Garlic as a Treatment for High Cholesterol

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The summary below is from the full report titled "Garlic for Treating Hypercholesterolemia. A Meta-Analysis of Randomized Clinical Trials." It is in the 19 September 2000 issue of Annals of Internal Medicine (volume 133, pages 420-429). The authors are C Stevinson, MH Pittler, and E Ernst.

What is the problem and what is known about it so far?

Cholesterol is a type of fat. High blood cholesterol levels are associated with an increased risk for heart disease, stroke, and other circulation problems. High cholesterol levels can be treated with a low-fat diet, exercise, or drugs. Some previous studies have suggested that large amounts of garlic in the diet can also lower cholesterol levels. Many of those studies were small, however, which makes them hard to interpret, and the size of the reduction in cholesterol that can be achieved with garlic is uncertain.

Why did the researchers do this particular study?

To examine the effect of garlic on total cholesterol levels in persons with high cholesterol levels.

What was studied?

Thirteen previously published studies of garlic to treat high cholesterol.

How was the study done?

The researchers used a technique called meta-analysis. This is a statistical method that combines the findings of multiple studies of the same issue into a single result. The researchers exhaustively searched the published literature and contacted experts to identify all studies that had studied the effect of garlic intake on cholesterol levels. The researchers looked for studies in which the study patients had cholesterol levels greater than 200 mg/dL (levels greater than 200 mg/dL are considered "high") and in which patients were randomly assigned to receive a garlic preparation or a placebo. (Placebos looked and tasted like the garlic preparation but contained no active ingredient.) Studies also had to be blinded, which means that neither the patients nor the researchers knew who was getting garlic until the study was completed. Using meta-analysis, the researchers then combined the results from the studies that met their inclusion criteria.

What did the researchers find?

The researchers identified 38 studies that examined the relationship between garlic and lower cholesterol; 13 met their criteria for inclusion. The results of the 13 combined studies indicated that on average, garlic lowered cholesterol 15.7 mg/dL more than placebo did. The researchers judged that 6 studies used the most rigorous research methods; these 6 studies did not show that garlic lowered cholesterol more than placebo did.

What were the limitations of the study?

Using meta-analysis to combine many small studies can be helpful in estimating the effect of a treatment. However, subtle differences among studies, such as differences in the garlic preparations used, may influence the combined results.

What are the implications of the study?

Garlic seems to lower cholesterol more than placebo does. The size of the reduction is small, however, and the results of all studies are not consistent. Using garlic therefore does not seem to be a very effective way to treat high cholesterol.