Beefing up with the Chans: evidence for the effects of relative income and income inequality on health from the China Health and Nutrition Survey

A great deal of research has examined the hypothesis that the well-being of individuals is shaped not just by the absolute level of resources available to them but also the level of resources available to them relative to others in their cohort or community. Several causal pathways have been hypothesized to explain associations between relative social position and health. For example, greater community income could increase the overall availability of health care in a community or decrease the availability for people for any given level of individual income. Relative social position could also create stress, resulting in adverse health outcomes through increased hypertension and other pathways. We explore yet another pathway by which relative social position may affect health. Specifically, to the extent that norms about physical appearance might be shaped by one's observations of others, we examine whether obesity might constitute another physiologic pathway by which community attributes could influence aspects of individual health, such as hypertension. We examine this hypothesis in rural China, where income often limits food intake so that, if community norms are an important determinant of individual obesity, higher community income could increase the obesity rate in a community and therefore change norms about obesity. These norms, in turn, could increase individuals' chances of being obese given their income. To test this hypothesis, we use multilevel linear probability models to examine the relationship between ecologic factors, i.e., relative income and income inequality, and health risk factors, i.e., obesity and hypertension among a sample of Chinese adults interviewed in four waves over 9 years. The results suggest that, among rural Chinese residents, increasing community average income and income inequality are positively associated with both obesity and hypertension. However, the effect of relative income on hypertension is not accounted for by increases in obesity. We did not find a strong relationship between socioeconomic conditions and the health risk factors among urban residents, where norms might be likely to be less strongly influenced by local attributes. Hence, the present study provides evidence supporting the hypothesis that relative income and income inequality affect obesity and hypertension, but no evidence that the effects on hypertension operated through effects on obesity.