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Garlic's Cancer Benefits Challenged

Review Suggests Not Enough Evidence for Cutting Risk of Some Cancers
WebMD Health News
Reviewed by Louise Chang, MD

Jan. 6, 2009 -- More research is needed before garlic can be touted as a way to lower the risk of some types of cancer, according to a new review of studies on the issue.

The review shows that despite some health claims to the contrary, there is not enough credible evidence to link garlic to a lower risk of stomach (gastric), breast, lung, or endometrial cancers. But there is some evidence to suggest that the plant may reduce the risk of some other cancers, including cancer of the colon, prostate, ovary, esophagus, larynx, mouth, and kidney.

Many studies have suggested that garlic may reduce cancer risk, but researchers say few of these studies meet the scientific standards to support a health claim according to the FDA's criteria for food labeling.

The new review is published in the January edition of the American Journal of Clinical Nutrition.

Garlic's Health Benefits Hard to Measure

Researchers say it's difficult to evaluate the potential benefits of garlic against cancer for several reasons.

For example, because garlic is intended for use in small quantities as a seasoning, it is very difficult to analyze how much garlic a person consumes based on a questionnaire.

"Moreover, there are too many variables that can affect the chemical composition of garlic, such as the preparation method used (e.g. whether the garlic is raw or cooked, whole or extracted) and the conditions of cultivation," write researchers Ji Yeon Kim and Oran Kwon of the Korea Food and Drug Administration. "For some of these reasons, although this systemic review found many studies on garlic intake and cancer, most of the results indicate that additional studies are needed."

Rating Garlic's Cancer Claims

In the review, Korean researchers evaluated studies on garlic and cancer published between 1955 and 2007.

Of these, 19 human studies met the FDA's scientific standards for evaluation of health claims with respect to food labeling. These standards include using a control group, statistical analysis, and other factors to reduce bias and ensure the accuracy of the findings.

The results of the review found no credible evidence of a link between garlic intake and a reduced risk of stomach, breast, lung, or endometrial cancers.

"However, although very limited, there is credible evidence for an association between garlic intake and colon, prostate, esophageal, larnynx, oral, ovary, and kidney cancers," write the researchers.

Recommended Food Labels for Garlic

On the basis of this review, the researchers recommend the following wording for food labels touting a health benefit of garlic in regard to cancer prevention.

  • Six studies do not show that the intake of garlic reduces the risk of colon cancer but 3 weaker and more limited studies suggest that garlic intake may reduce this risk. On the basis of these studies, it is highly unlikely that garlic intake reduces the risk of colon cancer.
  • Three studies do not show that intake of garlic reduces the risk of prostate cancer, but one weaker, more limited study suggests that intake of garlic may reduce this risk. On the basis of these studies, it is highly uncertain whether garlic intake reduces the risk of prostate cancer.
  • One small study suggests that garlic intake may reduce the risk of esophageal, larynx, oral, ovary and renal cell [kidney] cancers. However, the existence of such a relation between garlic intake and these cancers is highly uncertain.

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