The research team said that red onions were particularly rich in the flavonoid quercetin. Red onions also had significantly high concentrations of anthocyanin, a compound that enhanced the scavenging properties of quercetin against cancer cells. In addition, the scientists said that red onions were equally effective in eliminating breast cancer cells.
"Extracts created from five different Ontario grown onion varieties are effective in inducing cytotoxic, cytostatic, and anti-migratory activities in a human colorectal adenocarcinoma cell line. These extracts significantly induced apoptosis, reduced the rate of proliferation, and slowed the migration of cancer cells into an exclusion zone. Importantly, these effects were at least comparable, and often stronger, than those of the commercially available pure flavonoid compounds.Although positive results were observed at the highest tested concentration (1:10 dilution of onion extracts), the marked success of our crude onion extract supports the notion that dietary supplementation or even the use of a fairly inexpensive onion extract could have potent anti-cancer effects," the researchers explained in an article on Sci-News.com.
"Anthocyanin is instrumental in providing colour to fruits and vegetables so it makes sense that the red onions, which are darkest in colour, would have the most cancer-fighting power...Onions activate pathways that encourage cancer cells to undergo cell death. They promote an unfavourable environment for cancer cells and they disrupt communication between cancer cells, which inhibits growth. The next step will be to test the vegetable’s cancer-fighting powers in human trials," researcher Abdulmonem Murayyan told ScienceDaily.com.
However, outside experts were more skeptical of the study's results. Dr. Justine Alford, senior science information officer at Cancer Research U.K., noted that just because the researchers discovered that extracts from certain onion varieties could eliminate bowel cancer cells in a laboratory stetting does not mean it will have a similar effect on the human body. Dr. Alford also noted that if the scientists are be able to pinpoint the cancer-fighting molecules in onions, then such compounds could be assessed as a possible cancer drug in the future.
The findings were only the latest in a slew of studies demonstrating the powerful anti-cancer properties in onions. In fact, a 1998 study examined eight organosulfur compounds taken from onions and garlic and discovered that the compounds found in both spices offered protective properties against cancer onset. Likewise, a study published in 2001 confirmed that both garlic and onions helped stave off cancer. According to the researchers, the spices' anti-cancer effects were due to the organosulfur compounds that they possessed.
In addition, a study published in 2005 identified seven different flavonoids in southern Italian red onions. The onion variety had relatively high concentrations of the flavonoid quercetin, the research team said. According to the scientists, quercetin helped mitigate the growth and proliferation of breast, colon, endometrial, lung, and prostate cancers. Dr. Rui Hai Liu, an associate professor of food science at Cornell University, also confirmed that onions have some of the highest flavonoid concentrations in the human diet.