Background: The theory that income inequality and characteristics of the psychosocial environment (indexed by such things as social capital and sense of control over life's circumstances) are key determinants of health and could account for health differences between countries has become influential in health inequalities research and for population health policy.
Methods: We examined cross-sectional associations between income inequality and low birthweight, life expectancy, self-rated health, and age-specific and cause-specific mortality among countries providing data in wave III (around 1989-92) of the Luxembourg Income Study. We also used data from the 1990-91 wave of the World Values Survey (WVS). We obtained life expectancy, mortality, and low birthweight data from the WHO Statistical Information System.
Findings: Among the countries studied, higher income inequality was strongly associated with greater infant mortality (r=0.69, p=0.004 for women; r=0.74, p=0.002 for men). Associations between income inequality and mortality declined with age at death, and then reversed among those aged 65 years and older. Income inequality was inconsistently associated with specific causes of death and was not associated with coronary heart disease (CHD), breast or prostate cancer, cirrhosis, or diabetes mortality. Countries that had greater trade union membership and political representation by women had better child mortality profiles. Differences between countries in levels of social capital showed generally weak and somewhat inconsistent associations with cause-specific and age-specific mortality.
Interpretation: Income inequality and characteristics of the psychosocial environment like trust, control, and organisational membership do not seem to be key factors in understanding health differences between these wealthy countries. The associations that do exist are largely limited to child health outcomes and cirrhosis. Explanations for between-country differences in health will require an appreciation of the complex interactions of history, culture, politics, economics, and the status of women and ethnic minorities.