Antioxidants- What we know, What we need to know

Oxidation is a process by which damage occurs as a result of contact with oxygen. Oxidation of iron results in rust, as illustrated by a nail that’s exposed to air. Food spoilage happens, in part, because of exposure to oxygen in the air. Even though oxygen is essential to humans, we aren’t exempt from oxidative damage. We won’t rust or spoil; the damage is more discreet. Oxidation leads to the formation of “free-radicals.” Free radicals form from normal cellular processes. Environmental hazards can increase free radical production. Exposure to the sun’s damaging rays, car exhaust, ozone, cigarette smoke, drugs, poisons, and pesticides can all amplify free radical production. (It’s not enough to take care of ourselves; we must take care of our environment!)

Free radicals are unstable molecules that can damage cells and tissues and can interfere with the immune system. Free radicals are also implicated in heart disease because they favor plaque formation in the arteries, which can lead to atherosclerosis. Free radicals are partially to blame for cataract formation, arthritis, and even the effects of aging.

An antioxidant is a substance that prevents oxidative damage caused by free radicals. Antioxidants hold promise in preventing and treating diseases like cancer and heart disease. The benefits that antioxidants play in diabetes are still unclear and are under study. Certain nutrients have natural antioxidant qualities. Vitamin C, vitamin E, beta-carotene, and selenium all act as antioxidants to protect the body from oxidative damage. Fruits and vegetables are naturally chalk full of antioxidants. To reap the benefits, eat at least 5 servings per day from a combination of fruits and vegetables. (A serving is approximately 1 small piece, or 1/2 cup. The exchange lists can be used for portioning.) Green tea also has antioxidant activity.

Tip: Eat at least five servings per day from a combination of fruits and vegetables.

Recommended Dietary Allowance (RDA): The average daily dietary intake level that’s sufficient to meet the nutrient requirement of nearly all healthy individuals.

Adequate Intake (AI): A recommended intake that’s assumed to be adequate for healthy individuals. This is used when RDAs cannot be determined.

Tolerable Upper Intake Level (UL): The highest level of daily nutrient intake that’s likely to pose no adverse risks for most people.

Vitamin C

Besides acting as an antioxidant, vitamin C has many other useful functions. Among other things, it’s important for wound healing and fighting infections. It also facilitates the absorption of iron; so if you take an iron supplement, eat a food rich in vitamin C at the same time and you’ll absorb the iron better. Vitamin C is a water-soluble vitamin. Some of the vitamin C in foods is lost when the foods are cooked. Steaming or rapid cooking in a small amount of water can help to preserve the vitamin C content of foods. Raw foods contain the maximum amount of vitamin C.

When most people think of vitamin C, they think of orange juice. Sure, oranges are a great source of vitamin C, but so are many other foods.

The following foods are all rich in vitamin C:

Bell peppers

Broccoli

Brussels sprouts

Cantaloupe

Cauliflower

Grapefruit

Greens (cabbage, spinach, collard, turnip, mustard, kale)

Honeydew melon

Kiwi fruit

Mango

Papaya

Potato

Strawberry

Sweet potato

Tangerine

Tomato

Watermelon

Vitamin C Requirements

Recommended Dietary Allowance (RDA) for Vitamin C (in milligrams per day)

Adult women: 75

Pregnant women: 85

Lactating women: 120

Adult men: 90

The Tolerable Upper Intake Level (UL) for all adults is set at 2,000 milligrams per day.

Caution: Supplementation with vitamin C at the upper intake levels may cause upset stomach and diarrhea.

Vitamin E “Tocopherol”

Vitamin E is a fat-soluble vitamin. This vitamin is not lost by most cooking methods, except the high heat of deep-frying. The main function of vitamin E is to serve as an antioxidant. Fruits, vegetables, and grains supply some vitamin E, but salad oils and margarine supply the most. Vitamin E deficiency is very rare.

The following foods provide vitamin E

Almonds

Apricots

Avocado

Corn oil

Green leafy vegetables

Mangos

Margarine

Mayonnaise

Milk

Peanuts

Peas

Salmon

Safflower oil

Soybean oil

Sunflower oil

Wheat germ

Tip: As you probably noticed, many foods rich in vitamin E happen to be high in fat. If you’re trying to lose weight, you shouldn’t eat more fat; instead you may choose to supplement vitamin E.

Vitamin E “Tocopherol” Requirements

Recommended Dietary Allowance (RDA) for Vitamin E (in milligrams per day)

Adult women: 15

Pregnant women: 15

Lactating women: 19

Adult men: 15

The Tolerable Upper Intake Level (UL) for all adults is set at 1,000 milligrams per day.

Tip: Vitamin E is sometimes measured in international units. To convert from milligrams (mg) to international units (IU), multiply by 1.5.

For example: 15 mg = 22 IU, and 19 mg = 28 IU.

Beta-Carotene

Beta-carotene is in the class of nutrients known as carotenoids. There are more than 600 types of carotenoids. Carotenoids, abundant in fruits and vegetables, have antioxidant properties. People who consume diets that are high in fruits and vegetables appear to have less risk for developing certain diseases, including cancer, stroke, and heart disease. Although eating fruits and vegetables has been shown to have health benefits, isolating individual carotenoids and taking them in pill form has not always shown clear-cut health benefits. Supplementation study results range from positive effects to negative health outcomes. Supplementation of carotenoids is not a replacement for eating whole foods.

Beta-carotene’s other important role is that it’s converted to vitamin A in the body. Vitamin A is necessary for vision, healthy skin, fighting infections, reproduction, and normal growth and development. Beta-carotene is a fat-soluble nutrient. Cooking doesn’t destroy it. A very large intake of dietary carotenoids can produce a yellowing of the skin, as avid drinkers of carrot juice can attest!

The following fruits and vegetables are rich in beta-carotene:

Apricots

Asparagus

Broccoli

Cantaloupe

Carrots

Leafy greens (lettuce and all cooked greens)

Mango

Peach

Pink grapefruit

Pumpkin

Red bell peppers

Sweet potato

Tomato

Winter squashes

Beta-Carotene Requirements

No RDAs have been set for beta-carotene. Until more supplementation studies are done to prove safety, carotenoids should be obtained from a healthful intake of fruits and vegetables and not from a pill, unless under medical supervision.

Selenium

Selenium is a trace mineral. Selenium works in partnership with vitamin E to

prevent oxidative damage. The selenium content of food varies according to where it was grown, as soil and water selenium concentrations vary. Selenium deficiency in the United States is very rare.

The following foods are good sources of selenium:

Brazil nuts

Bread

Cereal

Eggs

Fish

Liver

Meats

Pinto beans

Poultry

Shellfish

Soybeans

Sunflower seeds

Tofu

Wheat germ

Whole grains

Selenium Requirements

Recommended Dietary Allowance (RDA) for Selenium (in micrograms per day)

Adult women: 55

Pregnant women: 60

Lactating women: 70

Adult men: 55

The Tolerable Upper Intake Level (UL) for all adults is set at 400 micrograms per day.

Final Tip:

If you aren’t sure whether you should take a vitamin or mineral supplement, you may want to contact a registered dietitian. A registered dietitian can evaluate your diet and your medical history to determine if a supplement could be beneficial. To find a registered dietitian in your area, call 1-800-366-1655.

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SHERRI SHAFER received her BS in Nutrition and Dietetics from the University of California at Berkeley. She has been a Dietitian at UCSF Medical Center for 10 years. Sherri specializes in medical nutrition therapy counseling for individuals in adult and pediatric diabetes clinics, and is an Instructor for classes on diabetes self management for Type 1 and Type 2 diabetes. She has just completed her first book, Diabetes Type 2 Complete Food Management Program from Prima Publishing.