Free-Radical Thinking
December 1998 -- Nutrition Notes

By: Andrea Platzman, R.D.
Contributing Editor

  It's not just your mom insisting you eat your fruit and vegetables, but a network of scientists, physicians, dietitians and even chefs.  Current research shows that certain antioxidant nutrients found in these foods, especially vitamins C and E, can neutralize free radicals. An antioxidant is a synthetic chemical (such as BHA or BHT) or another agent (plant- or animal food component) that reduces the damage caused by free radicals. A free radical is a compound with an extra electron. Free radicals are unstable and react readily with other molecules, forming long chains of free radicals.  These free radicals can react with unsaturated fatty acids, proteins and DNA, damaging them. One theory is that they damage the DNA molecules, creating cancer. Another theory - the oxidative stress theory - states that if the body exceeds the antioxidant level necessary to avoid oxidation, the result is too many pro-oxidants. The result: cancers, heart disease and stroke.Super cell protectors  Antioxidants can be broken down into nutritive antioxidants and non-nutritive antioxidants. "Nutritive antioxidants include vitamins C, E, carotenoids and selenium, and there are RDAs for these antioxidants," says Paul Lachance, Ph.D., C.N.C., executive director, the Nutraceuticals Institute, Rutgers University, New Brunswick, NJ.  "Non-nutritive antioxidants include a whole array of nutraceuticals, phytochemicals - and there aren't RDAs for these antioxidants," he explains. "For example, for carotenoids, there are over 600 in nature and 300 in the food system - all different. Lycopene and lutein are examples of non-nutritive antioxidants."  It doesn't take much to meet the modest Recommended Dietary Allowance (RDA) for vitamin C of 60 mg, the amount needed to ward off scurvy. Recent evidence shows that vitamin C might help prevent cardiovascular disease by improving cholesterol levels. Several studies have found that people with high vitamin C levels in their blood tend to have higher levels of high-density lipoprotein ("good cholesterol") compared to people with low levels of the vitamin. Additionally, vitamin C also might keep low-density lipoprotein ("bad cholesterol") from turning bad in the first place. Low-density lipoprotein promotes clogged arteries only when its molecular structure has been oxidized or damaged by free radicals. Vitamin C acts as an antioxidant to disarm the free radicals before they do any harm.  Vitamin C also might help to block the body's cells from turning cancerous. However, in a study published in the April 9, 1998, issue of the British journal Nature - "Vitamin C Exhibits Pro-oxidant Properties" - researchers concluded that taking more than 500 mg of vitamin C daily could cause the vitamin to act as a pro-oxidant, possibly damaging adenine bases in DNA. This might lead to some cancers and arthritis. Several researchers dismissed the study as inconclusive, still maintaining that vitamin C's benefits outweigh any possible negative effects, and that it is safe in common dosages of 1,000 to 2,000 mg daily. Vitamin C replenishes and restores vitamin E, so that this important vitamin can act as an antioxidant.  The human body's most important antioxidant is d-l alpha-tocopherol. Vitamin E might play a role in preventing heart disease by slowing the oxidation of low-density lipoproteins by free radicals, making cholesterol less likely to clog coronary arteries. Vitamin E may help reduce the risk of certain cancers - including breast, lung, prostate, mouth and stomach - by preventing the damage to DNA that initiates the cancer process. Good results have been obtained in studies using 200 to 800 IUs of this vitamin. Similar to the tocopherols, tocotrienols (a lesser known form of vitamin E) also act as antioxidants. Tocotrienols are found naturally in some whole grains and in palm oil. They might lower cholesterol levels as well as prevent certain cancers.  Beta-carotene is just one of the 600 colorful pigments belonging to the carotenoid family. Not all carotenoids are alike. Beta-carotene is one of the carotenoids that can be converted into vitamin A, providing 25% of this vitamin in the diet. Research still is being conducted on the antioxidant ability of beta-carotene and other carotenoids. Beta-carotene supplements were extremely popular until between 1994 and 1996, when some studies determined they provided no health benefit; two studies even suggested they could harm smokers.  The enzyme glutathione eliminates compounds that can contribute to free-radical formation. Selenium is important because it's the active part of glutathione. Recent research has shown that a 200 µg dose daily might prevent prostate, lung and colon cancers. However, more than 800 µg can cause diarrhea, brittle nails and thinning hair, and even more can kill. Reproducible research is needed and studies are currently under way.  A newly recognized antioxidant, alpha-lipoic acid, not only protects against free-radical damage, but also enhances the action of vitamins C and E. Alpha-lipoic acid is found in small amounts in the body and in all living things. Inside the cells it helps to convert sugars into energy. Dosages ranging from 100 to 1,200 mg daily have been shown to ease nerve pain or numbness due to diabetes.Food or supplement?  Only 27% of the population eats the recommended five-a-day servings of fruit and vegetables. However, it's not known what they're eating - is it five bananas or a variety of fruit and vegetables? In addition, those maintaining a low-fat diet can find it extremely difficult to get the recommended dosage of vitamin E. "The RDAs are not enough," Lachance explains. "They do not prevent chronic disease. Taking antioxidants beginning in your teens, so your body can build up a good defense, is a good idea. You can get all of the necessary antioxidants by food alone.  "However, rarely does someone select their fruit and vegetables based on their antioxidant content," he says. "It is recommended to take a standard supplement as well as consume foods containing these antioxidants, so you get the whole array of phytochemicals as found in nature."  Andrea D. Platzman is a registered dietitian who is a consultant to the food industry, and regularly writes for nutrition publications. She earned a master's degree in nutrition from New York University, and has a culinary and business background.Back to top