Income disparity and risk of death: the importance of health behaviors and other mediating factors

Abstract

Background: Income disparities in mortality are profound in the United States, but reasons for this remain largely unexplained. The objective of this study was to assess the effects of health behaviors, and other mediating pathways, separately and simultaneously, including health insurance, health status, and inflammation, in the association between income and mortality.

Methods: This study used data from 9925 individuals aged 20 years or older who participated in the 1999-2004 National Health and Nutrition Examination Survey (NHANES) and were followed up through December 31, 2006 for mortality. The outcome measures were all-cause and CVD/diabetes mortality. During follow-up 505 persons died, including 196 deaths due to CVD or diabetes.

Results: After adjusting for age, sex, education, and race/ethnicity, risk of death was higher in low-income than high-income group for both all-cause mortality (Hazard ratio [HR], 1.98; 95% confidence interval [CI]: 1.37, 2.85) and cardiovascular disease (CVD)/diabetes mortality (HR, 3.68; 95% CI: 1.64, 8.27). The combination of the four pathways attenuated 58% of the association between income and all-cause mortality and 35% of that of CVD/diabetes mortality. Health behaviors attenuated the risk of all-cause and CVD/diabetes mortality by 30% and 21%, respectively, in the low-income group. Health status attenuated 39% of all-cause mortality and 18% of CVD/diabetes mortality, whereas, health insurance and inflammation accounted for only a small portion of the income-associated mortality (≤6%).

Conclusion: Excess mortality associated with lower income can be largely accounted for by poor health status and unhealthy behaviors. Future studies should address behavioral modification, as well as possible strategies to improve health status in low-income people.

Figure 1. Schematic Diagram of Some Pathways That Mediate the Association Between Income and Mortality.

Mediating effect was Calculated as: (β _{Model I –} β _{Model I+mediator(s)}) × 100/β _{Model I} for all-cause mortality (β _{Model II -} β _{Model II+mediator(s)}) × 100/β _{Model II} for CVD/diabetes mortality.

Figure 2. Overlap Between Health Behaviors and Health Status.

Example of calculation for all-cause mortality, low-income group: Mediating effect of Health Behaviors and Health Status = 57% Mediating effect of Health Behaviors = 30%; Mediating effect of Health Status = 39% Combined effect = 30%+39% = 69% Overlap = 69% –57% = 12% Health Behaviors, independent Effect = 30%–12% = 18% Health Status, Independent Effect = 39%–12% = 27%.