Relative deprivation in income and mortality by leading causes among older Japanese men and women: AGES cohort study

BACKGROUND: Relative deprivation of income is hypothesised to generate frustration and stress through upward social comparison with one's peers. If psychosocial stress is the mechanism, relative deprivation should be more strongly associated with specific health outcomes, such as cardiovascular disease (compared with other health outcomes, eg, non-tobacco-related cancer). METHODS: We evaluated the association between relative income deprivation and mortality by leading causes, using a cohort of 21 031 community-dwelling adults aged 65 years or older. A baseline mail-in survey was conducted in 2003. Information on cause-specific mortality was obtained from death certificates. Our relative deprivation measure was the Yitzhaki Index, derived from the aggregate income shortfall for each person, relative to individuals with higher incomes in that person's reference group. Reference groups were defined according to gender, age group and same municipality of residence. RESULTS: We identified 1682 deaths during the 4.5 years of follow-up. A Cox regression demonstrated that, after controlling for demographic, health and socioeconomic factors including income, the HR for death from cardiovascular diseases per SD increase in relative deprivation was 1.50 (95% CI 1.09 to 2.08) in men, whereas HRs for mortality by cancer and other diseases were close to the null value. Additional adjustment for depressive symptoms and health behaviours (eg, smoking and preventive care utilisation) attenuated the excess risks for mortality from cardiovascular disease by 9%. Relative deprivation was not associated with mortality for women. CONCLUSIONS: The results partially support our hypothesised mechanism: relative deprivation increases health risks via psychosocial stress among men.