Strong-flavored onions can be harsh on your social life, but they are potentially great for fighting cancer. Researchers at Cornell University have found in preliminary lab studies that members of the onion family with the strongest flavor -- particularly New York Bold, Western Yellow and shallots -- are the best varieties for inhibiting the growth of liver and colon cancer cells.

"No one knows yet how many daily servings of onions you'd have to eat to maximize protection against cancer, but our study suggests that people who are more health-conscious might want to go with the stronger onions rather than the mild ones," said study leader Rui Hai Liu, MD, PhD, a chemist with Cornell's department of food science in Ithaca, N.Y.

Researchers have known for some time that onions may help fight cancer, but the current study is believed to be the first to compare cancer-fighting abilities among commonly consumed onion varieties. The new study appeared in the November 3, 2004, issue of the Journal of Agricultural and Food Chemistry.

Liu and his associates analyzed 10 common onion varieties and shallots for total antioxidant activity and their ability to fight the growth of cancer in human cell lines. Although shallots resemble onions, they are actually a separate, distinctive species. Fresh, uncooked samples were used, with extracts taken from the bulbs with the outer skin removed.

Shallots and onion varieties with the strongest flavor -- Western Yellow, New York Bold and Northern Red -- had the highest total antioxidant activity, an indication that they may have a stronger ability to destroy charged molecules called free radicals, an excess of which are thought to increase the risk of disease, particularly cancer, the researcher said.

Onion varieties with the mildest flavor -- Empire Sweet, Western White, Peruvian Sweet, Mexico, Texas 1015, Imperial Valley Sweet and Vidalia -- had the lowest total antioxidant activity, Liu said.

In tests against liver and colon cancer cells, onions were significantly better at inhibiting the growth of colon cancer cells than liver cancer cells, an indication that they are potentially better at fighting colon cancer, the researchers said. The strongest cancer-fighters tested were the New York Bold variety, Western Yellow and shallots. The sweetest tasting onions, including the beloved Vidalia, showed relatively little cancer-fighting ability, he noted.

Green onions and cocktail onions were not tested in this study, nor did the researchers test whether cooking made a difference in terms of cancer-fighting ability. Liu cautioned that human studies are needed before any definitive links between onion consumption and cancer prevention can be established.

While popular as fried "rings," onions are known mostly for their ability to add flavor to a variety of food dishes, including meats, pizza, soups and salads. However, they are increasingly becoming known for their potential health benefits. Onions are rich in a flavor compound known as quercetin, a potent antioxidant that has been linked to protection against cataracts and heart disease as well as cancer. They are also sodium-, fat- and cholesterol-free.

Onions are the third-most consumed vegetable crop in the U.S., with a per-capita consumption estimated around 19 pounds per year and a retail value estimated at $3 billion to $4 billion, according to the National Onion Association.