Income Inequality Among American States and the Risk for Coronary Heart Disease

INTRODUCTION:  Heart attack is the number one leading cause of death in the United States. Individual characteristics (i.e. socioeconomic status), behaviors (i.e. smoking, physical activity, and diet), and other health conditions (i.e. weight status and hypertension), have been identified as significant risk factors for Coronary Heart Disease (CHD). According to the Social Determinants of Health Framework, characteristics of the social and economic environment, such as income inequality, play a role in population health.  However, studies utilizing cohort data is lacking. Therefore, the objective of this investigation was to determine the longitudinal association between income inequality and CHD risk factors and health outcomes.

METHODS:  We used data from the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC) longitudinal study (n=43 093).  Respondents completed structured diagnostic interviews at baseline (2001-2002) and follow-up (2004-2005).  Weighted multilevel modeling was used to determine if US state-level income inequality (measured by the Gini coefficient) was a predictor of CHD at baseline and at follow-up, while controlling for individual-level and state-level covariates. We also created a propensity score for Heart Attack using demographic, behavioral and health status variables. The relationship between income inequality and the propensity score was then determined. 

RESULTS:  At baseline, state-level inequality was associated with increased risk for overweight status and smoking behavior.  In comparison to respondents living in the lowest quartile of income inequality (the most equal), those living in the second (OR=1.71, 95% CI 1.14 to 2.57), third (OR=1.85, 95% CI 1.27 to 2.89), and fourth (OR=2.09, 95% CI 1.26 to 2.45) quartiles were significantly more likely to experience a heart attack during follow-up.  Similar findings were obtained when those who previously had a heart attack at or before baseline were excluded.  Also, income inequality was associated with the propensity score for heart attack. 

CONCLUSIONS:  Living in a state with higher income inequality increases the risk for CHD among US adults.