Background Japan is considered to be an archetype of social equality, but social and income inequalities expanded recently. Adverse social and economic changes and liberalisation of labour market regulations took place in the 1990s which disturbed the delicate balance between formal and informal policies and resources. Some ecological studies reported the change of health inequality trend around the late 1990s - from narrowing to expanding the gap, but there is no study using data after 2001.
Objective To present the first evidence of health inequality time trends in Japan in individual level data including after 2001; to evaluate the influence of social changes in the 1990s on health inequalities.
Hypothesis Health inequalities have increased since around 2000 as a result of increased income and social inequalities in the 1990s.
Design Pooled data of eight independent national representative surveys (1986–2007)
Setting Japan Participants: Men and women aged 20–59, n=416,115
Outcome Dichotomised self-rated health (SRH) (0=excellent, very good or good, 1=fair or poor)
Methods Age-standardised prevalence of poorer SRH was calculated by direct method; Slope and Relative Index of Inequality ((SII) (RII), respectively) in association with income hierarchy were obtained by generalised linear and logistic regression.
Results Age-standardised prevalence of poorer SRH increased from approximately 8% in the early 1990s to around 12% in 2007 in men and women. SII was 3.5 to 5.2% in the early 1990s in men and women. SII was the smallest in 2001, around 2.5% in both sexes. SII reached 5.8% (CI 3.9 to 7.6) in men and 5.1% (CI 3.3 to 7.0) in women in 2007. There was an evidence of non-linear trend in SII: SII declined from 1986 to 2001, and increased since then (p<0.05). These SII trends remained significant in older working age men and women after adjusting for age and marital status. RII was the smallest in 2001: 1.36 (CI 1.15 to 1.61) in men and 1.32 (CI 1.14 to 1.53), in women. RII trends declined from 1986 to 2001 in both sexes (p<0.05) and increased 33% by 2007 in men (p<0.05). The RII trends attenuated by adjustment for age and marital status, but remained significant in women (p<0.05) and marginally significant in men (p<0.1) in older working age.
Conclusion The changes in prevalence of poorer SRH could correspond with short-term economic cycle. V-shaped trends of SII and RII confirmed the hypothesis. The changes in social arrangements in addition to expanded income inequalities may be responsible in increased health inequalities.
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