The natural history of the development of obesity in a cohort of young U.S. adults between 1981 and 1998.

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.