Background: A good understanding of the association between obesity and socioeconomic status (SES) has many important public health and policies implications, particularly for the prevention and management of obesity.

Objective: The objective was to examine secular trends in the relations between overweight (body mass index > or = 95th percentile) and SES.

Design: We examined secular trends in the relation between overweight and SES using nationally representative data collected in the National Health and Nutrition Examination Surveys (NHANES) between 1971 and 2002 for 30 417 US children aged 2-18 y. Poverty income ratio tertiles at each survey were used to indicate low, middle, and high SES.

Results: Considerable race, sex, and age differences were observed in the association between overweight and SES. A reverse association only existed in white girls; African American children with a high SES were at increased risk. Socioeconomic disparities in overweight have changed over time, with an overall trend of weakening. Compared with the medium-SES group, the adjusted odds ratios and 95% CIs were 0.79 (0.47, 1.33), 1.08 (0.73, 1.61), 1.24 (0.73, 2.09), and 1.04 (0.82, 1.33) in NHANES I, II, and III and in the 1999-2002 NHANES for the low-SES group and 0.66 (0.43, 1.00), 0.60 (0.35, 1.03), 0.42 (0.23, 0.76), and 0.99 (0.68, 1.43) for the high-SES group, respectively. Between 1988-1994 and 1999-2002, the ratio in the prevalence of overweight between adolescent boys with a low or high SES decreased from 2.5 to 1.1 and from 3.1 to 1.6 in girls. Consistently across almost all SES groups, the prevalence of overweight was much higher in blacks than in whites.

Conclusions: Complex patterns in the association between SES and overweight exist. Efforts solely targeting reductions in income disparities probably cannot effectively reduce racial disparities in obesity.