Reviewed: Ried K, Frank OR, Stocks NP. Aged garlic extract lowers blood pressure in patients with treated but uncontrolled hypertension: a randomized controlled trial. Maturitas. 2010 Oct;67(2):144-150.

Garlic (Allium sativum, Alliaceae) supplements have been associated with a clinically significant blood pressure-lowering effect in patients with untreated hypertension (systolic blood pressure [SBP] ≥ 140 mm Hg or diastolic blood pressure [DBP] ≥ 90 mm Hg) similar to that achieved by first-line treatment with antihypertensive medication according to 2 systematic reviews and meta-analyses of randomized controlled clinical trials (RCTs) published in 2008.^1,2 A 2009 systematic review questioned the methodological quality of some of these RCTs.³

The antihypertensive properties of garlic have been linked to stimulation of intracellular nitric oxide (NO) and hydrogen sulfide (H2S) production, as well as blockage of angiotensin II production, which promotes vasodilation and reduction in BP.

This double-blind, parallel, randomized, placebo-controlled clinical trial was conducted in Adelaide, South Australia, between March and September 2009 to investigate the effect, tolerability, and acceptability of Aged Garlic Extract^TM (AGE) as an adjunct treatment to existing antihypertensive medication in patients with treated, uncontrolled hypertension. Fifty adult patients (mean age ± standard deviation [SD]: 66 ± 9 years) treated with conventional antihypertensive medications were randomly allocated to the treatment or placebo group for 12 weeks. Patients in the treatment group were assigned 4 capsules daily of Kyolic® AGE (Garlic High Potency Everyday Formula112, Wakunaga/Wagner^®; Vitaco Health [NZ] Ltd; Auckland, New Zealand) containing 960 mg of AGE, equivalent to 2.4 mg SAC. Placebo capsules were matched to the active capsules in number, size, color, and odor. Comparison of baseline characteristics revealed no significant difference between placebo and treatment groups in most parameters and borderline significance in the mean number of BP medication classes prescribed.

Primary outcome measures were SBP and DBP at 4, 8, and 12 weeks compared with baseline. Tolerability of the trial medication was monitored by questionnaire at the 4 weekly appointments, while acceptability and willingness to continue the treatment long term were explored by an exit questionnaire using 5-point Likert-scales and open-ended questions. Statistical significance was set at P < 0.05. Differences between groups at baseline in continuous variables were assessed by Student’s t-test, while categorical variables were assessed by chi-square test, and absolute CVD (cardiovascular disease) risk by Fisher’s Exact test.

A significant treatment effect over 12 weeks was apparent between garlic and control groups in patients with uncontrolled hypertension at baseline (mean difference in SBP ± SD: −10.2 ± 4.3; P = 0.0361), while no significant differences were found in the subgroup of patients with controlled hypertension. Tolerability of trial capsules was generally high, with 24% of the garlic group reporting minor adverse effects including belching, reflux, and taste sensations (P = 0.25). Most of the participants found the treatment easy (93%) and acceptable (92%). Ninety-two percent (92%) of participants in the garlic group were willing to continue taking garlic supplements compared to two-thirds (66%) in the control group.

The authors conclude that AGE’s effectiveness in lowering SBP in patients with uncontrolled, treated hypertension is significantly superior to placebo and similar to common antihypertensive medication. Further research is needed to determine the effectiveness of lower dosages of AGE that would have the benefit of improved tolerability and blinding, as well as reduced costs of treatment. Future larger trials are needed to investigate dose-response relationships and to examine the effect of AGE in association with different conventional BP medication classes.

—Silvia Giovanelli Ris

References

1. Reinhart KM, Coleman CI, Teevan C, Vachhani P, White CM. Effects of garlic on blood pressure in patients with and without systolic hypertension: a meta-analysis. Ann Pharmacother. 2008;42(12):1766-1771.
2. Ried K, Frank OR, Stocks NP, Fakler P, Sullivan T. Effect of garlic on blood pressure: a systematic review and meta-analysis. BMC Cardiovasc Disord. 2008;8:13.
3. Simons S, Wollersheim H, Thien T. “A systematic review on the influence of trial quality on the effect of garlic on blood pressure.” Neth J Med. 2009 Jun;67(6):212-9.