence of obesity would be larger among more recent birth cohorts.

RESULTS

Sex-stratified models adjusted for race/ethnicity showed substantial obesity disparities by maternal education that were evident even at young ages: prevalence among children with maternal education < high school compared to maternal college degree was approximately three times as high among girls and twice as high among boys. For maternal education < high school, disparities compared to maternal college degree were higher in more recent birth cohorts. Among girls, this disparity cohort effect was evident at younger ages (at age 4, the disparity increased by 4 [0.1-8] percentage points per 5 birth years), while among boys it was larger at older ages (at age 16, the disparity increased by 7 [1-14] percentage points per 5 birth years).

CONCLUSIONS

There may be widening maternal education-based disparities in child obesity by birth cohort at some ages.