Benefits
Blood pressure in placebo-controlled trials
In a 12-week trial of 88 adults with uncontrolled high blood pressure, most on medication, 1.2 g a day lowered systolic pressure 5.0 mmHg more than placebo; diastolic did not differ. In a dose-response trial, only the 480 mg dose beat placebo, by 11.8 mmHg systolic. Pooled across 19 aged garlic trials, systolic fell 2.49 mmHg and diastolic did not change. The maker funded the larger trial.
Cholesterol and LDL in placebo-controlled trials
Results differ by trial. In a six-month government-funded trial of 192 adults with raised LDL, aged garlic extract at about one clove's equivalent did not lower LDL compared with placebo. Pooled across aged garlic trials, LDL fell about 4.4 mg/dL while the total cholesterol change fell short of statistical significance. A six-week trial in 51 adults with obesity reported lower LDL than placebo.
Coronary artery calcium and plaque on heart scans
In two one-year trials at 2.4 g a day, one found less growth in one of four coronary plaque measures and the other found people more likely than on placebo to fall in the slower calcium-progression half. A third trial used a capsule that also held B vitamins and L-arginine, so its result cannot be credited to garlic alone. The maker supported both garlic-only trials, and none of the three counted heart attacks or strokes.
Immune cell activity in placebo-controlled trials
In a 90-day trial of 120 healthy adults taking 2.56 g a day, colds and flu were not less frequent than on placebo; among illnesses that did occur, the garlic group logged 21% fewer symptoms and 58% fewer missed work or school days. Two immune cell types grew better in lab tests. A six-week trial in 51 adults with obesity found more gamma-delta T cells but no change in NK cells. Limited evidence from two small maker-backed trials.
Gum health measures in a placebo-controlled trial
In a four-month examiner-blind trial, 151 adults took aged garlic extract or placebo, and 134 finished. Gum inflammation and gum bleeding index scores fell more with the extract than with placebo. The abstract does not give the daily dose, and the authors state they have no financial interest in the product or in the company that sponsored the study, which the abstract does not name.
Mechanism of action
S-allylcysteine and the aging process
A review by a Wakunaga scientist explains that the odorous allicin-type compounds of crushed garlic break down during processing, and that long-term extraction forms S-allylcysteine, S-allylmercaptocysteine, saponins and other compounds. Aged extracts are standardized to S-allylcysteine; the trial capsules listed 0.6 to 2.4 mg per daily dose.
Platelet aggregation and adhesion
In a randomized double-blind dose-finding study in 34 healthy adults taking 2.4 to 7.2 g a day, aged garlic extract moderately raised the thresholds for platelet aggregation triggered by epinephrine and collagen and reduced platelet adhesion to fibrinogen at every dose. These are laboratory measures of platelet function, not bleeding events.
Inflammatory markers
In a six-week trial in adults with obesity, blood IL-6 and TNF-alpha were lower on aged garlic extract than on placebo, and a one-year heart scan trial found more people in the lowest IL-6 group with the extract. These are blood markers, not measures of how people felt.
Clinical trials
Double-blind randomized placebo-controlled trial of Kyolic aged garlic extract at one, two or four capsules a day (240, 480 or 960 mg, providing 0.6, 1.2 or 2.4 mg S-allylcysteine) added to existing blood pressure medication in general practice patients with uncontrolled systolic hypertension. Supported by a hospital research grant; capsules were provided by the Australian distributor Vitaco Health, which the paper says was not involved in the study. (Ried et al. 2013, Eur J Clin Nutr)
79 general practice patients with uncontrolled systolic hypertension, most already taking blood pressure medication. 12 weeks.
Systolic blood pressure fell 11.8 mmHg more than placebo in the two-capsule (480 mg) group. The four-capsule group showed a 7.4 mmHg fall at 8 weeks that did not reach significance (P=0.07), and the one-capsule group and diastolic pressure did not differ from placebo.
Placebo-controlled double-blind randomized trial, 2005 to 2007, of one daily capsule combining aged garlic extract 250 mg with vitamin B12 100 mcg, folic acid 300 mcg, vitamin B6 12.5 mg and L-arginine 100 mg, so the result cannot be credited to aged garlic extract alone. Outcomes were coronary artery calcium progression on CT, a vascular reactivity index, lipids and oxidation markers. Total cholesterol, LDL and homocysteine fell relative to placebo, while HDL, oxidized phospholipids on apoB and Lp(a) rose. Funding is not stated in the abstract. (Budoff et al. 2009, Prev Med)
65 intermediate-risk adults, mean age 60, 79% men. One year.
Calcium score progression was lower and a temperature-rebound reactivity index higher than with placebo after adjustment for risk factors (P<0.05); blood marker results are in the study details. No clinical events were counted.
Double-blind randomized placebo-controlled trial of Kyolic aged garlic extract, 1.2 g/day providing 1.2 mg S-allylcysteine, for 12 weeks; 72% of participants were on blood pressure medication and 25% on blood-thinning medication. Supported by a grant from Wakunaga of America, which makes the extract, supplied the capsules and funded tests and research assistance; the paper states the company had no role in design, analysis or writing. (Ried et al. 2016, Integr Blood Press Control)
88 general practice patients and community members with uncontrolled hypertension. 12 weeks.
Mean systolic blood pressure fell 5.0 mmHg more than with placebo (P=0.016); the overall diastolic difference was not significant. A post-hoc responder subgroup showed larger falls, 11.5 mmHg systolic and 6.3 mmHg diastolic, but a subgroup chosen because it responded is not a fair estimate of the average effect. Dropout was 22% on placebo and 9% on garlic. Central pressure, arterial stiffness and cholesterol only trended in garlic's favor.
Prospective randomized double-blind trial of aged garlic extract 2,400 mg/day versus placebo in adults with metabolic syndrome, with cardiac CT angiography at baseline and about a year later. Funded by Wakunaga of America, which makes the extract. ClinicalTrials.gov NCT01534910. (Matsumoto et al. 2016, J Nutr)
55 adults, mean age 59, 71% men; 27 on the extract and 28 on placebo. Scans about 354 days apart.
Low-attenuation plaque, one of four plaque measures, fell 1.5% with aged garlic extract while rising 0.2% on placebo (P=0.0049). The other three measures showed no difference between groups: total plaque volume, non-calcified plaque, and calcified plaque, which changed by 0.2% in both arms. No heart attacks, strokes or deaths were counted, and the authors call for further studies on whether the change matters.
Single-center randomized double-blind placebo-controlled trial of Kyolic aged garlic extract 2,400 mg/day for one year in adults with a Framingham risk score of 10 or more; primary outcome change in coronary artery calcium score, analyzed as the odds of falling in the lower-progression group. Funded by two Swedish foundations and a research grant from Wakunaga of America, which also supplied the capsules; registered retrospectively as NCT03860350. (Wlosinska et al. 2020, BMC Complement Med Ther)
104 adults randomized, 93 analyzed. One year.
People on aged garlic extract were 2.95 times as likely to fall in the slower calcium-progression group (95% CI 1.05 to 8.27). Systolic blood pressure fell from 148 to 140 mmHg within the garlic group and did not change on placebo; the lipid profile and CRP did not differ between groups. The garlic group started with higher calcium scores.
Parallel four-arm randomized trial of raw garlic, a powdered garlic supplement, an aged garlic extract supplement or placebo, each at about one 4 g clove equivalent, 6 days a week for 6 months, in adults with LDL cholesterol of 130 to 190 mg/dL; primary outcome LDL cholesterol; funded by the US National Institutes of Health. (Gardner et al. 2007, Arch Intern Med)
192 adults; 87% to 90% retention in all four arms.
None of the three garlic forms changed the primary outcome compared with placebo. Six-month mean changes were +0.4 mg/dL with raw garlic, +3.2 with the powder and +0.2 with aged extract, against -3.9 on placebo. No secondary blood fat measure differed between groups either.
Randomized, double-blind, placebo-controlled trial of encapsulated aged garlic extract 2.56 g/day versus placebo over 90 days of the cold and flu season; the primary aim was immune cell proliferation, and illness incidence was a secondary outcome. Registered as NCT01390116, which lists Wakunaga Pharmaceutical, the extract's maker, as an industry collaborator. (Nantz et al. 2012, Clin Nutr)
120 healthy adults, 60 per group; cell measurements in a 56-person subset.
The number of colds and flu episodes did not differ significantly from placebo. Among the illnesses that did occur, the garlic group logged 21% fewer symptoms, 61% fewer days functioning sub-optimally and 58% fewer missed work or school days. Gamma-delta T cell and NK cell proliferation were greater than placebo at 45 days. Cells proliferating in a laboratory assay are not the same as getting sick less often.
Parallel double-blind placebo-controlled randomized trial of aged garlic extract 3.6 g/day, taken in divided doses with food for 6 weeks; registered as NCT01959646 with the University of Florida as sponsor. The publisher's funding record lists Wakunaga of America, which makes the extract, as funder. The extract group also had lower LDL than placebo (P=0.05), while total and non-HDL cholesterol did not differ. (Xu et al. 2018, Clin Nutr ESPEN)
51 healthy adults with obesity, mean age 46, mean BMI 36.
Serum IL-6 and TNF-alpha were lower than on placebo at the end of the study. The garlic group had a higher proportion of gamma-delta T cells and a lower proportion of NKT cells, with no difference in the percentage of NK cells.
Randomized, examiner-blind, two-group parallel trial of aged garlic extract versus placebo for four months, with three calibrated examiners; the daily dose is not given in the abstract. The authors state they have no financial interest in the product or in the company sponsoring the study, which is not named in the abstract. (Zini et al. 2018, J Clin Dent)
151 adults, average age 33, 50% men; 134 completed.
Modified Gingival Index and Gingival Bleeding Index scores fell more with aged garlic extract than with placebo (P<0.001).