Only 1 study in Israel showed a marked reduction in coronary heart disease among people with type 2 diabetes. A beta-carotene study showed that the antioxidant provided no protection against heart disease or stroke. A study of vitamin and mineral supplements vitamin C, vitamin E, beta-carotene, selenium, and zinc showed no decrease in overall rates of cardiovascular disease. Unfortunately, few trials have gone on long enough to show a benefit in cancer patients.
Several beta-carotene trials have shown no benefit on cancer. The one bright spot for antioxidant vitamins is a trial where patients taking vitamin C, beta-carotene, and zinc received some protection from antioxidants against the development of advanced age-related macular degeneration, but not cataracts.
But antioxidants continue to be added to breakfast cereals, energy bars, sodas, sports drinks, and other processed foods. Often claims have stretched and distorted data. January 14, Charles H. Patients may have questions about taking antioxidants. What Are Free Radicals? What Are Antioxidants?
Does Research Support Use of Antioxidants? Cancer Unfortunately, few trials have gone on long enough to show a benefit in cancer patients. References The Nutrition Source.
Antioxidants: beyond the hype. This reaction leads to the formation of malondialdehyde MDA and conjugated diene compounds, which are cytotoxic and mutagenic. Lipid peroxidation occurs by a radical chain reaction, i. If not regulated properly, oxidative stress can induce a variety of chronic and degenerative diseases as well as the aging process and some acute pathologies trauma, stroke.
The development of cancer in humans is a complex process including cellular and molecular changes mediated by diverse endogenous and exogenous stimuli. It is well established that oxidative DNA damage is responsible for cancer development.
Cancer initiation and promotion are associated with chromosomal defects and oncogene activation induced by free radicals. A common form of damage is the formation of hydroxyled bases of DNA, which are considered an important event in chemical carcinogenesis 3 , 9.
This adduct formation interferes with normal cell growth by causing genetic mutations and altering normal gene transcription. Oxidative DNA damage also produces a multiplicity of modifications in the DNA structure including base and sugar lesions, strand breaks, DNA-protein cross-links and base-free sites.
For example, tobacco smoking and chronic inflammation resulting from noninfectious diseases like asbestos are sources of oxidative DNA damage that can contribute to the development of lung cancer and other tumors 3 , 6. The highly significant correlation between consumption of fats and death rates from leukemia and breast, ovary, rectum cancers among elderly people may be a reflection of greater lipid peroxidation 5 , Cardiovascular disease CVD is of multifactorial etiology associated with a variety of risk factors for its development including hypercholesterolaemia, hypertension, smoking, diabetes, poor diet, stress and physical inactivity amongst others 2 , 15 , Recently, research data has raised a passionate debate as to whether oxidative stress is a primary or secondary cause of many cardiovascular diseases Further in vivo and ex vivo studies have provided precious evidence supporting the role of oxidative stress in a number of CVDs such as atherosclerosis, ischemia, hypertension, cardiomyopathy, cardiac hypertrophy and congestive heart failure 2 , 5 , 15 , There is now substantial evidence that inflammatory lung diseases such as asthma and chronic obstructive pulmonary disease COPD are characterized by systemic and local chronic inflammation and oxidative stress 21 - Oxidants may play a role in enhancing inflammation through the activation of different kinases and redox transcription factors such as NF-kappa B and AP-1 23 , Rheumatoid arthritis is an autoimmune disease characterized by chronic inflammation of the joints and tissue around the joints with infiltration of macrophages and activated T cells 4 , 25 , Oxidative damage and inflammation in various rheumatic diseases were proved by increased levels of isoprostanes and prostaglandins in serum and synovial fluid compared to controls Oxidative stress plays a role in a variety of renal diseases such as glomerulonephritis and tubulointerstitial nephritis, chronic renal failure, proteinuria, uremia 5 , The nephrotoxicity of certain drugs such as cyclosporine, tacrolimus FK , gentamycin, bleomycin, vinblastine, is mainly due to oxidative stress via lipid peroxidation 27 - Heavy metals Cd, Hg, Pb, As and transition metals Fe, Cu, Co, Cr -induced different forms of nephropathy and carcinogenicity are strong free radical inducers in the body 11 , Oxidative stress is implicated in age-related macular degeneration and cataracts by altering various cell types in the eye either photochemically or nonphotochemically Under the action of free radicals, the crystalline proteins in the lens can cross-link and aggregate, leading to the formation of cataracts In the retina, long-term exposure to radiation can inhibit mitosis in the retinal pigment epithelium and choroids, damage the photoreceptor outer segments, and has been associated with lipid peroxidation Oxidative stress is involved in many mechanisms in the development of fetal growth restriction and pre-eclampsia in prenatal medicine 34 - In pregnancies complicated by pre-eclampsia, increased expression of NADPH oxidase 1 and 5 isoforms which are the major enzymatic sources of superoxide in the placenta is seen The body has several mechanisms to counteract oxidative stress by producing antioxidants, either naturally generated in situ endogenous antioxidants , or externally supplied through foods exogenous antioxidants.
The roles of antioxidants are to neutralize the excess of free radicals, to protect the cells against their toxic effects and to contribute to disease prevention. Endogenous compounds in cells can be classified as enzymatic antioxidants and non-enzymatic antioxidants.
Besides hydrogen peroxide, GPx also reduces lipid or nonlipid hydroperoxides while oxidizing glutathione GSH 2 , 5 - The non-enzymatic antioxidants are also divided into metabolic antioxidants and nutrient antioxidants. Metabolic antioxidants belonging to endogenous antioxidants, are produced by metabolism in the body, such as lipoid acid, glutathione, L-ariginine, coenzyme Q10, melatonin, uric acid, bilirubin, metal-chelating proteins, transferrin, etc 5 , 6. While nutrient antioxidants belonging to exogenous antioxidants, are compounds which cannot be produced in the body and must be provided through foods or supplements, such as vitamin E, vitamin C, carotenoids, trace metals selenium, manganese, zinc , flavonoids, omega-3 and omega-6 fatty acids, etc.
When an antioxidant destroys a free radical, this antioxidant itself becomes oxidized. Therefore, the antioxidant resources must be constantly restored in the body. Thus, while in one particular system an antioxidant is effective against free radicals, in other systems the same antioxidant could become ineffective.
Also, in certain circumstances, an antioxidant may even act as a pro-oxidant e. The antioxidant process can function in one of two ways: chain-breaking or prevention.
For the chain-breaking, when a radical releases or steals an electron, a second radical is formed. The last one exerts the same action on another molecule and continues until either the free radical formed is stabilized by a chain-breaking antioxidant vitamin C, E, carotenoids, etc , or it simply disintegrates into an inoffensive product.
The classic example of such a chain reaction is lipid peroxidation. For the preventive way, an antioxidant enzyme like superoxide dismutase, catalase and glutathione peroxidase can prevent oxidation by reducing the rate of chain initiation, e. Antioxidants from our diet play an important role in helping endogenous antioxidants for the neutralization of oxidative stress.
The nutrient antioxidant deficiency is one of the causes of numerous chronic and degenerative pathologies. Each nutrient is unique in terms of its structure and antioxidant function 6 , Vitamin E.
Vitamin E is a fat-soluble vitamin with high antioxidant potency. Its antioxidant function mainly resides in the protection against lipid peroxidation. Vitamin E has been proposed for the prevention against colon, prostate and breast cancers, some cardiovascular diseases, ischemia, cataract, arthritis and certain neurological disorders.
In contrast, there is no increased risk of death with a dose of IU per day or less, and there may even be some benefit Although controversial, the use of long-term vitamin E supplementation in high dose should be approached cautiously until further evidence for its safety is available. The dietary sources of vitamin E are vegetable oils, wheat germ oil, whole grains, nuts, cereals, fruits, eggs, poultry, meat 6 , Vitamin C.
Vitamin C also known as ascorbic acid, is a water-soluble vitamin. It is essential for collagen, carnitine and neurotransmitters biosynthesis Health benefits of vitamin C are antioxidant, anti-atherogenic, anti-carcinogenic, immunomodulator. The positive effect of vitamin C resides in reducing the incidence of stomach cancer, and in preventing lung and colorectal cancer.
Vitamin C works synergistically with vitamin E to quench free radicals and also regenerates the reduced form of vitamin E. Natural sources of vitamin C are acid fruits, green vegetables, tomatoes. Ascorbic acid is a labile molecule, therefore it may be lost from during cooking Beta-carotene, Beta-carotene is a fat soluble member of the carotenoids which are considered provitamins because they can be converted to active vitamin A.
Beta-carotene is converted to retinol, which is essential for vision. It is a strong antioxidant and is the best quencher of singlet oxygen.
However, beta-carotene supplement in doses of 20mg daily for years has been associated with an increased risk of lung and prostate cancer and increased total mortality in cigarette smokers These adverse effects do not appear to occur in people who eat foods high in beta-carotene content. Beta-carotene is present in many fruits, grains, oil and vegetables carrots, green plants, squash, spinach 6. Lycopene, a carotenoid, possesses antioxidant and antiproliferative properties in animal and in vitro studies on breast, prostate and lung cell lines, although anticancer activity in humans remains controversial 6 , 45 , Lycopene has been found to be very protective, particularly for prostate cancer Several prospective cohort studies have found associations between high intake of lycopene and reduced incidence of prostate cancer, though not all studies have produced consistent results The major dietary source of lycopene is tomatoes, with the lycopene in cooked tomatoes, tomato juice and tomato sauce included, being more bioavailable than that in raw tomatoes Selenium Se.
Se is a trace mineral found in soil, water, vegetables garlic, onion, grains, nuts, soybean , sea food, meat, liver, yeast 6. It forms the active site of several antioxidant enzymes including glutathione peroxidase. At low dose, health benefits of Se are antioxidant, anti-carcinogenic and immunomodulator Selenium is also necessary for the thyroid function Selenium deficiency can occur in patients on total parenteral nutrition TPN and in patients with gastrointestinal disorders.
In certain China areas with Se poor soil, people have developed a fatal cardiomyopathy called Keshan disease which was cured with Se supplement The role of Se in cancer prevention has been the subject of recent study and debate. Results from clinical and cohort studies about cancer prevention, especially lung, colorectal, and prostate cancers are mixed 10 , Flavonoids are polyphenolic compounds which are present in most plants. According to chemical structure, over flavonoids have been identified and classified into flavanols, flavanones, flavones, isoflavones, catechins, anthocyanins, proanthocyanidins.
Beneficial effects of flavonoids on human health mainly reside in their potent antioxidant activity Every plant contains a unique combination of flavonoids, which is why different herbs, all rich in these substances, have very different effects on the body The main natural sources of flavonoids include green tea, grapes red wine , apple, cocoa chocolate , ginkgo biloba, soybean, curcuma, berries, onion, broccoli, etc. For example, green tea is a rich source of flavonoids, especially flavonols catechins and quercetin.
Catechin levels are times greater in green tea than in black tea. Many health benefits of green tea reside in its antioxidant, anticarcinogenic, antihypercholesterolemic, antibacterial dental caries , anti-inflammatory activities Omega-3 and omega-6 fatty acids.
They are essential long-chain polyunsaturated fatty acids because the human body cannot synthesize them. Therefore, they are only derived from food.
Omega-3 fatty acids can be found in fat fish salmon, tuna, halibut, sardines, pollock , krill, algae, walnut, nut oils and flaxseed. However, certain big fishes like tilefish, shark, swordfish are to be avoided because of their high mercury levels Dietary sources of omega-6 fatty acids linoleic acid include vegetable oils, nuts, cereals, eggs, poultry. It is important to maintain an appropriate balance of omega-3s and omega-6s in the diet, as these two substances work together to promote health 52 , Omega-3 fatty acids help reduce inflammation, and most omega-6 fatty acids tend to promote inflammation.
An inappropriate balance of these essential fatty acids contributes to the development of disease while a proper balance helps maintain and even improve health. A healthy diet should consist of about times more omega-6s than omega-3s.
This theory helps explain aging, since aging accelerates over time. The gradual, but increasingly rapid buildup of free radicals offers one explanation for why even healthy bodies age and deteriorate over time. Free radical theories of aging and disease may help explain why some people age more slowly than others.
Although free radicals are produced naturally in the body, lifestyle factors can accelerate their production. Those include:. These lifestyle factors have been linked to diseases such as cancer and cardiovascular disease.
So, oxidative stress might be a reason why exposure to these substances causes disease. It is hard to watch television without seeing at least one commercial that promises to fight aging with antioxidants. Antioxidants are molecules that prevent the oxidation of other molecules.
Antioxidants are chemicals that lessen or prevent the effects of free radicals. They donate an electron to free radicals, thereby reducing their reactivity. What makes antioxidants unique is that they can donate an electron without becoming reactive free radicals themselves. No single antioxidant can combat the effects of every free radical. Just as free radicals have different effects in different areas of the body, every antioxidant behaves differently due to its chemical properties.
In certain contexts , however, some antioxidants may become pro-oxidants, which grab electrons from other molecules, creating chemical instability that can cause oxidative stress. Thousands of chemicals can act as antioxidants. Vitamins C, and E, glutathione, beta-carotene , and plant estrogens called phytoestrogens are among the many antioxidants that may cancel out the effects of free radicals. Many foods are rich in antioxidants. Berries, citrus fruits, and many other fruits are rich in vitamin C, while carrots are known for their high beta-carotene content.
The soy found in soybeans and some meat substitutes is high in phytoestrogens. The ready availability of antioxidants in food has inspired some health experts to advise antioxidant-rich diets. The antioxidant theory of aging also led many companies to push sales of antioxidant supplements. Research on antioxidants is mixed. Most research shows few or no benefits. A study that looked at antioxidant supplementation for the prevention of prostate cancer found no benefits.
A study found that antioxidants did not lower the risk of lung cancer. In fact, for people already at a heightened risk of cancer, such as smokers, antioxidants slightly elevated the risk of cancer.
Some research has even found that supplementation with antioxidants is harmful, particularly if people take more than the recommended daily allowance RDA.
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