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There's a widely held belief that garlic enhances immune system. I'll reuse the same links as my earlier "onion" question, but the purported mechanisms seem different, even if they are folded in the same articles:

https://www.webmd.com/food-recipes/features/garlic-immunity-boosting-superstar

https://web.archive.org/web/20191228185524/http://healthfree.com/blog/blog/5-foods-to-naturally-boost-your-immune-system/

https://livewell.jillianmichaels.com/benefits-garlic-onions-5280.html

https://www.naturalnews.com/035462_garlic_immune_boosting_herbs.html

Are there any studies proving or disproving the beneficial effects of the garlic on immune system? (I am specifically interested in resistance to cold/flu viruses, but the claims are frequently more generic.)

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  • I decided to split garlic and onions into separate questions - they are frequently lumped together, but the explanations given actually differ as to the active compounds that are supposed to convey the actual benefit.
    – user5341
    May 25, 2014 at 22:22

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I'll take it that having potent anti-cancer properties means enhancing the immune system. Vegetable extracts have been tried against various tumor lines. In this study Antiproliferative and antioxidant activities of common vegetables: A comparative study from 2009, garlic was found to completely inhibit all tested cell lines. In serial dilution testing

Garlic was the most potent inhibitor of cell proliferation with a marked reduction of U-87 glioblastoma cell proliferation at a 1/1000 (corresponding to 3.32 mg raw vegetable/ml) dilution of the extract.

Garlic and Cancer: A Critical Review of the Epidemiologic Literature says "Evidence from available studies nevertheless suggests a preventive effect of garlic consumption in stomach and colorectal cancers."

Interestingly the commonly consumed western vegetables showed little anti-tumor activity. You can download the paper to read which vegetables did best.

Garlic has also been touted in reducing the occurrence of the common cold. A Cochrane review [2] only found 6 studies, of which only 1 study was of sufficient quality to meet their inclusion criteria. Their conclusion:

There is insufficient clinical trial evidence regarding the effects of garlic in preventing or treating the common cold. A single trial suggested that garlic may prevent occurrences of the common cold but more studies are needed to validate this finding. Claims of effectiveness appear to rely largely on poor-quality evidence.

[2] Lissiman E, Bhasale AL, Cohen M. Garlic for the common cold. Cochrane Database Syst Rev 2012 March 14;3:CD006206. doi: 10.1002/14651858.CD006206.pub3 PubMed PMID: 22419312.

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    Welcome to Skeptics!. There is a huge difference between "inhibits cells in a petri dish" and "works when it is injected in the human body" and "works when ingested in normal amounts by the human body." This study is just a first step toward answering the question.
    – Oddthinking ♦
    May 27, 2014 at 4:07
  • Added another reference.
    – HappySpoon
    May 27, 2014 at 4:30
  • It isn't a strong link, but it is right on target. +1.
    – Oddthinking ♦
    May 27, 2014 at 6:07
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    I'll take it that having potent anti-cancer properties means enhancing the immune system.. I'd say enhancing the immune system does not have a defined meaning, but anyways...
    – nico
    May 27, 2014 at 8:13
  • If you believed that, then you should vote to close the question :)
    – HappySpoon
    May 27, 2014 at 8:54

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