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Top 8 Antioxidants

Antioxidants Prevent Oxidative Stress and Cellular Damage

By Yousry Naguib, Ph.D.

Antioxidants are key players in health. They protect against free radical damage, which occurs when excess chemically-unstable free radicals steal electrons from nearby molecules and cells in order to make up for the ones they lack. This impairs molecular and cellular structures within DNA, protein, and lipids (fats), and can lead to illness. The list associated with free radical excess is long, and includes cancer, arthritis, atherosclerosis, cardiovascular disease, diabetes, AIDS, and Alzheimer's and Parkinson's disease.

Antioxidants help cells cope by scavenging the free radicals and reducing the oxidative stress that they cause. Human blood and tissues contain many different antioxidants that we make all by ourselves. These include superoxide dismutase, catalase, and glutathione peroxidase. Others include copper-binding ceruloplasmin, albumin, iron-binding transferrin, and hemoglobin, uric acid, and bilirubin.

Antioxidants are not always made within the body. Vitamins C and E, some plant chemicals (phytochemicals), carotenoids, and retinoids are natural antioxidants, antioxidants from foods or natural supplements that may significantly increase our arsenal against free-radical induced disorders.


Garlic has been used as a remedy for various ailments since ancient times. But it was not until recently that it was shown to possess antimicrobial, hypoglycemic, hypolipidemic, antitumor, and antiatherosclerotic properties. Some of these properties are attributed to antioxidant effects. For example, in the process of atherosclerosis, free radicals attack the unsaturated fatty acids of low-density lipoprotein (LDL). Macrophages consume the resultant modified LDL and form a foam in the arterial vessels.

Garlic's active chemical constituents, such as allicin, scavenge the free radicals and protect LDL against oxidation. In vivo studies indicate that allicin increases the enzymatic activity of catalase and glutathione, which are two of the antioxidants involved in protecting LDLs and scavenging the free radicals. In a double-blind, placebo-controlled trial, blood LDL in study subjects given 3.6 mg allicin daily for two weeks was found to be significantly less susceptible to copper-induced oxidation than the LDL of the placebo group.

Vitamin C

Vitamin C protects lipids and membranes from oxidative damage by effectively scavenging fat-oxidizing free radicals. It also regenerates free-radical mediated oxidized fat-soluble antioxidants, such as vitamin E. Vitamin C has been found to be important in the prevention of cardiovascular disease and various types of cancer, including bladder, breast, cervical, colorectal, lung, pancreatic, prostate, stomach, leukemia, and non-Hodgkin's lymphoma. A five-year study of Finnish men suggests that vitamin C deficiency may lead to an increased risk of myocardial infarction.

Vitamin C may also help prevent and treat cancer by enhancing the immune system, stimulating collagen formation necessary for "walling off" tumors, and preventing and neutralizing free radicals.

Vitamin E

Vitamin E is the major lipid-soluble antioxidant protecting low-density lipoprotein against free radical-mediated oxidation. (It's actually a generic term for a group of chemicals, the tocopherol and tocotrienol derivatives.)

In a recent randomized, single-blind, placebo-controlled trial, alpha-tocopherol increased LDL resistance to free radical-induced oxidation. Tocotrienols have also proven effective in blocking oxidation of proteins and lipids. In a recent study, gamma- and delta-tocotrienols from palm oil were both able to inhibit human breast cancer growth, and exhibited strong activity against tumor promotion by inhibiting Epstein-Barr virus early antigen.


Most sources of carotenoids are vegetables and fruits. Of all the carotenoids (about 600 are known), alpha-carotene, beta-carotene and cryptoxanthin are the main vitamin A precursors. Most carotenoids have antioxidant activity, particularly against singlet oxygen and oxygen free radicals. Dietary cryptoxanthin increases the resistance to lipid peroxidation in liver homogenate by enhancing the antioxidant efficiency of vitamin E and by providing direct antioxidant activity.

In contrast to epidemiological studies which showed lower risk of cancer among individuals eating fruits and vegetables rich in carotenoids, recent clinical trials indicate that beta-carotene supplements increase the incidence of lung cancer in cigarette smokers. This effect has been attributed to prooxidant action under the considerable oxidative stress of smokers, and beta-carotene was found to increase the natural killer cell activity, particularly in the elderly.

Lycopene, another member of the carotenoid family, is present mostly in tomatoes and is responsible for its red color. Lycopene, in association with alpha-tocopherol, was found to be a potent inhibitor of prostate cancer cell growth.

Lutein and zeaxanthin are carotenoids abundant in the retina of the eye. They are present mostly in the macula, a small portion of the retina at the back of the eye that creates the sharpest vision. Both lutein and zeaxanthin are key components associated with reduced risk for age-related macular degeneration.

Scientists theorize that lutein and zeaxanthin protect the eye by scavenging free radicals produced from harmful ultraviolet radiation. A study found that individuals who consume high amounts of lutein- and zeaxanthin-rich vegetables have a correspondingly reduced risk of developing macular degeneration.


Natural polyphenols include flavonoids, flavonols, isoflavones, procyanidin, anthocyanins and tannins. They are widely distributed in fruits and vegetables. Polyphenols present in grapes, tea, and berries have received especial attention as dietary supplements because of their potent antioxidant activity, which seems to be the basis for their role in preventing heart disease, cancer, and inflammatory conditions. All of these diseases involve free radicals.

Green tea leaves, derived from the plant Camellia sinensis, contain polyphenols, which account for up to one-third of their dry weight. The major polyphenols are epicatechin, epicatechin gallate, epigallocatechin, and epigallocatechin gallate (EGCG). The health benefits of tea polyphenols have been attributed to their antioxidant activity and their ability to scavenge free radicals. Research at the Medical College of Ohio has shown EGCG to prevent cancer by binding to a proteolytic enzyme called urokinase, which is overexpressed in human cancer.

Grape seed and pine bark extracts contain various phenolic compounds including epicatechin, epigallocatechin, ferulic acid, caffeic acid, kaempferol, quercetin, myricetin, and oligomeric polyphenols. These extracts are used in Europe to cure varicose veins and various vascular diseases. They can strengthen fragile blood vessels thus improving capillary and venous circulation.

A double-blind, placebo-controlled study shows that grape seed extracts improve venous functionality and reduce pain and edema. This capillary protective action is due to the free radical scavenging activity of the polyphenols. These polyphenols also enhance plasma antioxidants in plasma, which lowers lipid peroxidation and protects myocardial tissue against ischemic-reperfusion damage.

Grape seed extracts have also been found to be useful in the treatment of a type of retinopathy that causes deteriorating eyesight in diabetics. In a controlled clinical study, people given grape seed extracts for five weeks were better able to tolerate and resist the glare of bright light than the control group. Grape seed extracts are also suggested as a treatment for age-related macular degeneration, and polyphenols in grapes have been shown to spare vitamin C and interact in a cooperative manner with other lipophilic antioxidants such as vitamin E, beta-carotene, and lycopene.

Berries contain significant amounts of polyphenols, which contribute to their antioxidant properties. Cranberries contain mostly anthocyanins and, to a lesser extent, flavonols. Clinical studies have shown cranberry juice to be a potent inhibitor of bacterial adherence in the urinary tract. Other berries have also been shown to possess various biological activities, some of which are associated with the antioxidant properties of their polyphenol content.

Alpha Lipoic Acid

ALA is a versatile antioxidant. It can regenerate both water-soluble antioxidants such as vitamin C and lipid-soluble antioxidants such as vitamin E. ALA is an important cofactor in the mitochondria. ALA is present in red meat, spinach, broccoli, kidney and liver.

Clinically, ALA appears to have the potential to prevent diabetes, lower glucose level, and prevent chronic hyperglycemia associated complications such as neuropathy and cataracts. ALA may also be useful in the treatment of glaucoma, ischemia-reperfusion injury, and cellular oxidative damage. ALA has been used in Germany to treat nerve pain and to partly restore nerve function in diabetics. A clinical study in Germany found significant improvement in the sympathetic system in diabetics after treatment with a high dose of ALA.

Coenzyme Q10 (C0Q10)

CoQ10 is found in virtually all cells of the body and in large amounts in beef heart, pork, sardines, anchovies, salmon, broccoli, spinach, and nuts. It transports electrons in the mitochondria for the generation of energy and helps to prevent and treat various ailments including heart disease, cancer, premature aging, and neurodegenerative disorders.

The reduced form of coQ10 is an effective antioxidant in membranes. In recent research, coQ10 improved heart function and decreased oxidant injury after cardiac ischemia and reperfusion. CoQ10 was also shown to inhibit the formation of the oxidative stress product hydroperoxide in seminal fluid, and therefore may play a therapeutic role in male infertility.


Ginkgo biloba extract is widely used in Europe for alleviating symptoms associated with cognitive disorders. In animal studies, a standardized German ginkgo extract was shown to protect the central nervous system (CNS) and brain and liver mitochondria from oxidative damage. In combination with zinc, it protected the retina from ischemic injury. Brain and CNS cells have high lipid content and therefore are susceptible to free radical attack leading to various disorders, such as Alzheimer's disease.


Antioxidant nutrients tend to work as a team, in a synergetic fashion. These antioxidant nutrients, as well as others not mentioned here, may not have relevant biological activity singly, and they don't work through identical biochemical mechanisms. Together, however, natural antioxidants and those created by the body constitute an interlinked defense system that is protective against diseases associated with oxidative stress.