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Some naturopath websites claim that garlic is incredibly good for you:

If garlic had been created in the laboratory instead of by nature, it would probably be a high-priced prescription drug.

The article goes on to claim it prevents cancer, blod clots and infections too.

Is this really true? I'm rather suspicious of that article for a number of reasons, including:

  • The studies it quotes are from the 80's, where it quotes any at all - a lot of the time it just refers to "lots of scientific studies" or "most scientific studies" without referencing anything in particular.
  • If the health benefits were really that irrevocably provable, surely we'd have seen more of a use of the substance by now?

I'm pretty sure that at the very least, the article is exaggerating. But I'm wondering if there are valid medicinal uses for garlic, or such claims are just completely bogus.

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4 Answers 4

up vote 12 down vote accepted

There are many, many claims here. Some are very broad. (e.g. Cancer is not one disease.) I thought the best way to answer is to list some of the properties of garlic that have been subjected to meta-analysis by the Cochrane Collaboration.

Several studies above suggest the side-effects of garlic are not well understood, but they list skin rashes and bad smells. Wikipedia suggests allergies and drug interactions have been reported.

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Good balanced overview - thanks for that! –  berry120 Sep 20 '12 at 14:20
    
So basically, it looks as if there is no clear scientific evidence that eating garlic is benefitial to our heath. I find that intereting, given that I've heard about the miraculous properties of garlic many times before. It's interesting to know they were not based on actual science... –  elbatrofmoc Sep 22 '12 at 16:14
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Of course one clear benefit of garlic is it is very very yummy! –  Sam I Am Oct 19 '12 at 1:19
    
@elbatrofmoc not surprising, as garlic is classed as a food item rather than medicine it probably gets passed over when people look for funding to get new drugs. There's no patent there... –  jwenting Oct 19 '12 at 6:31
    
@jwenting: I am not sure of your point there. If garlic was patentable, these studies would have come out more positive? (Similarly, the original claim complains that if garlic was created in a lab, it would be high-price, which seems to miss the point that if garlic was created in a lab, it would have huge manufacturing costs.) –  Oddthinking Oct 19 '12 at 9:08
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As per Medical Herbalism, "The major odor principle of garlic, allicin is produced from the amino acid alliin by the enzyme alliinase when exposed to air. In both laboratory and clinical studies, allicin has demonstrated antidiabetic, antihypertensive, antibiotic, and hypolipidemic activities. It also enhances fibrinolytic activity in the blood and inhibits platelet aggregation." [1]

Garlic also contains B vitamins, minerals and flavonoids.

This means that therapeutic doses of garlic will indeed have an antimicrobial effect against certain bacteria, viruses, fungi and parasites. What's more, the volatile oil of the garlic gets excreted through the lungs. This makes it especially useful to use for upper respiratory tract infections.

Regarding Cholesterol:

For the cardiovascular system, garlic can be considered a healthy tonic that is preventative against chronic heart diseases. Not only does it lower blood pressure and blood sugar, but it promotes the production of HDL, the good cholesterol, and inhibits LDL, the dangerous lipoprotein. This prevents atherosclerotic build up in the arteries. It is a blood thinner because it lowers the activity of platelet activating factor (PAF) in addition to enhancing the break down of blood clots, which prevents sudden occlusion of arteries and veins.

Hyperlipidemia: There is contradictory evidence about the effects of garlic on cholesterol and triglyceride levels. Initial research in the early 1990s, mostly using a specific garlic powder (Kwai, Lichtwer Pharma) 300 mg three times daily for 12-24 weeks, showed that garlic modestly reduces total cholesterol, low-density lipoprotein (LDL) cholesterol, and triglyceride levels (279,4782,4783,4784,4785,4786,4787,4788). Some evidence also showed that taking very high doses of a specific aged-garlic extract (Kyolic, Wakanuga) 7.2 grams daily for 24 weeks modestly reduces LDL cholesterol (1873,1875). However, many of these trials have serious design flaws and are low-quality studies (4786,4788). Later research has more consistently shown several garlic preparations to be ineffective, including the previously studied specific garlic powder product (Kwai, Lichtwer Pharma) (731,4792,4793,4795,4807), another specific garlic powder product (Garlicin, Nature's Way), an aged garlic extract product (Kyolic-100, Wakanuga), raw garlic (15295), a garlic oil product (Tegra, Hermes) (732), and other garlic preparations (4794,4795,15296). One analysis of garlic studies suggests that garlic might have short-term benefits on lipid levels after 1-3 months of treatment, but no significant benefit after 6 months (6897). Another analysis shows that when the results of all garlic studies are pooled, there appears to be some benefit; however, when only higher-quality studies are analyzed there is no significant benefit (6457). Advise patients with hyperlipidemia that taking garlic supplements is unlikely to provide a clinically significant reduction in cholesterol or triglyceride levels. [3]

The flavonoids are potent antioxidants and therefore protect our bodies against oxidative stress; especially the oxidation of lipids, which when not prevented can lead to atherosclerotic build up in the vasculature as well. In addition, thanks to these antioxidants, "according to epidemiological evidence, garlic may have cancer-preventative properties, especially against cancers of the gastrointestinal tract." [2]

Regarding Blood Pressure:

Hypertension: Some clinical research shows that taking garlic orally can modestly reduce blood pressure in patients with hypertension and in people with normal blood pressure (277,278,279,1873,6897,16605). In one analysis, garlic reduced systolic blood pressure by about 8% and diastolic blood pressure by about 7%, compared to placebo in patients with hypertension (16605). Most studies of garlic for hypertension have used a specific garlic powder formulation (Kwai, Lichtwer Pharma); however, an aged garlic extract has also been used (1873). [4]

[1, 2] Hoffmann, David. Medical Herbalism: The Science and Practice of Herbal Medicine. Rochester, VT: Healing Arts, 2003. Print.

[3,4] http://naturaldatabase.therapeuticresearch.com.libproxy.bridgeport.edu/nd/Search.aspx?cs=&s=ND&pt=100&id=300&fs=ND&searchid=36958136

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Welcome to Skeptics! This reference isn't substantial enough to support all of the claims here. I note that for the first quote, Hoffman, in turn, cites 'Harbourne JB, Baxter H. Phytochemical Dictionary: A Handbook of Bioactive Compounds from Plants. London; Washington, DC: Taylor & Francis, 1993' –  Oddthinking Dec 18 '12 at 13:53
    
Thanks for the welcome :) and indeed you are right! Quite honestly, I assumed that citing the source I had was sufficient, and that if anyone wanted to look into it more (like you, so thanks!) they'd see where they could find additional sources. Stay posted for a more comprehensive response, I'll work on it! –  katvah82 Dec 18 '12 at 21:39
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Although I consider the answer provided by Berry120 a comprehensive one, in addition to it I would like to quote the main conclusions of the review on health benefits of garlic published in the BioMedicine Journal this year (2012).

Does garlic lower cholesterol and reduce blood pressure?

the potent antiinflammatory action of garlic and its sulfur-containing compounds obtained from in vitro and animal studies supports the potential value of garlic in preventing atherogenesis. Evidence indicates that garlic also acts to maintain vascular tone and cardiac function. Experiments on laboratory animals and investigations of humans has proved that diets supplemented with garlic can restore endothelial functions.

Garlic and cancer

Epidemiologically, garlic consumption inversely correlates with the risk of oral, stomach, esophageal, colon, and prostate cancers.

most animal and cell studies suggest that garlic is a potent chemopreventive agent for several types of cancer, acting by inhibiting cell proliferation, arresting the cell cycle, inducing cell apoptosis, and blocking invasion and metastasis.

Garlic and antioxidation

Taken together, these results suggest that garlic has potent antioxidant activity in delaying the onset and development of cardiovascular disease, cancer, diabetes, and neurodegenerative diseases caused by an imbalance between free radical production and antioxidant defense.

General conclusion

The authors of the review acknowledge that most studies which have addressed the protective effect of garlic against cardiovascular disease and cancer were in vitro and animal studies. Importantly, human clinical and intervention studies have been reported to yield inconsistent results. However, the authors point out that the cell studies and the animal studies both seem to support the potential value of garlic in reducing blood pressure, cholesterol, as well as preventing arteriosclerosis and some forms of cancer.

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One of the potential reasons for the confusion from positive, negative and mixed reports available may be due to the simple fact that they may not all be looking at the same thing anyway:

Garlic obviously contains a number of different compounds - concentrations may vary with variety, 'ripeness', harvest conditions.

The compound most often linked to its activity is probably allicin. This compound is not normally present in high concentrations in garlic but is only produced once the enzyme alliinase comes in contact with the allicin precursor aliin. This happens when garlic is crushed or otherwise injured mechanically. Therefore the way garlic is processed may be relevant here.

Even in garlic extract products the release of allicin is problematic (Low allicin release from garlic supplements: a major problem due to the sensitivities of alliinase activity).

In addition allicin is a highly labile compound - chemical and thermostability is relatively low so that alllicin concentrations may change rapidly once produced. The stability also depends on the medium it is in - water and food in general is probably not ideal. It is not clear what the relative activity of the breakdown products and metabolites may be.

A good overview with references can be found here web site Although I have not checked out all the references personally the information broadly reflects other scientific publications.

It has also been suggested that the activity of garlic may actually be related to the presence of a range of compounds which may work together (Intake of garlic and its bioactive components). It is easy to see how this would increase the complexity of the problem of standardisation mentioned above.

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