Educational level as a predictor of the incidences of non-communicable diseases among middle-aged Japanese: a hazards-model analysis

BACKGROUND: It is well known that there are educational inequalities in incidences of non-communicable diseases (NCDs). Unlike most preceding studies, this study examined this issue using a hazards model analysis, with specific reference to the potential mediating effects of socioeconomic status (SES), other than educational level, and health behaviour as well as gender differences. METHODS: Data were obtained from a 12-wave longitudinal nationwide survey conducted from 2005 to 2016 with middle-aged individuals in Japan. Participants included 31,210 individuals (15,127 men and 16,083 women) who were aged 50–59 years at wave 1. Incidences of six NCDs (diabetes, heart disease, stroke, hypertension, hyperlipidaemia, and cancer), initially diagnosed between waves 2 and 12, were considered. Cox proportional hazards models were estimated to examine their associations with educational level, adjusted for baseline SES and health behaviour. Educational inequalities were measured by the relative indices of inequality (RII). RESULTS: Lower educational level was associated with higher incidences of diabetes and stroke among both men and women, and with hypertension only among women. After controlling for baseline SES, health behaviour, and regional areas, the RII ranged from 1.37 (95% confidence interval [CI]: 1.02–1.85) for stroke among men to 2.65 (95% CI, 2.09–3.36) for diabetes among women. Small to moderate parts (0.0–32.7%) of the RII were explained by baseline SES and health behaviour. A negative association with education was observed for diabetes and hypertension among women. CONCLUSIONS: Results underscored the importance of educational level as a predictor of the incidences of selected NCDs, especially among women, with limited mediating effects of other SES and health behaviour.