By Karen Collins, RD
American Institute for Cancer Research

Onions may make your breath stink and garlic may ward of vampires, but more studies link the two vegetables to a lower risk of cancer. However, scientists are still learning how onions and garlic can promote health.

In one study, about 25,000 people from Italy and Switzerland, including some who had recently been diagnosed with cancer were grouped according to how much onion and garlic they routinely ate.

People who used the most onion or garlic were up to 88 percent less likely to have esophagus, mouth, throat, colon, breast, ovary, prostate and kidney cancers than those who said they used little or none. High onion intake, for example, was associated with a 56-percent lower risk of colon cancer and a 25-percent lower risk of breast cancer compared to no onion intake.

As for colon cancer, a study among more than 35,000 women in Iowa found that those who ate one clove of garlic a week had a 32-percent lower risk of the malady than those who ate garlic once a month or less.  An analysis of several studies worldwide linked a 31-percent lower risk of colon cancer with consumption of about four to five cloves of garlic weekly.

Stomach cancer is another of the cancers that research suggests may be reduced by onions and garlic, although the evidence for this association is less clear.

Defeating 'free radicals'

Like many vegetables, onions and garlic contain antioxidants that can block "free radicals" from damaging the DNA in your cells and starting the cancer process. Lab studies on animals have shown that onion and garlic compounds can increase enzymes that deactivate cancer-causing substances in the body.

Furthermore, in the laboratory, onion and garlic compounds slow the growth and stimulate the self-destruction of cancer cells. Given this protective potential, the challenge now is to identify amounts that will provide optimal effects.

Some research hints garlic and onion's protective compounds may work more effectively when combined with other compounds that work differently. For example, animal studies show even greater reduction in cancer development from garlic and tomato than from either alone.

The protective effects of onion and garlic seem related to wherever cancer cells grow in the body and not to any specific tissue, such as breast or thyroid. That leads many scientists to say that although research offers more proof of onion and garlic's impact on some cancers than others, they are likely to offer protection against a wide range of cancers.

Karen Collins is a nationally known registered dietitian and nutritionist whose work appears on Nubella News, MSNBC.com, and other major Web sites. She is nutrition adviser to the American Institute for Cancer Research.

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