The term “antioxidant” refers to the activity possessed by numerous vitamins, minerals and other phytochemicals to serve as protection against the damaging effects of highly reactive molecules known as free radicals. Free radicals have the ability to chemically react with, and damage, many structures in the body. Particularly susceptible to oxidative damage are the cellular membranes, mitochondrial membranes, and DNA of virtually all cells. Free radical reactions and oxidative damage have been linked to many of the “diseases of aging” such as heart disease and cancer. Antioxidant dietary supplements are routinely marketed with direct and implied claims for cellular protection, anti-aging effects, prevention of cancer and heart disease, reduction of wrinkles, enhancement of immune function, and prmotion of vision and eyesight.
The free radical theory of aging (and disease promotion) holds that through a gradual accumulation of microscopic damage to our cell membranes, DNA, tissue structures and enzyme systems, we begin to lose function and are predisposed to disease. In response to free radical exposure, the body increases its production of endogenous antioxidant enzymes (glutathione peroxidase, catalase, superoxide dismutase), but it has been theorized that supplemental levels of dietary antioxidants may be warranted in some situations to help prevent excessive oxidative damage to muscles, mitochondria and other tissues (such as during/following intense exercise and exposure to pollutants such as second hand smoke and oxidizing radiation such as sunlight).
The 4 key nutritional antioxidants, vitamins C and E, beta-carotene and selenium, are well studied, relatively inexpensive, and widely available as dietary supplements. There are also a multitude of fruit and vegetable phytonutrient extracts that also possess significant antioxidant activity. In most cases, phytonutrient extracts tend to be quite expensive, although their potent antioxidant activity may allow dosages to be fairly small. Some of the more popular antioxidant nutrients found in commercial dietary supplements also include Zinc, Copper, Ginkgo biloba extract, Grape seed extract , Pine bark extract, Lycopene, Lutein, Quercetin, and Alpha lipoic acid as well as dozens of others.
When it comes to antioxidant supplementation, it is the overall collection of several antioxidants that is important (rather than any single “super” antioxidant). This concept of balancing supplemental antioxidants is referred to as the “Antioxidant Network.” and is generally comprised of 5 major classes of antioxidants: Carotenoids, Tocopherols/Tocotrienols (Vitamin E), Vitamin C, Thiols (e.g. sulfur-containing compounds such as alpha-lipoic acid and cysteine), and Bioflavonoids. In theory, smaller doses of these antioxidant agents, when given in combination, will help to regenerate one another following free radical quenching – thus delivering a more effective and safer antioxidant regimen than with higher doses of isolated antioxidant nutrients. This combined approach to antioxidant supplementation is also logical because certain antioxidants will work primarily against certain free radicals and in specific parts of the body (e.g. vitamin E against hydroxyl radicals and within cell membranes or vitamin C against superoxide and within aqueous spaces).
Thousands of studies have clearly documented the beneficial effects of dozens of antioxidant nutrients – and there are thousands of nutrients and phytochemicals that possess significant antioxidant activity in the test tube. Increased dietary intake of antioxidant nutrients, such as vitamins C and E, minerals such as selenium and various phytonutrients such as extracts from grape seed, pine bark and green tea have all been linked to reduced rates of oxidative damage and may help reduce the incidence of chronic diseases such as heart disease and cancer. Readers are referred to the specific sections dealing with each antioxidant nutrient for a full discussion of the pros and cons of supplementation with a given nutrient.
Safety / Dosage
At the typically recommended levels, the majority of antioxidants appear to be quite safe. For example, vitamin E, one of the most powerful membrane-bound antioxidants, also has one of the best safety profiles. Doses of 100-400 IU of vitamin E have been linked to significant cardiovascular benefits with no side effects. Vitamin C, another powerful antioxidant, can help to protect and restore the antioxidant activity of vitamin E, and is considered safe up to doses of 500-1,000mg. Higher doses of vitamin C are not recommended because of concerns that such levels may cause an “unbalancing” of the oxidative systems and actually promote oxidative damage instead of preventing it. Another popular antioxidant, beta-carotene, is somewhat controversial as a dietary supplement. Although diets high in fruits and vegetables deliver approximately 5-6 mg of carotenes daily, these would be a mixture of beta-carotene and other naturally occurring carotenoids. Concern was raised several years ago by studies in which high dose beta-carotene supplements appeared to promote lung cancer in heavy smokers. Those studies provided beta-carotene supplements of 20-60mg/day – about 5-10 times the levels that could reasonably be expected in the diet.
Based on the available scientific evidence, daily supplementation with Vitamin E (100 to 400 IU), Vitamin C (250 to 1,000mg), Beta-carotene (5 to 6mg), and Selenium (70 to 200mcg) appears to be prudent.
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EDITOR'S NOTE: This monograph can be found in The Health Professional's Guide to Dietary Supplements (Lippincott, Williams & Wilkins) by Shawn M. Talbott, PhD and Kerry Hughes, MS.