Objectives: The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC7) defined blood pressure (BP) levels of 120-139/80-89 mmHg as prehypertension. The objective of the present analysis was to examine the impact of prehypertension and its population-attributable fraction for development of cardiovascular events in a general Japanese population. Methods: Two thousand, six hundred and thirty-four residents of the town of Hisayama aged at least 40 years without cardiovascular disease were followed up for 19 years. BP categories were defined using JNC7, and prehypertension was divided into the lower (120-129/80-84 mmHg) and higher ranges (130-139/85-89 mmHg). During the follow-up period, 449 participants developed cardiovascular disease (305 strokes and 187 coronary heart diseases). Results: The frequencies of normal BP, prehypertension, and stages 1 and 2 hypertension were 24.9, 37.7, 23.8, and 13.6%, respectively. The age and sex-adjusted incidence of cardiovascular disease rose progressively with elevation of BP levels (P < 0.001 for trend). The risks of cardiovascular disease in lower and higher ranges of prehypertension were 58% [95% confidence interval (CI) 11-126%] and 70% (95% CI 18-144%) higher than normal BP even after controlling for other cardiovascular risk factors. The population-attributable fraction of prehypertension was 13.2%, which was similar to those of stages 1 and 2 hypertension. Conclusions: The risks of cardiovascular disease increased significantly from the lower range of prehypertension in a general Japanese population. Approximately one-third of excess cardiovascular events attributable to elevated BP levels were estimated to occur among individuals with prehypertension.
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