Some onion varieties can boost anti-cancer benefits, Cornell researchers say

Rui Hai Liu, associate professor of food science, is seen with several onion varieties next to a rotary evaporator, which is used for antioxidant extraction, in his lab in Stocking Hall on Sept. 28. Nicola Kountoupes/University Photography

By Susan S. Lang

Onions are one of those vegetables chock-full of anti-cancer chemicals. However, shallots, Western Yellow, pungent yellow and Northern Red onions are particularly high in these compounds as well as more effective in inhibiting liver and colon cancer cell growth than other common varieties, according to a new study by Cornell food scientists.

Rui Hai Liu, M.D., Ph.D., associate professor of food science at Cornell, led the study to determine the potential health benefits of common onions. He found that Western Yellow, shallots and pungent yellow onions were particularly effective against liver cancer cells, while pungent yellows and Western Yellows had the greatest effect on colon cancer cells.

"Our study of 10 onion varieties and shallots clearly shows that onions and shallots have potent antioxidant and anti-proliferation activities and that the more total phenolic and flavonoid content an onion has, the stronger its antioxidant activity and protective effect," said Liu.

Phenolics and flavonoids are types of phytochemicals, which are antioxidant chemicals that protect plants against bacteria, viruses and fungi. Phenolics and flavonoids, like other antioxidants, help prevent cancer by mopping up cell-damaging free radicals and inhibiting the production of reactive substances that could damage normal cells.

The study of varietal differences in phenolic and flavonoid content and antioxidant activities of onions against cancer cells will be published in the October issue of the Journal of Agricultural and Food Chemistry. It was presented to vegetable growers at the Empire State Fruit and Vegetable Expo in Syracuse in February.

Liu found that shallots had six times the phenolic content than the variety with the lowest content (Vidalia). Western Yellow onions had 11 times more flavonoids than Western Whites, the onion with fewest flavonoids.

Using colon cancer cells treated with extracts from the 10 onion varieties and shallots that were tested, the Liu group found that pungent yellow and Western Yellow onion extracts provided the strongest anti-proliferation protection against colon cancer cells. The Western Yellow, shallots and pungent yellow extracts provided the strongest anti-proliferation protection against liver cancer cells.

"Onions are one of the richest sources of flavonoids in the human diet," Liu pointed out. "And flavonoid consumption has been associated with a reduced risk of cancer, heart disease and diabetes. Flavonoids are not only anti-cancer but also are known to be antibacterial, antiviral, anti-allergenic and anti-inflammatory."

Onions also are the second most important horticultural crop in the world, according to Liu and his co-authors: Jun Yang, a graduate student in food science at Cornell; Katherine J. Meyers, an undergraduate student in food science at Cornell, and Jan Van der Heide of Cornell Cooperative Extension of Oswego County. The retail value of onions in the United States is more than $3 billion. New York state is ranked seventh in total volume of onions produced in the United States, and three of the four of the varieties with the greatest total phenolic and flavonoid content are grown in New York (pungent yellow, Northern Red and shallots).

A number of other studies have found that phytochemicals and antioxidants are the chemicals in fruits and vegetables that could be effective against cardiovascular disease and certain cancers, such as lung cancer, prostate cancer and melanoma cells.

The study was funded in part by the New York State Department of Agriculture and Markets.

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A clarification

Onions grown and marketed under the N.Y. Bold brand name represent only one of the onion production areas of the state. In fact, pungent yellow onions are grown in all onion production areas of the state. Consequently, the results of Liu's research apply to all New York-grown pungent yellow onions, the most commonly grown onion in the state. The research offers all producers of pungent yellow onions in New York state an opportunity to market the healthful attributes of this onion type.

Liu is correcting this error by submitting an erratum to the Journal of Agricultural and Food Chemistry . This is the standard procedure used to address errors that appear in the scientific literature. Likewise, a clarification will appear in the next issue of CALS Connect . The above story and the Cornell News Service release about the study also have been corrected.