Trends in the association between obesity and socioeconomic status in U.S. adults: 1971 to 2000.
OBJECTIVE
To study the secular trends in the disparity of obesity across socioeconomic status (SES) groups among U.S. adults.


METHODS
We used national representative data collected in the National Health and Nutrition Examination Surveys conducted in 1971 to 1974, 1976 to 1980, 1988 to 1994, and 1999 to 2000 from 28,543 adults 20 to 60 years old. Obesity was defined based on BMI calculated using measured weight and height. Trends in the relationship between obesity and education levels were analyzed controlling for age, gender, and ethnicity.


RESULTS
The disparity in obesity across SES (less than high school, high school, and college or above to indicate low, medium, and high SES, respectively) has decreased over the past 3 decades. In National Health and Nutrition Examination Surveys I (1971 to 1974), there was as much as a 50% relative difference in the obesity prevalence across the three groups, but by 1999 to 2000, it decreased to 14%. This trend was more pronounced in women. The trends of diminishing disparities in obesity were also revealed by our logistic and linear regression analyses. The odds ratio converged to 1 from the 1970s to 2000. In most sociodemographic groups, the relationship between BMI and SES (coefficients) has been weakened over time.


CONCLUSIONS
The association between SES and obesity has been weakened over the past 3 decades, when the prevalence of obesity increased dramatically. There are considerable variations in the changes in the associations across gender and ethnic groups. Our findings suggest that individual characteristics are not likely the main cause of the current obesity epidemic in the U.S., whereas social-environmental factors play an important role. Strategies for obesity prevention and management should target all SES groups from a societal perspective.
Zhang
Qi
Q
Section of General Internal Medicine, University of Chicago, 5841 South Maryland Avenue, MC 2007, Chicago, IL 60637, USA. qzhang@medicine.bsd.uchicago.edu
Wang
Youfa
Y
D000328:Adult; D015992:Body Mass Index; D004522:Educational Status; D005260:Female; D006801:Humans; D016014:Linear Models; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D009749:Nutrition Surveys; D009765:Obesity / Q000453:epidemiology*; D016017:Odds Ratio; D015995:Prevalence; D012923:Social Class; D014481:United States / Q000453:epidemiology