May 15, 2008



Antioxidants are substances that slow or prevent damage to the body’s cells. They protect the cells from unstable molecules known as free radicals, which can increase the effects of aging and the risk of diseases such as cancer and diabetes.

Free radicals are molecules with one or more unpaired electrons. They are a byproduct of a normal bodily process involving the metabolism of oxygen for energy. Environmental factors such as cigarette smoke, air pollution, radiation and ultraviolet light can also cause free radicals to form.

Because free radicals lack an electron, they are unstable and highly reactive. As a result, they steal electrons from other cells, which in turn destabilizes those cells, turning them into free radicals. This chain reaction formation of free radicals can occur indefinitely, causing destruction to the body as cellular damage accumulates.

Antioxidants prevent free radicals from damaging cells by donating electrons to free radicals, thereby stabilizing them. When an antioxidant loses an electron, it remains stable and thus does not itself become a free radical.

There are a number of important substances that supply antioxidants to the body. These include beta-carotene, vitamin C, vitamin E and the mineral selenium.

Fruits and vegetables are the main source of dietary antioxidants. In addition, many foods are fortified with antioxidant vitamins. Antioxidant supplements also are available, but experts generally urge people to avoid them. Research has not revealed whether or not they help prevent disease, and they may be dangerous if taken inappropriately.

About antioxidants

Antioxidants are substances that slow or prevent the oxidation process from damaging the body’s cells. They also repair cell damage, and may improve immune system functioning and lower the risk of infection and cancer.

Antioxidants protect the body from damage caused by unstable molecules known as free radicals. These are molecules that have one or more unpaired electrons. Every cell in the body needs oxygen to produce energy. However, when cells burn oxygen, they create free radicals. Environmental factors such as cigarette smoke, air pollution, radiation and ultraviolet light also can cause free radicals to form in the body.

An unpaired electron makes a free radical unstable and highly reactive. In order to become stable, free radicals seek out and take electrons from body cells. This damages the cells, depriving them of an electron, leaving them unstable and resulting in the formation of another free radical. The new free radical then seeks to take an electron from another cell, creating a chain reaction of free-radical creation that can continue indefinitely.

Occasionally, free radicals are helpful to the body. For example, the immune system may use them to kill disease-causing viruses and bacteria. However, more often, free radicals inflict damage to healthy cells and DNA (which contains the genetic code for human cell reproduction). This can lead to many health problems, including:

  • Age-related deterioration, such as wrinkling of skin
  • Artery and heart disease
  • Cancer
  • Cataracts (clouding of the eye lens)
  • Diabetes

The body’s natural defenses try to limit the damage of free radicals and to repair damaged cells. For example, certain enzymes in the body also work as antioxidants to neutralize harmful substances. However, the effectiveness of this activity is limited and decreases as a person ages.

Antioxidants provide extra help in the body’s fight against free radicals. Antioxidants prevent free radicals from damaging cells by donating electrons to free radicals. When an antioxidant loses an electron, it remains stable and thus does not itself become a free radical. Antioxidants that donate an electron to a free radical neutralize the free radical or convert the molecule into waste to be eliminated by the body. They also may help repair cells already damaged by free radicals.

Much remains to be learned by scientists about antioxidants, and many of the claims made about antioxidants have not yet been conclusively proven. Experts remain unsure of exactly how antioxidants work to help prevent illness.

Scientists believe that antioxidants may protect people from certain diseases (e.g., arthritis, cancer, cataracts, heart disease) and may slow the degenerative process that accompanies aging. For example, studies have shown that people who eat generous amounts of fruits and vegetables (which are high in antioxidants) have lower rates of cancer. However, experts cannot yet definitively say that this is due to the antioxidant content of these foods.

Researchers continue to look for evidence of links between antioxidants and good health. For example, researchers at Ohio State University recently found evidence that combining antioxidant treatment with the use of a certain type of heart drug may help the heart recover better following a heart attack.

Other recent studies have found evidence that antioxidants may:

  • Help slow vision loss caused by eye diseases such as retinitis pigmentosa.
  • Protect against tick-borne illness such as Rocky Mountain spotted fever.
  • Shield the lungs from damage in patients with silicosis, which results from exposure to crystalline silica.

While these studies are promising, they have not yet been confirmed. In addition, other recent studies seem to undermine some of the commonly held assumptions about antioxidants.

For example, researchers at Oregon State University found evidence that flavonoids have little or no value as antioxidants, although they may contain other health benefits.

Types and differences of antioxidants

A handful of food-based substances supply antioxidants to the body. The following are powerful antioxidants found in food:

  • Beta-carotene and other carotenoids. Carotenoids are the pigments in plants that typically cause fruits and vegetables to appear red, orange or deep yellow. Some foods that are dark green also contain carotenoids that are hidden by the green of the plant’s chlorophyll (the chemical that facilitates photosynthesis, the process by which plants convert sunlight into chemical energy). It should be noted that food color is not always a good indicator of antioxidant levels. For example, corn is deep yellow yet does not contain a high level of carotenoids.

    Beta-carotene is the most common carotenoid to appear in foods. It is converted into vitamin A in the body. Other carotenoids found in fruits and vegetables include alpha-carotene, beta-cryptoxanthin, lycopene, lutein and zeaxanthin. Because carotenoids are fat-soluble, they may be stored in the body and help fight free radicals in lipids and fat tissues.

  • Vitamin C. As an antioxidant, vitamin C may protect the body in a fashion similar to beta-carotene. However, vitamin C helps remove free radicals from body fluids (e.g., blood) rather than from fat tissue. It also neutralizes free radicals created from polluted air and cigarette smoke. Research is under way to determine whether vitamin C’s antioxidant properties may help reduce the risk of cancer and cataracts (clouding of the eye lens).

  • Vitamin E. Many health benefits have been claimed on behalf of this vitamin, not all of which have turned out to be true. However, vitamin E does appear to offer many benefits as an antioxidant. It may help to prevent the oxidation of low-density lipoprotein (LDL) cholesterol – the so-called “bad” cholesterol that causes plaque buildup in the arteries – and cell membranes by stopping the free-radical chain reaction process. It also may help prevent some cancers. Vitamin E works together with antioxidants such as vitamin C to prevent other chronic diseases.

  • Selenium. An essential trace mineral in the human body and an important part of antioxidant enzymes that protect against the effects of free radicals. Selenium works with vitamin E to protect cells from damage. The amount of selenium found in foods is directly related to the amount of selenium in the soil in which the food was grown. Some studies indicate that selenium may reduce the risk of cancer, particularly lung, prostate, and colorectal cancers.

Certain enzymes in the body also serve as antioxidants. So do phytonutrients such as flavonoids, which also prevent oxidation of LDL cholesterol, reduce the stickiness of blood platelets and protect against various diseases.

Good sources of antioxidants

Fruits and vegetables are the major source of dietary antioxidants. The highest concentrations are found in the most deeply or brightly colored fruits and vegetables. In addition, many other foods are fortified with antioxidant vitamins. Good sources of various antioxidants include:

  • Vitamin C. Fruits (especially citrus fruits and juices) and vegetables (e.g., green peppers, cabbage, spinach, broccoli, kale, tomatoes)

  • Vitamin E. Apricots, whole grains, nuts, seeds, fish oils, unsaturated vegetable oils, avocado, wheat germ, salad dressings

  • Carotenoids. Liver, egg yolk, milk, butter, and yellow, orange, red and deep-green fruits and vegetables

  • Selenium. Garlic, seeds, Brazil nuts, meat, eggs, poultry, seafood, whole grains (the amount in plant sources varies according to the content of the soil)

  • Lycopene (a type of carotenoid). Tomatoes and tomato products, papaya, apricots, pink grapefruit, blood oranges

  • Flavonoids. Grapes, peanuts, soy, tea, wine

Scientists have developed a measure known as an Oxygen Radical Absorbence Capacity (ORAC) score to determine the antioxidant potential of various foods. The higher the food scores, the greater the likelihood of antioxidant activity and the better at helping to fight disease (e.g., heart disease, cancer). The American Dietetic Association lists several examples, including:


ORAC Units

Prunes (four)


Blueberries (one-half cup)


Blackberries (one-half cup)


Strawberries (one-half cup)


Raisins (one-fourth cup)


Raspberries (one-half cup)


Oranges (one-half cup of sections)


Plums (one)


Red grapes (one-half cup)


Cherries (one-half cup)



ORAC Units

Kale (1 cup)


Beets (one-half cup)


Red bell peppers (one-half cup)


Brussels sprouts (one-half cup)


Corn (one-half cup)


Spinach (1 cup)


Onions (one-half cup)


Broccoli florets (one-half cup)


Eggplant (one-half cup)


Alfalfa sprouts (one-half cup)


Antioxidant supplements also are available, but experts generally urge people to avoid them. There has not been enough research conducted to determine whether or not antioxidant supplements can help prevent disease. People are urged to use extreme caution in taking supplements and to consult a physician before doing so.

Rather than taking supplements, people are urged to eat a well-balanced diet that provides an adequate amount of antioxidants and other nutrients vital to good health. It is important to note that a lack of essential nutrients can damage DNA as much as free radicals.

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