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

Standard hypertension treatment with medication that lowers high blood pressure is ineffective in some people. Studies show that aged garlic (Allium sativum, Liliaceae) supplements can lower blood pressure. Aged Garlic Extract™ contains S-allylcysteine, a bioavailable and stable water-soluble organosulfur compound. The purpose of this randomized, double-blind, placebo-controlled study was to evaluate the effect and tolerability of different doses of Aged Garlic Extract as an adjunct treatment for patients with uncontrolled hypertension.

Seventy-nine patients (mean age: 70 years) with uncontrolled hypertension (systolic blood pressure [SBP] ≥ 140 mmHg in the past six months) from two general practices in Adelaide, South Australia, participated in this study conducted from August 2011 to March 2012. Included patients had taken prescription antihypertensive medication for two months or longer, and their general practitioners did not intend to change the medication plan during the trial. Excluded patients had an unstable or serious illness or already were taking garlic supplements. Patients received one, two, or four capsules per day of Kyolic^® High Potency Everyday Formula 112 (Wakunaga/Wagner; Sydney, Australia; Kyolic^® Aged Garlic Extract is produced in Japan by Wakunaga), containing 240, 480, or 960 mg of Aged Garlic Extract (AGE) and 0.6, 1.2, or 2.4 mg Sallylcysteine, respectively, or placebo, for 12 weeks. Sachets with a drop of liquid Kyolic were added to the placebo containers as a method of blinding. Patients were instructed to take their usual prescription medication.

The primary outcome measures were SBP and diastolic blood pressure (DBP) at four, eight, and 12 weeks compared to baseline. The baseline characteristics were similar between groups. Patients took an average of two different types of antihypertensive medications. At 12 weeks, the two-capsule (480 mg) group showed a significant reduction in SBP compared to placebo (P=0.03). There was no change in DBP. The authors conducted an additional analysis that excluded five patients from the data set who had blood pressure medication changes or poor compliance. In this additional analysis, the two-capsule group had a significant reduction in SBP compared to placebo at both eight and 12 weeks (P=0.006). There was no significant improvement in the one-capsule or four-capsule group compared with placebo at any 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 unassociated with sex, age, body mass index, smoking status, or 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 percent). The difference in reported minor adverse side effects between those taking garlic capsules and those taking the placebo was not statistically significant.

The authors concluded that AGE was superior to placebo in lowering SBP in patients with uncontrolled hypertension. The two-capsule dose was effective and well tolerated. The authors wrote that the effect was clinically significant because the 10 percent improvement in SBP is known to be associated with a decreased risk in cardiovascular disease. The authors stated that the study was not powered to detect a difference in DBP because the patients were selected based on their SBP. Currently, it is 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 two-capsule dose in a patient sample powered to determine whether AGE has an effect on DBP.