Lynch, John W., G.D. Smith, S. Harper, Marianne M. Hillemeier, N. Ross, George A. Kaplan, and M. Wolfson. 2004. "Is Income Inequality a Determinant of Population Health? Part 1. A Systematic Review." Milbank Quarterly, 82(1): 5-99.
This article reviews 98 aggregate and multilevel studies examining the associations between income inequality and health. Overall, there seems to be little support for the idea that income inequality is a major, generalizable determinant of population health differences within or between rich countries. Income inequality may, however, directly influence some health outcomes, such as homicide in some contexts. The strongest evidence for direct health effects is among states in the United States, but even that is somewhat mixed. Despite little support for a direct effect of income inequality on health per se, reducing income inequality by raising the incomes of the most disadvantaged will improve their health, help reduce health inequalities, and generally improve population health.