To explore potential causes of heterogeneity, we stratified all clinical trials according to age, BMI, study design, randomization, treatment duration, dosage of phenols in grape seed extract, and baseline status of study subjects, respectively (Table (Table2). Of 16 clinical trials, 4 were conducted in patients with pre- and stage 1 hypertension, 4 in healthy subjects, 3 in patients with metabolic syndrome, 2 in hypertensive patients, 2 in women with at least 1 menopausal symptom, and 1 in patients with above-average vascular risk (Supplementary Table S1). Seven trials had grape seed extract treatment 0.05).
Twelve trials were double-blinded and 4 trials were single-blinded. The dosages of grape seed extract agents taken ranged from 100 to 2000 mg/d. Of 16 clinical trials, 12 followed a parallel design and 5 followed a cross-over design. The baseline characteristics of 16 clinical trials are presented in Table Table1 1 and Supplementary Table S1. To help clarify this issue and explore the potential causes of heterogeneity, we systematically evaluated the impact of grape seed extract treatment on blood pressure changes in a meta-analysis of available randomized controlled trials according to the principles stipulated in the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) statement (see the PRISMA checklist).
Many times the conflicting results may arise from differences in sampling strategy, lifestyle modality, dosage of agents, and treatment duration. Several clinical trials have reported a beneficial impact of grape seed extract on blood pressure, while others have not. Today grape seed extract is commercially available on the market, and it is generally well tolerated when taken by mouth. This property is mainly determined by polyphenols, especially proanthocyanidins, contained in grape seed extract, which can well interpret the French paradox that refers to the low rate of coronary heart disease mortality in France people despite the diets being rich in saturated fat. Overwhelming evidence from in vitro experiments suggests that grape seed extract has an antioxidant property that can protect cells from ROS-mediated DNA damage. Agents that can suppress oxidative stress therefore represent an effective therapeutic option for the management and treatment of hypertension. Oxidative stress is defined as an excessive production of reactive oxygen species (ROS) that cannot be quenched by antioxidants. It is widely recognized that oxidative stress is implicated in the pathogenesis of hypertension.
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