Prevalence of type 2 diabetes by age, sex and geographical area among two million public assistance recipients in Japan: a cross-sectional study using a nationally representative claims database

Background Recognising the importance of the social determinants of health, the Japanese government introduced a health management support programme targeted at type 2 diabetes (T2D) for public assistance recipients (PAR) in 2018. However, evidence of the T2D prevalence among PAR is lacking. We aimed to estimate T2D prevalence by age and sex among PAR, compared with the prevalence among health insurance enrollees (HIE). Additionally, regional differences in T2D prevalence among PAR were examined. Methods This was a cross-sectional study using 1-month health insurance claims of both PAR and HIE. The Fact-finding Survey data on Medical Assistance and the National Database of Health Insurance Claims data were used. T2D prevalence among PAR and HIE were assessed by age and sex, respectively. Moreover, to examine regional differences in T2D prevalence of inpatients and outpatients among PAR, T2D crude prevalence and age-standardised prevalence were calculated by prefecture. Multilevel logistic regression analysis was also conducted at the city level. Results T2D crude prevalence was 7.7% in PAR (inpatients and outpatients). Among outpatients, the prevalence was 7.5% in PAR and 4.1% in HIE, respectively. The mean crude prevalence and age-standardised prevalence of T2D (inpatients and outpatients) among 47 prefectures were 7.8% and 3.9%, respectively. In the city-level analysis, the OR for the prevalence of T2D by region ranged from 0.31 to 1.51. Conclusion The prevalence of T2D among PAR was higher than HIE and there were regional differences in the prevalence of PAR. Measures to prevent the progression of diabetes among PAR by region are needed.