High-normal blood pressure and long-term risk of type 2 diabetes: 35-year prospective population based cohort study of men

BACKGROUND: The link between type 2 diabetes and hypertension is well established and the conditions often coexist. High normal blood pressure, defined by WHO-ISH as systolic blood pressure (SBP) 130–139 mm Hg or diastolic blood pressure (DBP) 85–89 mm Hg, has been found to be an independent predictor for type 2 diabetes in studies, although with relatively limited follow-up periods of approximately 10 years. The aim of this study was to investigate whether hypertension, including mildly elevated blood pressure within the normal range, predicted subsequent development of type 2 diabetes in men over an extended follow-up of 35 years. METHODS: Data were derived from the Gothenburg Primary Prevention Study where a random sample of 7 494 men aged 47–55 years underwent a baseline screening investigation in the period 1970–1973. A total of 7 333 men were free from previous history of diabetes at baseline. During a 35-year follow-up diabetes was identified through the Swedish hospital discharge and death registries. The cumulative risk of diabetes adjusted for age and competing risk of death was calculated. Using Cox proportional hazard models we calculated the multiple adjusted hazard ratios (HR) (95% confidence interval (CI)) for diabetes at different blood pressure levels. RESULTS: During a 35-year follow-up, 956 men (13%) were identified with diabetes. The 35-year cumulative risk of diabetes after adjusting for age and competing risk of death in men with SBP levels <130 mm Hg, 130–139 mm Hg, 140–159 mm Hg and ≥160 mm Hg were 19%, 30%, 31% and 49%, respectively. The HR for diabetes adjusted for age, body mass index (BMI), cholesterol, antihypertensive treatment, smoking, physical activity and occupation were 1.43 (95% CI 1.12-1.84), 1.43 (95% CI 1.14-1.79) and 1.95 (95% CI 1.55-2.46) for men with SBP 130–139 mm Hg, 140–159 mm Hg, and ≥ 160 mm Hg, respectively (reference; SBP<130 mm Hg). CONCLUSION: In this population, at mid-life, even high-normal SBP levels were shown to be a significant predictor of type 2 diabetes, independently of BMI and other conventional type 2 diabetes risk factors over an extended follow-up.