Education, income, and obesity: A nationwide Chinese twin study.

Abstract

This study aimed to examine the association of socioeconomic status with obesity. A total of 39,262 twin individuals were included from the Chinese National Twin Registry (CNTR). Generalized estimating equation models for unmatched twin individual analyses and conditional logistic regression for the co-twin matched design were used. Inference about Causation through Examination of FAmiliaL CONfounding (ICE FALCON) was used to explore the evidence of a causal relationship. In general estimating equation models, high education level and income were associated with lower risk of obesity (odds ratio [OR] = 0.74 [95% CI: 0.65 to 0.84] and 0.86 [95% CI: 0.77 to 0.96]). In conditional logistic regression analysis, the association with education was significant (OR = 0.50 [95% CI: 0.34 to 0.74]) but the association with income was insignificant (OR = 0.74 [95% CI: 0.48 to 1.15]). From the ICE FALCON analysis, a twin's obesity was associated with the co-twin's education and income. After adjusting for the twin's own education, the association disappeared ( <math xmlns="http://www.w3.org/1998/Math/MathML"><msubsup><mi>β</mi> <mrow><mtext>co - twin</mtext></mrow> <mo>'</mo></msubsup> </math>  = -0.10 [95% CI: -0.26 to 0.07]), whereas the twin's obesity was still associated with the co-twin's income but attenuated toward the null ( <math xmlns="http://www.w3.org/1998/Math/MathML"><msubsup><mi>β</mi> <mrow><mtext>co - twin</mtext></mrow> <mo>'</mo></msubsup> </math>  = -0.21 [95% CI: -0.36 to -0.06]). Socioeconomic status is negatively associated with obesity. Education may have a causal effect on obesity, whereas the association between income and obesity is confounded by familial factors.