Income inequality, the psychosocial environment, and health: comparisons of wealthy nations

doi:10.1016/S0140-6736(01)05407-1

The Lancet

Volume 358, Issue 9277, 21 July 2001, Pages 194-200

https://doi.org/10.1016/S0140-6736(01)05407-1 Get rights and content

Summary

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.

Introduction

There has been great interest in understanding links between income inequality and health.1, 2, 3, 4 Some studies have examined income inequality in relation to between-country health differences,5, 6 while others have analysed associations of income inequality and health within countries.7, 8 Two distinct questions have been raised. First, for a given average income, is the extent of inequality in the distribution of income associated with differences in average population health between countries or between regions (eg, states) within a country? As an extension of this question, it has been proposed that the quality of the psychosocial environment—characterised by such things as social capital and sense of control over life—is the main explanatory mechanism for such associations.1, 6, 9 Although there is evidence at the individual level that psychosocial factors, like distrust,¹⁰ control,¹¹ and the quality of interpersonal relationships¹² affect health, little is known about whether population level analogues of these psychosocial factors explain health differences between countries. Such psychosocial indicators have been shown as unimportant in understanding between country differences in self-rated health.¹³ The second question is that if an association does exist between income inequality and health at the population level, to what extent is that association the mathematical result of the underlying association between income and health at an individual level.14, 15 Several within USA studies have investigated aspects of this.15, 16 The present analyses investigate the first question.

The theory that income inequality, and its potential effect on aspects of the psychosocial environment, can account for international health differences has become influential for interpreting health inequalities and in a number of countries has been embraced in policy documents focused on strategies to improve population health.³ Interest in the health effects of unequal income distribution was generated by the observation that income inequality was strongly associated with life expectancy among nine Organisation for Economic Cooperation and Development (OECD) nations.⁵ These data from the late 1970s and early 1980s showed that more economically unequal countries like the USA and UK had lower life expectancy than more egalitarian Nordic countries. After publication of this provocative idea, concerns were raised about accuracy of the income data, and contrary findings were published.17, 18, 19, 20, 21 Despite the fact that these studies produced inconsistent findings, the theory that income inequality and its psychosocial effects are critical determinants of population health continues to be generally accepted and widely promoted.22, 23, 24

Important questions remain about the underlying empirical evidence to support claims that countries with more income inequality and poorer psychosocial environment have worse population health. Previous research has been based on small numbers of countries and limited health indicators, such as life expectancy—a synthetic, overall measure of population health which can mask differences in the age and cause of death structure between countries. Across Europe, between country differences in the cause of death structure have been shown to be important in interpreting differences in the extent of within country health inequalities.²⁵

We aimed to assess 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 of the Luxembourg Income Study (LIS). The LIS is widely regarded as the premier study of income distribution in the world.²⁶ We have also examined how aspects of the psychosocial environment such as distrust, belonging to organisations, volunteering (all proposed as measures of social capital,²⁷ and perceived control over one's life circumstances were associated with between-country variations in health. We have also included data on belonging to trade unions and the proportion of women elected to national government, as indicators of class relations within the labour market and broader sociopolitical participation of women.²⁸

Section snippets

Country selection

Wave III (1989–92) of the LIS provides the most recent, complete income inequality data available and includes 23 countries—Taiwan, Czech republic, Hungary, Israel, Poland, Russia, Slovak republic, Australia, Belgium, Canada, Denmark, Finland, France, Germany, Italy, Luxembourg, Netherlands, Norway, Spain, Sweden, Switzerland, UK, and USA. Taiwan was excluded because health data were not available. We first examined income inequality and life expectancy among the remaining 22 countries.

Results

We first examined data on income inequality and life expectancy for 22 countries in the wave III LIS database, As we have argued elsewhere, when data points are few, the selection of countries can be crucial to interpretation of results.³⁴ Thus, we have presented data from all available countries in figure 1, which shows that income inequality was strongly and negatively associated with life expectancy (p=0·0001). However, this association was largely induced by the data point for Russia, where

Discussion

There are inherent limitations in interpreting associations based on sixteen, or fewer observations. To illustrate this point, in figure 2A we have selected the nine countries that were used in the 1992⁵ study which reported a correlation of r=0·86 between more equal income distribution and life expectancy from data for the late 1970s and early 1980s. When we used these same nine countries but analysed data for 1989–92, higher income inequality was associated with lower life expectancy, albeit

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ArticlesIncome inequality, the psychosocial environment, and health: comparisons of wealthy nations

Summary

Background

Methods

Findings

Interpretation

Introduction

Section snippets

Country selection

Results

Discussion

Unhealthy societies: the afflictions of inequality

Income inequality and mortality: why are they related? Income inequality goes hand in hand with underinvestment in human resources

BMJ

Income inequality and mortality: importance to health of individual income, psychosocial environment, or material conditions

BMJ

Income inequality and health: what does the literature tell us?

Anmt Rev Public Health

Income distribution and life expectancy

BMJ

International comparators and poverty and health in Europe

BMJ

Inequality in income and mortality in the United States: analysis of mortality and potential pathways

BMJ

Income distribution and mortality: cross-sectional ecological study of the Robin Hood index in the United States

BMJ

Social capital, income inequality, and mortality

Am J Public Health

Hostility and increased risk of mortality and acute myocardial infarction: the mediating role of behavioural risk factors

Am J Epidenriol