Aged Garlic Extract Supplementation Reduces Blood Pressure Clinical Trial Shows


  • Garlic (Allium sativum)
  • Blood Pressure
  • Hypertension
Date: 02-15-2013 HC# 011351-466

Re:  Clinical Trial Shows Aged Garlic Extract Supplementation Reduces Blood Pressure 

Ried K, Frank OR, Stocks NP. Aged garlic extract reduces blood pressure in hypertensives: a dose-response trial. Eur J Clin Nutr. January 2013;67(1):64-70. 

Standard treatment with antihypertensive (high blood pressure) medication is not effective in all people. Studies show that aged garlic (Allium sativum) supplements can lower blood pressure. [Note: Garlic powder, garlic oil, raw garlic, and cooked garlic are not the preparation of choice for blood pressure treatment.] Aged garlic extract contains S-allyl cysteine, which is the putative active and stable component used for standardization. The purpose of this randomized, double-blind, placebo-controlled study was to evaluate the effect and tolerability of several doses of aged garlic extract as an adjunct treatment to patients with uncontrolled hypertension. 

Patients (n = 84; mean age: 70 years) with uncontrolled hypertension (systolic blood pressure [SBP] ≥ 135 mmHg in the past 6 months) from 2 general practices in Adelaide, South Australia participated in this study conducted from August 2011 to March 2012. Included patients were taking prescription antihypertensive medication for ≥ 2 months and their general practitioners were not planning to change the medication plan during the trial. Excluded patients had an unstable or serious illness or were taking garlic supplements. Patients received 1, 2, or 4 capsules/day of Kyolic® High Potency Everyday Formula 112 (Wakunaga/Wagner; Sydney, Australia), containing either 240, 480, or 960 mg of aged garlic extract and 0.6, 1.2, or 2.4 mg S-allyl cysteine, respectively, or placebo for 12 weeks. Sachets with a drop of liquid Kyolic were added to the placebo containers with the intention of blinding the garlic odor. Patients were instructed to take their usual prescription medication. The primary outcome measures were SBP and diastolic blood pressure (DBP) at 4, 8, and 12 weeks compared with baseline. 

The baseline characteristics were similar between groups. Patients took an average of 2 different types of antihypertensive medications. At 12 weeks, the 2-capsule group had a significant reduction in SBP compared with placebo (P = 0.03). There was no change in DBP. The authors conducted an additional analysis which excluded 6 patients from the data set. These patients had blood pressure medication changes or poor compliance. In the additional analysis, the 2-capsule group had a significant reduction in SBP compared with placebo at both 8 and 12 weeks (P < 0.01). There was no significant improvement in the 1-capsule or 4-capsule group compared with placebo at any time point in either analysis. Across all groups, blood pressure changed from -40 to +5 mmHg. SBP did not change by > 5 mmHg in one-third of the participants. This finding was not associated with gender, age, body mass index, smoking status, or the number of blood pressure medications. One-third of the patients correctly guessed their treatment allocation. Participants in the garlic groups reported minor complaints in the first week of the trial, including constipation, bloating, flatulence, reflux, garlic taste, and difficulty swallowing the capsules (23%). A larger number of participants reported adverse side effects in the 4-capsule garlic group compared with the other garlic groups, but the difference was not statistically significant. 

The authors conclude that this aged garlic extract was superior to placebo in lowering SBP in patients with uncontrolled hypertension. The 2-capsule dose was effective and well tolerated. The authors think that the effect was clinically significant because the 10% improvement in SBP is known to be associated with a decreased risk in cardiovascular disease. The authors state that the study was not powered to detect a difference in DBP because the patients were selected based on their SBP. It is currently thought that DBP is an important predictor of cardiovascular disease and may be a more important determinant than SBP. The authors should re-examine the 2-capsule dose in a sample powered to detect differences in SBP to determine whether aged garlic has an effect on DBP. 

—Heather S. Oliff, PhD
first appeared