Although onions are members of the Allium family of plants, and are close relatives to garlic, they seem to get a lot less attention for their health benefits than their more celebrated botanical cousins.

Nevertheless, onions contain important natural substances for improving health and fighting off chronic disease that should not be overlooked. For example, onions can help you fend off cancer, diabetes, obesity, stroke, Alzheimer’s disease, and Parkinson’s disease.

While you may not think of onions as a cancer fighter, they are. The natural chemicals in onions can help reduce the risk of some of our most common and deadly cancers.

Take colorectal cancers, for instance, which are diagnosed in about 150,000 people a year in the U.S. Statistics show every year, more and more younger people are being diagnosed with this disease – recently there’s been about a one percent annual increase in its incidence in folks under the age of 50.1

A study in Asia compared the diets of more than 800 people with colorectal cancer to folks without the cancer. The researchers found that folks who ate the most onions and other allium vegetables (which include leeks and chives as well as garlic) enjoyed a dramatic reduction in the risk of colorectal cancer– almost 80 percent.2

That’s an astounding result! But onions’ anti-cancer power has been shown in other studies as well.

Superfood Tumor Fighter

When researchers at the University of Guelph in Canada finished researching how onions can help the body resist the formation of tumors, they started referring to onions as a cancer-fighting “superfood.”

The Canadians focused in particular on red onions. Red onions not only contain a high level of quercetin, a flavonoid in all onions that is a well-known antioxidant and inflammation fighter, they also are a rich source of anthocyanin – the pigment that gives red onions their scarlet hue.

The team found that the anthocyanin multiplies the antioxidant power of the quercetin.

In their tests, says researcher Abdulmonem Murayyan, “We found onions are excellent at killing cancer cells. They activate pathways that encourage cancer cells to undergo cell death (apoptosis). They promote an unfavorable environment for cancer cells, and they disrupt communication between cancer cells, which inhibits growth.”

Along with these effects, a study in Japan demonstrates that a compound in onions called onionin A (ONA) can help to inhibit ovarian cancer and lung cancer.

ONA is the Secret Weapon Against Cancer

In these tests, ONA reduced the growth of ovarian tumors by disrupting the tumor-promoting activities of myeloid cells – blood cells that malignant cells commandeer to spread and metastasize.

And ONA produced similar results with lung cancer cells.

The Japanese researchers believe that ONA can potentially be used to improve the cancer-fighting power of cancer drugs and may turn out to be a useful supplement for use by cancer patients.4, 5

Onions have also been shown to help:

  • Lower the risk of osteoarthritis: Research in England has indicated that onions and other allium vegetables can interfere with enzymes in joints that produce arthritic damage to cartilage. They contain a compound called diallyl disulfide that helps keep the joints functioning with less pain.6 
  • Protect the body against obesity, stroke, diabetes, Alzheimer’s disease, and Parkinson’s disease: Onions contain a moderate amount of EGCG, an antioxidant compound that is also found in green tea. In a review of natural foods like onions that contain EGCG, Italian researchers point out that “EGCG is a strong antioxidant and anti-tumor molecule and has the potential to prevent and counteract several human diseases with chronic metabolic and inflammatory components, such as diabetes, stroke, obesity, Parkinson’s, and Alzheimer’s diseases.”7 
  • Lower the risk of blood clots and heart problems: A review study in England uncovered strong evidence that the natural compounds in onions can prevent problematic blood clots.8 And tests in Japan showed that they support improved arterial function.9 

My Takeaway

If you decide to start eating more onions, consuming them in just about any form will get you a serving of natural chemicals that may improve your health. However, deep fried onions may not be a great idea since they will probably contain damaged fats from the frying oil which can trigger many of the diseases onions are said to prevent.

If you enjoy raw onions, the folks at Tufts pointed out that uncooked onions contain healthy compounds that are broken down in the cooking process.10 And the researchers at Guelph have evidence that the pigments in red onions offer some extra benefits. But eating any type of onion as well as other fruits and vegetables is a good bet for improving your health outlook.


  1. https://www.cancer.org/cancer/colon-rectal-cancer/about/key-statistics.html 
  2. https://onlinelibrary.wiley.com/doi/abs/10.1111/ajco.13133 
  3. https://pubmed.ncbi.nlm.nih.gov/28528091/ 
  4. https://pubmed.ncbi.nlm.nih.gov/27393711/ 
  5. https://specialty.mims.com/topic/onionin-a-inhibits-ovarian-cancer-progression 
  6. https://bmcmusculoskeletdisord.biomedcentral.com/articles/10.1186/1471-2474-11-280 
  7. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8247467/ 
  8. https://pubmed.ncbi.nlm.nih.gov/12410539/ 
  9. https://pubmed.ncbi.nlm.nih.gov/23885989/ 
  10. https://www.nutritionletter.tufts.edu/general-nutrition/are-raw-onions-more-nutritious-
    than-cooked-onions/