Individual income, income distribution, and self rated health in Japan: cross sectional analysis of nationally representative sample

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Abstract
Objective: To assess the effects on self rated health of individual income and income distribution in Japan. Design: Cross sectional analysis. Data collected on household income, self rated health, and other sociodemographic characteristics at the individual level from comprehensive survey of the living conditions of people on health and welfare in a nationally representative sample from each prefecture. Setting: Prefectures in Japan. Participants: 80 899 people aged >15 years with full records in survey. Main outcome measures: Dichotomous variable for self rated health of each respondent (0 if excellent, very good or good; 1 if fair or poor). Results: Inequality in income at the prefecture level measured by the Gini coefficient was comparable with that in other industrialised countries. Unadjusted odds ratios show a 14% increased risk (odds ratio 1.14, 95% confidence interval 1.02 to 1.27) in reporting poor or fair health for individuals living in prefectures with higher inequality in income. After adjustment, individual income was more strongly associated with self rated health than income inequality. Additional inclusion of regional effects showed that median income at the prefecture level was inversely related to self rated health. Conclusions: Individual income, probably relative to the median prefecture income, has a stronger association with self rated health than income inequality at the prefecture level. What is already known on this topic Contrary to the common perception of an egalitarian society, income inequality in Japan has increased rapidly since the late 1980s, though life expectancy continues to increase Individual level studies, exclusively carried out in the United States to assess the independent effects of income inequality on health, have had mixed results What this study adds Individual income levels, probably relative to regional median income, may have more influence on an individual's perceived health than regional income inequality in Japan