Obesity Prevalence in United States Linked To Significant Increase Over 4 Decades

Although the period of emerging adulthood, from ages 18 - 25 years, is considered a distinct developmental period leading to the formation of lifelong habits and identity, the lack of studies describing obesity prevalence in this patient population has limited opportunity for developmentally informed intervention and treatment.

Led by Alejandra Ellison-Barnes, MD, Johns Hopkins University School of Medicine, a team of investigators examined changes in obesity prevalence nationally among emerging adults in the United States, finding its prevalence among emerging adults in the US increased significantly from 1976 - 2018.

Methods

Ellison-Barnes and colleagues used national, representative data from the National Health and Nutrition Examination Survey (NHANES). The NHANES encompassed a series of cross-sectional studies that included interviews and physical examinations, with a stratified, multistage sampling design.

From this, the team drew data from the NHANES II (1976 - 1980), NHANES III (1988 - 1994), and the continuous NHANES cycles from 1999 through 2018, with a response rate range of 48.8% - 80%.

The study population was limited to non-pregnant, emerging adults (18 - 25 years) of non-Hispanic Black or non-Hispanic White race with complete data for variables of interest (89.8% of population).

According to the team, the defined outcomes of interest included body mass index (BMI) , categorized into underweight (< 18.5), normal weight (18.5 - 24.9), overweight (25 - 29.9), and obesity (≥ 30).

Investigators included covariates such as sex, race and ethnicity, and household poverty, but they did not include age. An estimated mean BMI and prevalence of each BMI group with 95% confidence intervals were calculated using NHANES examination weights to account for complex sampling design and adjust for all covariates.

Findings

A total of 8015 emerging adults were included, consisting of 3965 female patients, 3037 non-Hispanic Black, and 2386 who met criteria for household poverty.

Throughout the 4 decade period, the mean BMI increased from 23.1 (95% CI, 22.9 - 23.4) in 1976 - 1980, to 27.7 (95% CI, 26.2 - 29.1) in 2017 - 2018, at P = .006 for trend using a nonparametric test).

Then, between 1976 - 1980 and 2017 - 2018, the prevalence of obesity increased from 6.2% (95% CI, 4.9% - 7.9%) to 32.7% (95% CI, 24.7% - 41.8%, P = .007 for trend using a nonparametric test).

On the other hand, normal weight was shown to have decreased from 68.7% (95% CI, 66.3% - 70.9%) to 37.5% (95% CI, 29.5% - 46.4%, P = .005 for trend using a nonparametric test).

Lastly, the investigators remarked on the demographic limitations of the study, limited to non-Hispanic Black and non-Hispanic White individuals, which may not be able to be generalized to other races or ethnicities.

Takeaways

Ellison-Barnes and colleagues noted the urgent need for research on risk factors contributing to obesity during the developmental stage, in order to define the design of interventions and policies aimed at prevention.

“Emerging adulthood may be a key period for preventing and treating obesity given that habits formed during this period often persist through the remainder of the life course,” they wrote.

The research letter, “Trends in Obesity Prevalence Among Adults Aged 18 Through 25 Years, 1976-2018,” was published in JAMA.