Abundant in vegetables, whole grains, and fruits, antioxidants are naturally occurring nutrients that neutralize harmful, unstable molecules in the body called free radicals. Research shows that free radicals may be responsible for cancer, heart disease, respiratory ailments, and the aging process itself. By protecting the immune system and repairing damage inflicted by free radicals, antioxidants (also known as "free radical scavengers") may help prevent disease and early aging.
Free radicals are constantly present in the body, formed by the myriad chemical reactions that occur daily and by exposure to various factors. These include ultraviolet radiation, cigarette smoke, rancid fat, polyunsaturated fats, chronic inflammation, herbicides, and pollution. Free radicals steal nearby stable molecules' electrons to complete their own molecular structures, thus destabilizing the target molecule. This causes a lightning-fast chain reaction that produces many more free radicals, resulting in what is clinically known as oxidative stress. Many scientists believe that this stress leads to disease and premature aging if an organism has insufficient antioxidants on hand to stop the reaction.
The medical community as a whole generally agrees that antioxidants are more effective when consumed in the form of 5-8 daily servings of fruits and vegetables than as supplements, although some studies indicate that higher intake can benefit people with known illnesses. Some of the substances can even be toxic when taken in excessive doses. Indeed, it may be that other chemicals found in antioxidants' natural sources are responsible for the beneficial effects presently associated with antioxidants-- scientists are still investigating the matter. In the meantime, a heated debate continues over the most appropriate doses of these nutrients for humans.
The main recognized antioxidants are the carotenoids (precursors of vitamin A), vitamin C (ascorbic acid), and vitamin E (tocopherol). Beta-carotene, lutein, and lycopene comprise the carotenoid antioxidants. They occur naturally in such foods as dark-green leafy vegetables and orange, yellow, and red foods, such as yams and carrots. Lending credence to the widespread belief in this antioxidant's power to slow the aging process, some clinical studies have shown that the carotenoid level in a mammal's tissues is an effective predictor of its life span.
Vitamin C, the most plentiful water-soluble antioxidant, is present in all citrus fruits and such vegetables as broccoli, sweet peppers, and potatoes. This vitamin has often been associated with reduced rates of all kinds of cancer, but especially those affecting the larynx, esophagus, and mouth. Vitamin C is also important for its ability to recycle vitamin E after the latter neutralizes a free radical. Studies have indicated that it may be particularly effective in combating the free radicals generated by smoking and pollution.
Vitamin E, the most plentiful fat-soluble antioxidant, is a component of some oil-containing foods, such as peanut butter, seeds, vegetable oils, and whole grains. It may offer significant protection against cardiovascular diseases by fighting oxidation of LDL (low-density lipoprotein) cholesterol and preventing the buildup of arterial plaque. Some scientists believe vitamin E is the most powerful antioxidant. In the late 1990s, small studies suggested that the vitamin may provide some protection against Alzheimer's disease by preventing the brain's frontal and temporal lobes from falling prey to free radical damage.
Researchers have identified many other natural antioxidants, including the trace minerals selenium, manganese, and copper (which work in conjunction with enzymes); flavonoids (plant pigments such as those found in milk thistle and gingko biloba); and amino acids containing sulfur (methionine and cysteine, which are present in beans, eggs, nuts, brewer's yeast, liver, and fish). More recently, researchers have identified antioxidants in such substances as green tea (polyphenols), grapes (ellagic acid), seeds and nuts (coumarines), and blueberries and peaches (chlorogenic acid). In addition, the human body produces its own antioxidants that take the form of enzymes, including catalase, glutathione peroxidase, and superoxide dismutase.
Each of these neutralizes a specific kind of oxidation. Some antioxidants—for example, butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), propyl gallate, ethylenediamine tetraacetic acid (EDTA), and tert butylhydroquinone (TBHQ)--are also commonly used as food additives to slow fat spoilage and prevent color changes. They work by serving as a decoy for a product's fat, since atmospheric oxygen prefers to react with the antioxidants instead of oxidizing the fat. However, several studies have suggested that these food-preserving antioxidants may in fact be carcinogenic or cause mild to life-threatening allergies.
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