Effect of garlic (Allium sativum L.) as a functional food, on blood pressure: A meta-analysis of garlic powder, focused on trials for prehypertensive subjects

Purpose: Although numerous systematic reviews or meta-analysis have reported the hypotensive effects of garlic, the application of these results in the area of functional food is limited. This is because the trials used various garlic preparations and patients with differing hypertensive intensities. To validate the use of garlic powder as a blood pressure lowering functional food, we performed the current meta-analysis, focusing on the study of prehypertensive subjects. Methods: Literature search was carried out using various database up to July 2020, including PubMed, Cochrane, ScienceDirect and Korean studies Information Service System, and each study was screened by pre-stated inclusion/exclusion criteria. We identified nine trials that met the eligibility, of which two studies with moderate or high risk of bias were excluded. Results: Meta-analysis of the seven studies revealed that an intake of garlic powder significantly lowered the systolic blood pressure (SBP) and diastolic blood pressure (DBP) by −6.0 mmHg (95% confidence interval [CI], −11.2, −0.8; p = 0.025) and −2.7 mmHg (95% CI, −5.3, −0.1; p = 0.046), respectively. Shapes of the funnel plot for both SBP and DBP seemed symmetrical, and the Egger's regression revealed no publication bias. Moreover, duration of the intervention period was inversely associated with the pooled effects of garlic powder on SBP (p = 0.019) and DBP (p = 0.019), and this result was supported by the subgroup-analysis. The daily dose of garlic powder, baseline value of each biomarker, and subject number, did not moderate the effects on SBP and DBP. Conclusion: Results of the present meta-analysis indicate that garlic powder supplements are superior to placebo for improving the BP in prehypertensive individuals.