Objectives The quantitative associations between prehypertension or its separate blood pressure (BP) ranges and the risk of main cardiovascular outcomes, including stroke, coronary heart disease (CHD), myocardial infarction (MI) and total cardiovascular disease (CVD) events, as well as diabetes, have not been reliably documented. We aim to qualitatively and quantitatively assess these relationships through a systematic review and meta-analysis of prospective cohort studies.
Methods We performed a comprehensive search of PubMed (1966-June 2012) and the Cochrane Library (1988-June 2012) without language restrictions. This was supplemented by review of reference lists of original and relevant reviews. Prospective studies were included if they reported multivariate-adjusted risk ratios (RRs) and corresponding 95% confidence intervals (CIs) of desirable outcomes (i.e. fatal or non-fatal incident stroke, CHD, MI, total CVD events and diabetes) with respect to prehypertension or its separate BP ranges (low range: 120-129/80-84 mmHg; high range: 130–139/85–89 mmHg) at baseline. After the related data were extracted by two investigators independently, pooled RRs were estimated using a random-effects model or a fixed-effects model. Publication bias was evaluated, and sensitivity and subgroup analyses were performed.
Results Thirty-two articles met our inclusion criteria, with 1,010,858 participants. Both low- and high-range prehypertension were associated with a greater risk of developing or dying of total CVD (low-range: RR: 1.24; 95% CI: 1.10 to 1.39; high range: RR: 1.56; 95% CI: 1.36 to 1.78). Low-range prehypertension was associated with a greater risk of stroke (RR: 1.35; 95% CI: 1.10 to 1.66, P = 0.004), and high-range prehypertensinon was related to a much higher risk (RR: 1.95; 95% CI: 1.69 to 2.24, P < 0.001). Both two ranges in prehypertension increased the risk of MI (low range: RR: 1.43; 95% CI: 1.10 to 1.86; high range: RR: 1.99; 95% CI: 1.59 to 2.50). The whole range prehypertension had a 1.44-, 1.73-, 1.34- and 1.79-fold risk of total CVD, stroke, CHD and MI, respectively. Prehypertennsion was not significantly associated with incident diabetes (RR: 1.25; 95% CI: 0.99 to 1.57). There was no evidence of publication bias. The effects of prehypertension on CVD outcomes differed by many factors, such as gender, age group and study quality.
Conclusions Prehypertensive patients have a greater risk of incident stroke, MI and total CVD events, even within the lower range. More attention needs to be paid to this high risk population. Trials investigating the effects of BP reduction on CVD outcomes among prehypertensive patients are expected.