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Does Eating Garlic Lower Cholesterol?
- Daniel J. Lerner, MD; and
- Stephen B. Hulley, MD, MPH
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TO THE EDITOR:
The recent meta-analysis by Warshafsky [1] concludes that garlic, in an amount approximating one half to one clove per day, decreased total serum cholesterol levels by about 9% in the groups studied. If valid, this could be an important advance, but we have several important concerns.
First, the criteria for including and excluding primary trials were established after the data sere extracted and reviewed. A randomized, double-blind, placebo-controlled trial [2] with 33 patients that showed no cholesterol-lowering effect of garlic was excluded because it did not satisfy a seemingly arbitrary inclusion criterion: a cholesterol level greater than 200 mg/dL in more than 75% of patients.
Second, two other relevant randomized, double-blind, placebo-controlled trials [3] with crossover designs in 85 patients found no difference in serum cholesterol levels between patients in the treatment and placebo arms. The authors excluded these trials because the published report did not contain the initial and final cholesterol values, which are necessary to calculate a difference between groups in the change in cholesterol levels; the missing data should have been obtained.
Third, the sensitivity analysis, which combines eight noncontrolled trials with the five trials used in the primary analysis, assumes that “hypercholesterolemic patients would not improve if left untreated” and uses the pretreatment mean cholesterol levels “as a proxy control for control group performance”. However, a decrease in cholesterol level within a group selected for high initial levels can occur by regression to the mean, even in the absence of intervention, as shown by a trial included in the meta-analysis [4] in which serum cholesterol decreased by 12% in both the treatment and control groups. Thus, the uncontrolled observations in the sensitivity analysis add little to the proposition that garlic is a hypolipidemic agent.
Our final concern is the overall quality of the primary trials. Specifically, we were disturbed that two of the five trials [5, 6] appeared in a journal supplement sponsored by a pharmaceutical company that manufactures garlic extract.
Daniel J. Lerner, MD
Stephen B. Hulley, MD, MPH
University of California at San Francisco; San Francisco, CA 94121
The Editors welcome submissions for possible publication in the Letters section. Authors of letters should:
•Include no more than 300 words of text, three authors, and five references
•Type with double-spacing
•Send three copies of the letter, an authors' form signed by all authors, and a cover letter describing any conflicts of interest related to the contents of the letter.
Letters commenting on an Annals article will be considered if they are received within 6 weeks of the time the article was published. Only some of the letters received can be published. Published letters are edited and may be shortened; tables and figures are included only selectively. Authors will be notified that the letter has been received. If the letter is selected for publication, the author will be notified about 3 weeks before the publication date. Unpublished letters cannot be returned.
Annals welcomes electronically submitted letters.
- Copyright ©2004 by the American College of Physicians
