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Effect of Garlic on Total Serum Cholesterol: A Meta-Analysis

Stephen Warshafsky, MD; Russell S. Kamer, MD; and Steven L. Sivak, MD
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From New York Medical College, Valhalla, New York. Requests for Reprints: Stephen Warshafsky, MD, Section of General Internal Medicine, Department of Medicine, New York Medical College, Valhalla, NY 10595. Acknowledgments: The authors thank Benjamin Littenberg, MD, for critical review of an earlier version of this manuscript and the Internal Medicine residents of Westchester County Medical Center, New York Medical College, for review of studies for the quality score.

Copyright 2004 by the American College of Physicians

Ann Intern Med. 1993;119(7_Part_1):599-605. doi:10.7326/0003-4819-119-7_Part_1-199310010-00009
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Objective: To assess the size and consistency of garlic's effect on total serum cholesterol in persons with cholesterol levels greater than 5.17 mmol/L (200 mg/dL).

Data Sources: Clinical trials were identified by a computerized literature search of MEDLINE and by an assessment of the bibliographies of published studies and reviews.

Study Selection: Trials were selected if they were randomized and placebo-controlled and if at least 75% of their patients had cholesterol levels greater than 5.17 mmol/L (200 mg/dL). Studies were excluded if they did not provide enough data to compute effect size. Five of 28 studies were selected for review.

Data Extraction: Details of study design, patient characteristics, interventions, duration of therapy, and cholesterol measurements were extracted by one author and were verified by another.

Data Synthesis: Study quality was evaluated by multiple reviewers using a closed-ended questionnaire. Patients treated with garlic consistently showed a greater decrease in total cholesterol levels compared with those receiving placebo. Meta-analysis of homogeneous trials estimated a net cholesterol decrease attributable to garlic of 0.59 mmol/L (95% CI, 0.44 to 0.74) (23 mg/dL [CI, 17 to 29]) (P < 0.001).

Conclusions: Meta-analysis of the controlled trials of garlic to reduce hypercholesterolemia showed a significant reduction in total cholesterol levels. The best available evidence suggests that garlic, in an amount approximating one half to one clove per day, decreased total serum cholesterol levels by about 9% in the groups of patients studied.


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Figure 1.
Effect sizes with 95% CIs for mean improvement during garlic therapy compared with placebo.

Effect size for each trial was computed as the difference between the change of cholesterol level in the garlic and placebo groups. The pooled difference was calculated using data only from homogeneous trials. Any CI that includes zero indicates a nonsignificant result.

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