Fasting Blood Glucose Predicts Incidence of Hypertension Independent of HbA1c Levels and Insulin Resistance in Middle-Aged Japanese: The Saku Study

BACKGROUND Relationships between blood glucose (BG) levels and insulin action, and incidence of hypertension have not been well known epidemiologically. This study aimed to investigate the association between indices of diabetes and the incidence of hypertension and compare the predictive powers of these indices in middle-aged Japanese. METHODS This 5-year cohort study included 2,210 Japanese aged 30-64 years without hypertension. Hazard ratios of high fasting blood glucose (FBG) levels, high post-loaded BG levels, high glycated hemoglobin (HbA1c) levels, insulin resistance (defined by homeostasis model assessment of insulin resistance [HOMA-IR]) and impaired insulin secretion at baseline for the incidence of hypertension were estimated using multivariable-adjusted Cox proportional hazard models. Hypertension was defined as blood pressure >= 140/90 mm Hg or receiving antihypertensive treatment. RESULTS During the follow-up, 456 participants developed hypertension. After adjustment for HbA1c and HOMA-IR, FBG was independently and significantly associated with hypertension. The hazard ratio of participants with FBG >= 7.0 mmol/l was 1.79 compared with those with FBG < 5.6 mmol/l. Even among those with HbA1c < 6.5%, HOMA-IR < 2.5, body mass index < 25 kg/m(2), age < 55 years old, blood pressure < 130/80 mm Hg or non- and moderate drinking, the results were similar. High 120-minute BG level and impaired insulin secretion did not increase the risk for hypertension. CONCLUSIONS FBG was a predictable index for future incidence of hypertension in middle-aged Japanese men and women. This is the first study comparing predictive powers of indices of diabetes for the incidence of hypertension.