An antioxidant is a chemical that prevents the oxidation of other chemicals. In biological systems, the normal processes of oxidation (plus a minor contribution from ionizing radiation) produce highly reactive free radicals. These can readily react with and damage other molecules: in some cases the body uses this to fight infection. In other cases, the damage may be to the body's own cells. The presence of extremely easily oxidisable compounds in the system can "mop up" free radicals before they damage other essential molecules.

Virtually all studies of mammals have concluded that a restricted calorie diet extends the lifespan of mammals by as much as 100%. This remarkable finding suggests that food is actually more damaging than smoking which takes on average 25% of a person's lifespan. As food produces free radicals (oxidants) when metabolized, antioxidant-rich diets are thought to stave off the effects of aging significantly better than antioxidant poor diets. This is thought to be a significant explanatory factor (but not the only reason) for the success of caloric restriction.

Types of antioxidants
The following vitamins have shown positive antioxidant effects:

Vitamin A (Retinol, also synthesized by the body from beta-carotene) protects dark green, yellow and orange vegetables and fruits from solar radiation damage, and is thought to play a similar role in the human body. Carrots, squash, broccoli, sweet potatoes, tomatoes (red because of lycopene, kale, collards, cantaloupe, peaches and apricots are particularly rich sources of beta-carotene.
Vitamin C (Ascorbic acid) is a water-soluble compound that fulfills several roles in living systems. Important sources include citrus fruits (such as oranges, sweet lime, etc.), green peppers, broccoli, green leafy vegetables, strawberries, raw cabbage and tomatoes. Linus Pauling was a major advocate for its use.
Vitamin E, including Tocotrienol and Tocopherol, is fat soluble and protects lipids. Sources include wheat germ, nuts, seeds, whole grains, green leafy vegetables, vegetable oil, and Fish Liver Oil. Recent studies showed that some tocotrienol isomers have wonderful anti-oxidant properties.
Selenium must be taken in measured amounts because large doses of the element can be toxic. Good food sources include fish, shellfish, red meat, grains, eggs, sunflower seeds, chicken, Garlic, and brazil nuts. Vegetables can also be a good source if they are grown in selenium-rich soils. Some nutritional supplements contain beneficial amounts of Selenium, but the total intake must be regulated to avoid toxicity. Workers in Integrated Circuit fabrication have been known to develop toxic levels of Selenium through contact with chemicals used in industrial processes.
Special note: Omega 3 fatty acids prevent the formation of atherosclerosis when they are taken in conjunction with antioxidants to prevent themselves being oxidised.

More Books about Antioxidants

A wide variety of antioxidants occur naturally in the body; many of these are enzymes such as glutathione peroxidase, superoxide dismutase and catalase. Bilirubin, a breakdown product of blood, has been identified [1] as a possibly significant antioxidant.

Free radical damage in living cells mitochondria is a byproduct of oxidative phosphorylation. Superoxide radicals are generated, which can damage mitochodrial DNA and mitochondrial membranes. Unlike DNA in the cell nucleus, mitochondrial DNA has only a few DNA-repair enzymes and the DNA is not protected by histones.

Many antioxidants, however (including vitamin C and vitamin E) can't get into mitochondria for various reasons (e.g. because too hydrophilic to cross mitochondrial membranes or too hydrophobic to cross the cytoplasm). A group of scientists in Russia (led by V. Skulachev) have created a custom antioxidant (a Skulachev ion forms the point of the molecule and penetrates the mitochondrial membrane; the antioxidising part is attached behind it) that can enter the mitochondria and stays there due to the membrane potential gradient; preventing damage to DNA.

Tests dating back to the 1950's have indicated that nutritional supplementation of trace amounts of the mineral Selenium is highly beneficial in reducing the actual occurrence, as well as prevention of male prostate cancer. Recent studies conducted using modern statistical methods by the China national health system have verified these earlier studies.

Although there is little doubt that antioxidants are a necessary component for good health, there is considerable doubt as to the most beneficial antioxidant(s) and as to the optimal amount for results. A study of lung cancer patients found that those given antioxidant supplements had worse prognoses. This is believed to be due to antioxidant interference with the body's normal use of localised free radicals e.g. Nitric oxide for cell signalling. Due to the complex nature of the interactions of antioxidants with the body, it is difficult to interpret the results of many experiments designed to test such things. In vitro testing (outside the body) has shown many natural antioxidants, in specific concentration, can halt the growth of or even kill cancerous cells.

For example, recent studies are suggesting that at high levels, synthetic antioxidant vitamins such as A, E and C may prove to have pro-oxidant effects: increasing the formation of free radicals. The fact that natural antioxidants are always ingested together with a wide variety of flavonoids and other phytochemicals also likely plays a part. Many supplement manufacturers supply more expensive tablets containing these. Newer liquid nutritional supplements using plant ionic compounds are believed to be more readily absorbed in the human body.

The benefits of antioxidants were examined during the Age-Related Eye Disease Study.

Commercial antioxidants
Many nutraceutical and health food companies have, in light of scientific studies, produced products that supplement the diet with such antioxidants. Large companies such as the Nutraceutical Corporation and Natrol have products that are explicitly composed of derivatives that contain antioxidants, like resveratrol in grape seeds. Other companies, such as Canprev, Vemma and Natural Health, produce supplements that contain a combination of antioxidants, like their Immunotality formula.

Specialty herbs such as Green Tea and jiaogulan, with makers like Japanese Green Tea and Arizona (for iced) have benefitted tremendously from recent articles on antioxidants in green tea delaying onset of AMD.
The source of this article is Wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL
 

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