Descriptive Epidemiology of Diabetes Prevalence and HbA1c Distributions Based on a Self-Reported Questionnaire and a Health Checkup in the JPHC Diabetes Study

BACKGROUND The present study examined the prevalence of diabetes in Japan during the late 1990s and early 2000s using the Japan Public Health Center-based Prospective Diabetes cohort. We also investigated the distributions of HbA1c values in noncompliant diabetic participants in the cohort. METHODS A total of 28 183 registered inhabitants aged 46-75 years from 10 public health center areas were included in the initial survey. The 5-year follow-up survey included 20 129 participants. The prevalence of diabetes was estimated using both a self-reported questionnaire and laboratory measurements. Among the participants who reported the presence of diabetes on the questionnaire (self-reported diabetes), the distributions of HbA1c values were described according to their treatment status. RESULTS The age-standardized prevalence of diabetes in 55- to 74-year-old adults was 8.2% at the initial survey and 10.6% at the 5-year follow-up. At the initial survey, among participants with self-reported diabetes, the mean HbA1c values in the participants who had never and who had previously received diabetes treatment were 7.01% (standard deviation [SD] 1.56%) and 6.56% (SD 1.46%), respectively. Approximately 15% of the participants who had self-reported diabetes but had never received diabetes treatment had an HbA1c ≥ 8.4%. CONCLUSIONS The prevalence of diabetes increased in the JPHC cohort between the late 1990s and early 2000s. A certain proportion of participants who were aware of their diabetes but were not currently receiving treatment had poor diabetic control. Efforts to promote continuous medical attendance for diabetes care may be necessary.