Background: Understanding the natural history of obesity in a population may be a critical step toward developing effective interventions.
Objective: To assess the development of body mass and examine the role of race or ethnicity, sex, and birth year in obesity onset in young U.S. adults.
Design: Prospective cohort study.
Setting: The National Longitudinal Survey of Youth 1979, a national sample with oversampling of minority ethnic groups.
Participants: 9179 persons.
Measurements: Body mass index (BMI) calculated from 12 self-reported height and weight samples recorded between 1981 and 1998. Logistic regression identified predictors of obesity at age 35 to 37 years. Cox proportional hazards models compared the incidence of obesity by ethnicity and birth year.
Results: Overall, 26% of men and 28% of women were obese (BMI > or = 30 kg/m2) by age 35 to 37 years. Race or ethnicity and baseline BMI were significant predictors of obesity. Obesity onset was 2.1 (95% CI, 1.6 to 2.7) times faster for black women and 1.5 (CI, 1.1 to 2.0) times faster for Hispanic women than for white women. The pattern for men differed: Overall, obesity developed most rapidly in Hispanic men, but relative rates of obesity onset for white men compared with black men varied according to age. The rate of obesity onset increased 26% to 28% over an 8-year span in birth year.
Conclusions: Marked ethnic-based differences were found in rates of weight accumulation in young U.S. adults, with later birth cohorts experiencing earlier onset of obesity. To alter the course of obesity in the United States, interventions should target young adults, especially those of minority ethnic groups.