Nutrition

Garlic, onion and other Allium vegetables against cancer

Antitumor and cancer-preventive effects of allium vegetables and compounds

Allium is the generic name of a genus^[1] of plants that includes the widely used onion (Allium cepa) and garlic (Allium sativum), as well as approximately 500 other (mostly) wild but also cultivated species and vegetables (leeks, chives [Allium schoenoprasum], scallion, shallot etc.).

While garlic and/or onion have a long history of use for a variety of purposes in traditional and folk medicine^[2] including as a remedy to help prevent former bruises turning malignant, a number of more recent scientific epidemiological and laboratory research studies have been able to show that they and other members of the Allium genus indeed have a protective role regarding the risk of contracting many common cancers.

Allium vegetables are associated with reduced risk of colorectal cancer

In this matched case-control study running over 2 1/2 years and published in the Asia-Pacifc Journal of Clinical Oncology in 2019, the dietary habits of a total of 833 hospitalised colorectal cancer patients were established. Their data was compared to 833 healthy individuals of similar age and living situation (i.e. city or countryside). It was found that both men and women who regularly consumed larger amounts of allium vegetables had a whopping 79 % reduction in their risk of contracting colorectal cancer.
Onion and garlic use and human cancer

Published in the American Journal of Clinical Nutrition in 2006, this "epic"
(very large-scale) study was trying to answer the question whether consumption of onion and garlic had a role to play in the genesis and prevention of various malignancies. Conducted by Italian researchers between 1991 and 2004, the study involved some 30,000 participants (both confirmed cancer patients and healthy controls).

The types of malignancy studied included breast cancer, prostate cancer, ovarian cancer, cancer of the oral cavity and pharynx, colorectal cancer, laryngeal cancer, esophageal cancer, and renal cell (kidney) cancer. Based on food-frequency questionnaires and statistical models adjusted inter alia for calorie intake, results showed a clear inverse association between the frequency of garlic and onion consumption and cancer risk.

This study has been published in its entirety at http://ajcn.nutrition.org/content/84/5/1027.long
Allium vegetables and risk of prostate cancer: a population-based study.

This study, published in the Journal of the National Cancer Institute in 2002, compared the daily consumption of allium vegetables (garlic, onions, chives, scallions, leeks) of 238 prostate cancer patients with that of 471 healthy male controls. Results: Those who ate the most allium vegetables (more than ten grams a day) had a significantly lower prostate cancer risk than those who ate the least (less than 2.2 grams a day).

Interestingly, the researchers found that the reduction in prostate cancer risk linked to the intake of allium vegetables (in this study, majoritarily garlic and scallions) was not dependent on total calorie consumption or what specific diet the men followed.

This study can be read in its entirety at
jnci.oxfordjournals.org/content/94/21/1648.long
Garlic, onion and cereal fibre as protective factors for breast cancer: a French case-control study.

This study (European Journal of Epidemiology, 1998) compared 345 breast cancer patients with the same number of matched healthy controls. Results showed that higher intake of fibre, garlic and onions reduced breast cancer risk.
Spices for Prevention and Treatment of Cancers

Published in Nutrients in 2016, this detailed review includes summaries of a number of studies done on various garlic compounds used on human cancer cell lines or animals^[3]. These studies showed antioxidant, cancer growth-inhibiting and anti-tumor effects, increased apoptosis, enhancement of the immune system, chemo-sensitization (enhanced chemotherapeutic response), and lessened hepatic injury after tamoxifen treatment.

Promising cell line and animal experimentation studies on garlic compounds were done for breast cancer, upper digestive tract and colorectal cancer, leukemia, glioblastoma multiforme, lung cancer, osteosarcoma, pancreatic cancer, bladder cancer, ovarian cancer, and melanoma.

The review also includes research done on cancer-preventive effects of onion (Allium cepa) and scallion (Allium fistulosum).
Aged garlic extract supplementation modifies inflammation and immunity of adults with obesity.

Researchers have become increasingly aware of the role that low-grade inflammation (and inflammation in general) plays in cancer (see e.g. "Cancer-related inflammation" at www.ncbi.nlm.nih.gov/pubmed/18650914) as well as in other chronic disease (cardiovascular, diabetes, depression, obesity, etc.).

This double-blind, placebo-controlled study (published in Clinical Nutrition ESPEN in 2018) showed that regular consumption of aged garlic extract can lower (at least in obese adults) chronic inflammation (as shown in a decrease in inflammatory markers) while improving immune function.

Important tip

As with many fruits and vegetables, nutrients in onions seem to be found most densely packed near the skin. So it may be worth taking the time to peel them thinly, just carefully removing the fibrous outermost parts.

Last but not least

When it comes to cancer prevention, it seems not all onions are created equal — certain types such as pungent yellow and Northern Red onions actually seem to be (even) more effective than others. Western Yellow/pungent yellow onions as well as shallots demonstrated particular effectiveness against liver cancer cells, and the former two varieties also against colon cancer cells.^[4]

Note

If you do a search of the official PubMed biomedical database for the search terms "allium cancer" "garlic cancer" "onion cancer", you will get hundreds of results, among them more studies supporting the anticarcinogenic potential of allium vegetables and/or their constituents including organosulfur compounds, flavonoids (quercetin, fisetin etc.) and selenomethionine.^[5]

Footnotes

1 Genus: a rank in the classification of organisms, below family and above species (en.wiktionary.org/wiki/genus)

2 See e.g. On Garlic’s Health Benefits Against Cancer & Other Diseases.

3 Healing Cancer Naturally does not endorse animal experimentation.

4 See e.g. Onion a day keeps doctor away? Cornell researchers find some onions do indeed have excellent anti-cancer benefits.

5 For instance Allium vegetables in cancer prevention: an overview (2004).

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