Is Income Inequality a Determinant of Population Health? Part 1. A Systematic Review

Abstract

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.

Long-term exposure to income inequality: implications for physical functioning at older ages

“…Previous studies have emphasised the need to adjust for GDP as an indicator of country-level wealth to account for the fact that more unequal countries also tend to be poorer (e.g. Lynch et al 2004). However, in the present sample, the correlation between average inequality and average GDP is actually slightly positive, although non-significant (r = 0.11, p = 0.68).…”

“…It is possible, for example, that cultural and historical factors may lead to a country being both more unequal over time, and more unhealthy, without there being a causal association between inequality and health (Lynch et al 2004). Similarly, other macro-economic factors, not adequately measured by GDP (such as levels of unemployment, social mobility or national spending priorities) might influence both inequality over time and subsequent health.…”

“…This assumption has no basis in the theoretical framework of the inequality hypothesis (see Wilkinson 2005). This may be why previous studies have most strongly supported a detrimental effect of inequality on infant health (Lynch et al 2004;Wilkinson and Pickett 2006), and have been more likely to find an association between inequality and the health of younger people (Dorling et al 2007;LeClere and Soobader 2000), rather than older people who have a longer history of variable exposure to inequality. However, older people are of particular relevance to testing the inequality hypothesis, as, in economically developed countries, they bear the largest burden of disease and mortality.…”

“…Existing research has been neither overwhelmingly supportive nor unsupportive of the inequality hypothesis (Kondo et al 2009;Lynch et al 2004;Wilkinson and Pickett 2006). The majority of this research has been based on examining contemporaneous associations between inequality and health.…”

Recalibrating the spirit level: An analysis of the interaction of income inequality and poverty and its effect on health

“…The stratification scholar is familiar with the principal mediating factors of the relationship, such as race and neighborhood context. Another key finding is the relationship between income inequality and health, which is, however, less robust and more controversial (Beckfield, 2004;Kawachi, Subramanian, & Almeida-Filho, 2002;Kondo et al, 2009;Leigh et al, 2009;Lynch et al, 2004;Mullahy et al, 2008). In the most comprehensive review to my knowledge, Kondo et al (2009) carry out a metaanalysis of 9 cohort studies (59,509,857 subjects) and 19 cross-sectional studies (1,280,211 subjects), suggesting a "modest excess risk of premature mortality and poor self-rated health" (2009, p. 8) associated with income inequality, and the existence of a threshold effect upon which the negative consequences of inequality are remarkably strong (Gini ≥ 0.3).…”