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| Date: 05-13-2016 | HC# 111513-544 |
Li S-H, Zhao P, Tian H-B, Chen L-H, Cui L-Q. Effect of grape polyphenols on blood pressure: a meta-analysis of randomized controlled trials. PLoS One. 2015;10(9): e0137665. doi: 10.1371/journal.pone.0137665.
High blood pressure is a major risk factor for cardiovascular disease. Although studies suggest grape polyphenols may improve hypertension, it is not clear how effective these compounds are in humans. The aim of this meta-analysis was to assess the effect of grape (Vitis vinifera, Vitaceae) fruit polyphenols on blood pressure.
The meta-analysis was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A search for relevant articles containing the words "grape or polyphenol" paired with "blood pressure or hypertension" was conducted in PubMed (from 1950 to March 2015), EMBASE (from 1966 to March 2015), and the Cochrane Library. The selection criteria included the following: the article was published in English; the study was a randomized and controlled trial (RCT) in humans; the subjects were exposed to the intervention for at least two weeks; means of systolic blood pressure (SBP) and diastolic blood pressure (DBP) at the beginning and end of the intervention or the differences between these time periods were reported; and the dose of grape polyphenols was provided. The primary outcome was the overall change in SBP and DBP. Subgroup analyses to identify heterogeneity in the treatment effects were conducted and publication bias was evaluated.
The search identified ten RCTs which met the criteria and were included in the meta-analysis. Eight of the included trials had a double-blind design; one was single blind; and one was not blinded. Cumulatively, 561 subjects were included, with 291 in the grape polyphenol groups and 270 in the control groups. The sample size ranged from nine to 70. Five of the studies included healthy adults, whereas the other five studies included patients with hypertension (n=1), high vascular risk (n=1), metabolic syndrome (n=2), and coronary disease (n=1). The average age of the subjects ranged from 31.4 to 63.7 years old; body mass index varied from 23.2 kg/m2 to 36 kg/m2; the doses of grape polyphenols ranged from 150 mg/d to 1400 mg/d; and the duration of the treatment ranged from two to 16 weeks. Two studies evaluated two doses (low dose and high dose) of grape polyphenols. The different doses were evaluated as independent trials, therefore a total of 12 datasets were analyzed. The quality of the studies ranged from 1 to 4 (0 being the lowest quality and 5 as the highest quality).
Five trials showed a significant reduction in SBP. The meta-analysis of the pooled data indicated that there was a significant reduction in SBP by 1.48 mmHg in the subjects supplemented with grape (P=0.03). No heterogeneity was observed for SBP. Subgroup analyses indicated that SBP was significantly reduced in the group consuming the low dose of grape polyphenols (<733 mg/day) compared to the high dose (P=0.009). SBP was also significantly reduced in patients with metabolic syndrome (n=66) compared to other subgroups (P=0.03).
A total of three trials demonstrated a significant reduction in DBP. However, the meta-analysis indicated that there was no significant change in DBP, and there was no heterogeneity in the treatment effect. Subgroup analyses also indicated no significant differences.
Sensitivity analysis showed the results did not significantly change when the low-quality studies (n=2) were excluded; there was still a significant reduction in SBP (P=0.04) and no significant effect on DBP. No publication bias was found.
The authors conclude that daily supplementation with grape polyphenols can significantly reduce SBP. However, the observed reduction was modest compared to antihypertensive drugs. The following limitations were noted: (1) The sample sizes were relatively small; larger trials are needed to confirm these results. (2) Only one trial included patients with hypertension; additional studies are needed to determine whether the benefits of grape polyphenols may be greater in patients with hypertension. (3) The effects of lifestyle modifications were not evaluated in most of the trials; future studies should control for this variable. (4) Although the subgroup analyses showed that low doses had a greater effect, the doses of the included trials ranged from 150-1400 mg/d; dose-response studies are needed to confirm these findings. (5) While the reduction in SBP was significant, it is not clear whether grape polyphenols also have a beneficial effect on target organs similar to some antihypertensive drugs; the biological actions of grape polyphenols need to be clarified.
—Laura M. Bystrom, PhD
