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Most Wanted Supplements:

Are They Cancer Killers or Frauds? What You Need to Know

Marketing claims for nutritional supplements can be lofty -- and misleading. What's lurking inside those bottles -- cancer killers? Or con artists?

University of Michigan Comprehensive Cancer Center dietitians Joan Daniels, R.D., and Nancy Burke, R.D., say the best bet for cancer prevention is a healthy diet. Nevertheless, we know many of our patients have questions about supplements. Here's the lowdown on 10 commonly linked to cancer prevention.

Suspect: Fish Oil

Charge: Fish oil contains omega-3 fatty acid, which helps the body absorb nutrients and fend off inflammation. Some studies indicate that omega-3s may prevent cancer and heart disease.

Verdict: Inconclusive.

Like all supplements, researchers don't know whether fish oil acts alone or with other food chemicals to provide cancer protection. Most people can tolerate up to 3,000 milligrams per day of fish oil. But higher doses may impair the immune system and increase bleeding and stroke risk. Instead of using fish oil, include oily fish, such as salmon and tuna, in your diet.

Suspect: Flaxseed

Charge: Flaxseed contains lignans, which may be helpful in reducing cancer risk. Lignans are phytoestrogens, plant chemicals that mimic the hormone estrogen. Flaxseed is also rich in omega-3 fatty acid.

Verdict: Laboratory research has shown flaxseed may slow colon, skin, lung and breast cancer growth, but results haven't been confirmed in humans.

Some people take flaxseed oil, but it does not contain lignans and lacks the antioxidant properties of ground flaxseed. Instead of oil, consider sprinkling ground flaxseed, which is high in fiber and omega-3s, over cereal or yogurt. But use caution: Flaxseed may cause stomach upset. Drink fluids to prevent bowel obstruction. Flaxseed may also interact with blood thinners, including pain medications such as aspirin.

Suspect: Ginger

Charge: Laboratory research at the U-M Cancer Center has shown that ginger may be effective in killing ovarian cancer cells. Ginger is known to control inflammation -- which may play a role in cancer -- and nausea.

Verdict: It's too early to know whether ginger will help treat or prevent cancer.

Ginger supplements are not recommended. However, adding fresh ginger root to your diet or chewing candied ginger for nausea may be helpful. Excessive amounts of ginger should be avoided, as it may interact with blood-thinners and cause lower blood sugar levels in people who take diabetes medications.

Green Tea

Charge: People who drink green tea seem to have a lower cancer risk, particularly for cancers of the bladder, esophagus, ovaries, pancreas and possibly breast. Green tea contains plant chemicals called polyphenols that act as antioxidants and anti-inflammatories.

Verdict: Drinking up to three cups of green tea per day is probably safe for most people and may have anticancer effects.

However, green tea extracts or pills are not recommended. Be aware that green tea contains caffeine, which may interact with medications and keep you awake.

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To make an appointment with a Cancer Center registered dietitian for personalized counseling, call 734-647-8902.

This article first appeared in the Fall, 2009 issue of Thrive. Print the issue.

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