To understand more about the latest scientific understanding of antioxidants, such as vitamins C, E and A, and cancer prevention, the Wellness Advisor spoke to Food and Nutrition Expert, Rachel Agnew, RD.
Wellness Advisor: I’ve heard that antioxidants can help with cancer prevention. Is that true?
Rachel Agnew: The ability of antioxidants to destroy or prevent formation of free radicals is what may link them to cancer prevention. Free radicals are a normal occurrence in the body, but if free radicals overwhelm our body’s defenses oxidative stress occurs which leads to cell damage. Factors that can increase free radical production include smoking, pollution, and UV light. Depending on which cell chemicals are damaged by free radicals, such as genes or DNA, the cells may die or become cancerous.
Because oxidative stress is linked to cancer risk, it is possible that antioxidants’ ability to halt oxidative stress could play a role in cancer prevention. Aside from antioxidant activity, antioxidants’ cancer prevention role may also be due to their ability to enhance immune function and possibly prevent the formation of cancer-causing substances, or carcinogens.
The idea that taking vitamins may have an effect on cancer risk is based on studies that found cancer rates to be lower in people who consume diets rich in antioxidants, mainly fruits and vegetables. Lab and animal studies have shown that antioxidants may protect the cell from long-term damage and slow or even prevent cancer development. At this time, the research on antioxidant supplements and cancer prevention for humans remain mixed. Studies are currently underway to help determine the role of antioxidant supplements and cancer prevention in humans.
WA: What does the FDA say about this evidence?
Agnew: The FDA currently states that some scientific evidence suggests that consumption of antioxidant vitamins may reduce the risk of certain forms of cancer. However, FDA does not endorse this claim because the evidence is limited and not conclusive.
WA: Which antioxidants are best suited for cancer prevention?
Agnew: There are a variety of nutrients that have antioxidant activity that may be linked to cancer prevention. Nutrients that combat oxidative stress more commonly include vitamin C, vitamin E, selenium and different carotenoids. These antioxidants, as well as garlic and onions, may also be linked to stomach cancer prevention. In addition to its antioxidant activity, vitamin C is thought to inhibit H. pylori, a compound linked to stomach cancer. The sulfides found in garlic and onions may reduce stomach cancer risk by inhibiting growth of bacteria and strengthening immunity.
Past evidence has linked lycopene, vitamin E, and selenium to prostate cancer prevention. More research is needed to confirm this role. The medical community is currently awaiting the results of a large study further evaluating the role of E and selenium in prostate cancer prevention in healthy men. Some research suggests that people eating lycopene rich diets, mainly tomatoes and tomato products, also have lower risk of lung and stomach cancer.
The carotenoids lutein and zeaxanthin have antioxidant activity and are thought to be potential anti-cancer agents, possibly helping reduce the risk of lung cancer. Studies link low selenium to increased cancer risk. One study found that people taking selenium supplements had fewer cancers of the lung, colon, rectum and prostate.
Polyphenols and EGCG found in green tea may be linked to cancer prevention and various studies indicate a reduced risk of tobacco-related cancers in green tea drinkers. Grapes, grape skin, grape seed extract, and ellagic acid found in berries are all thought to have anti-cancer properties. More research is being done on polyphenols, including flavenoids, to determine their potential role in cancer prevention.
Soy and isoflavones have weak estrogenic roles that may have a potential role in prostate cancer; but the evidence that soy consumption reduces breast cancer risk in adult women remains inconclusive. More research is needed and being done to further evaluate the role and proper doses of certain antioxidants for cancer prevention.
WA: What levels of antioxidants do I need to take to be effective?
Agnew: The Recommended Daily Allowances (RDA) and Upper Limits, set by the Food and Nutrition Board of the Institute of Medicine, are available for some of the antioxidants mentioned including vitamin E, vitamin C, and selenium. The RDA’s are set for and targeted toward healthy adults in order to maintain adequate nutrient levels and prevent deficiencies. Although higher doses are generally recommended for therapeutic and preventive purposes, exceeding the Upper Limits is not recommended unless under the supervision of your healthcare provider. For those nutrients without RDA’s, it is best to follow the dose recommendations on the label or those of your healthcare provider. For individualized dose and supplement recommendations, see a nutritionally oriented physician or a registered dietitian.
WA: What other steps should I take to lessen the risk of cancer?
Agnew: Most experts agree that eating a healthy diet and maintaining a healthy weight are the best ways to lower cancer risk. Some scientists estimate that people can reduce their risk of cancer by 30%-40% by eating more fruits, vegetables, and other plant sources. Although some supplements may have preventative properties for certain disease states, vitamin/mineral supplements do not replace the need to eat a healthy diet, exercise, and maintain a healthy body weight.
