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A Randomized Clinical Trial

Christopher D. Gardner, PhD; Larry D. Lawson, PhD; Eric Block, PhD; Lorraine M. Chatterjee, MS; Alexandre Kiazand, MD; Raymond R. Balise, PhD; Helena C. Kraemer, PhD

Arch Intern Med. 2007;167(4):346-353.

Background  Garlic is widely promoted as a cholesterol-lowering agent, but efficacy studies have produced conflicting results. Garlic supplements differ in bioavailability of key phytochemicals. We evaluated the effect of raw garlic and 2 commonly used garlic supplements on cholesterol concentrations in adults with moderate hypercholesterolemia.

Methods  In this parallel-design trial, 192 adults with low-density lipoprotein cholesterol (LDL-C) concentrations of 130 to 190 mg/dL (3.36-4.91 mmol/L) were randomly assigned to 1 of the following 4 treatment arms: raw garlic, powdered garlic supplement, aged garlic extract supplement, or placebo. Garlic product doses equivalent to an average-sized garlic clove were consumed 6 d/wk for 6 months. The primary study outcome was LDL-C concentration. Fasting plasma lipid concentrations were assessed monthly. Extensive chemical characterization of study materials was conducted throughout the trial.

Results  Retention was 87% to 90% in all 4 treatment arms, and chemical stability of study materials was high throughout the trial. There were no statistically significant effects of the 3 forms of garlic on LDL-C concentrations. The 6-month mean (SD) changes in LDL-C concentrations were +0.4 (19.3) mg/dL (+0.01 [0.50] mmol/L), +3.2 (17.2) mg/dL (+0.08 [0.44] mmol/L), +0.2 (17.8) mg/dL (+0.005 [0.46] mmol/L), and –3.9 (16.5) mg/dL (–0.10 [0.43] mmol/L) for raw garlic, powdered supplement, aged extract supplement, and placebo, respectively. There were no statistically significant effects on high-density lipoprotein cholesterol, triglyceride levels, or total cholesterol–high-density lipoprotein cholesterol ratio.

Conclusions  None of the forms of garlic used in this study, including raw garlic, when given at an approximate dose of a 4-g clove per day, 6 d/wk for 6 months, had statistically or clinically significant effects on LDL-C or other plasma lipid concentrations in adults with moderate hypercholesterolemia.

Clinical Trial Registry  http://clinicaltrials.gov Identifier: NCT00056511

Author Affiliations: Stanford Prevention Research Center and Department of Medicine, Stanford University Medical School, Stanford, Calif (Drs Gardner, Kiazand, Balise, and Kraemer and Ms Chatterjee); Plant Bioactives Research Institute, Orem, Utah (Dr Lawson); and Department of Chemistry, University at Albany, State University of New York (Dr Block).

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