Antioxidants are a heterogeneous set of substances made up of vitamins, minerals, natural pigments and other plant compounds, and enzymes that block the damaging effect of free radicals. The term antioxidant means that it prevents the oxidation of other chemicals, which occur in metabolic reactions or by exogenous factors such as ionizing radiation.
What are antioxidants
As the name says, antioxidants are substances capable of acting against the normal damage caused by the effects of the physiological process of oxidation on animal tissue. Nutrients (vitamins and minerals) and enzymes (proteins in your body that help chemical reactions) are antioxidants. It is believed that antioxidants help in preventing the development of chronic diseases such as cancer , heart disease , stroke , Alzheimer's disease , rheumatoid arthritis and cataracts .
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Oxidative stress occurs when the production of harmful molecules, called free radicals, is beyond the protective capacity of antioxidant defenses. Free radicals are chemically active atoms or molecules that have an odd number of electrons in their outer orbit.
Examples of free radicals are superoxide anion, hydroxyl radical, transition metals such as iron and copper, nitric acid and ozone. Free radicals contain oxygen known as reactive oxygen species (ROS), which are the most biologically important free radicals. ROS includes superoxide radicals and hydroxyl radical plus oxygen derivatives that do not contain odd electrons, such as hydrogen peroxide and singlet oxygen.
Because they have one or more odd electrons, free radicals are highly unstable. They scour your body to appropriate or donate electrons and, for this reason, damage cells , proteins and DNA (genetic material). The same oxidative process also causes rancidness in the oil, brown color on peeled apples and rust on the iron.
It is impossible to avoid the damage caused by free radicals. They are the result of various organic processes and are precipitated by various exogenous (external) and endogenous (internal sources) factors of our body.
The oxidants that develop from the internal processes of our body are formed by the natural result of aerobic respiration , metabolism and inflammation. Exogenous free radicals are formed through environmental factors such as ozone pollution , sunlight, exercise , x-rays , nicotine, and alcohol . Our antioxidant system is not perfect, so with age, the cells are damaged by the buildup of oxidation.
The antioxidant process
Antioxidants block the oxidation process by neutralizing free radicals. By doing this, they themselves become oxidized. This is the reason why there is a constant need to recharge our antioxidant resources.
How Antioxidants Work
- - Chain break - When a free radical releases or steals an electron, a second electron is formed. This molecule circulates through the body and does the same thing with a third molecule, thus generating more unstable products. How does this happen? Or the radical is stabilized by an antioxidant that breaks the chain such as beta-carotene and vitamins C and E or simply breaks down into a harmless product.
- - Preventive - antioxidant enzymes such as superoxide dismutase, catalase and glutathione peroxidase prevent oxidation by reducing the rate of initiation of the chain. This means that by looking for radicals in the starter stage, such antioxidants can prevent the oxidation process from starting. These enzymes can also prevent oxidation by stabilizing transition metals such as copper and iron.
The effectiveness of any antioxidant in the body depends on the free radical that is involved, how and where it is generated and where the injury lies. Consequently, while in an particular body an antioxidant protects against free radicals, in another it may not have this same effect. In some circumstances they may even act as a pro-oxidant, which generates toxic species of oxygen.
Types of antioxidants
Antioxidant nutrients
The antioxidants in our diet seem to be of great importance in controlling the damage caused by free radicals. Each nutrient is unique in terms of structure and antioxidant function.
- Vitamin E is a generic name for all elements (to date, eight have been identified) that exhibit biological activity of the alpha tocopherol isomer. An isomer has two or more molecules with the same chemical formula and different atomic arrangements.
- Alpha tocopherol, the best known and available isomer on the market, has greater biopotency (greater effect on the body). Because it is soluble in fats , alpha tocopherol is in a unique position to protect the membranes of cells, which are mostly composed of fatty acids, from the damage caused by free radicals. It also protects fats in low-density lipoproteins (LDLs or "bad" cholesterol) from oxidation.
- Vitamin C , also known as ascorbic acid, is water soluble. Therefore, it looks for free radicals that are in an aqueous (liquid) environment, like what is inside our cells. Vitamin C works synergistically with vitamin E to eliminate free radicals. Vitamin C also regenerates the reduced (stable) form of vitamin E.
- Beta carotene is also a water-soluble vitamin and is widely studied among the 600 carotenoids identified so far. It is regarded as the best eliminator of singlet oxygen, which is an energized but oxygen-free form that is toxic to cells. Beta-carotene is excellent for looking for free radicals in a low oxygen concentration.
- Selenium is an essential element. It is a mineral that we need to consume in small quantities and without which we could not survive. It forms the active center of several antioxidant enzymes including glutathione peroxidase.
- Similar to selenium, the minerals manganese and zinc are microelements that form an essential part of the various antioxidant enzymes.
Antioxidant enzymes
The antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) serve as the primary defense line in the destruction of free radicals.
SOD first reduces (adds an electron) the superoxide radical (O 2 - ) to form hydrogen peroxide (H 2 O 2 ) and oxygen (O 2 ).
2O 2 - + 2H --SOD -> H 2 O 2 + O 2
Catalysis and GPx then work simultaneously with the protein glutathione to reduce hydrogen peroxide and ultimately produce water (H 2 O).
2H 2 O 2 -CAT -> H 2 O + O 2
H 2 O 2 + 2glutathione --GPx -> oxidized glutathione + 2H 2 O
2H 2 O 2 -CAT -> H 2 O + O 2
The oxidized glutathione is then reduced by another oxidizing enzyme - glutathione reductase.
Together, they repair oxidized DNA, reduce oxidized protein, and destroy oxidized lipids, fat-like substances that are components of cell membranes. Several other enzymes act as a secondary antioxidant defense mechanism to protect you from future damage.
Other antioxidants
In addition to enzymes, vitamins and minerals, there are other nutrients and compounds that have antioxidant properties. Among them is coenzyme Q10 (CoQ10 or ubiquinone), which is essential for the production of energy and protection of the body against destructive free radicals. Uric acid, a product of DNA metabolism, is recognized as an important antioxidant. In addition, substances in plants called phytochemicals are being studied for their antioxidant activities and the potential for health promotion.
Antioxidants improve health
Since antioxidants act against the damaging effects of free radicals, we could think of consuming as much of them as possible. However, even being components necessary for good health, it is still unclear whether supplements should be taken.
And if so, what is the amount to be consumed. Supplements have long been thought to be harmless, but it is now known that the consumption of high doses of antioxidants can be harmful because of the high potential for toxicity and drug interaction. Remember: antioxidants alone can act as pro-oxidants at high levels.
So, is there any scientific basis for all this hype about antioxidants? The experimental studies performed so far have different results, listed below.
- - The Cancer Prevention Study with Beta-Carotene and Alpha Tocopherol (ATBC) involved Finnish smokers and alcohol users. The volunteers received doses of 20 mg of synthetic beta-carotene or 50 mg of vitamin E or a combination of the two or a placebo.
After eight years, volunteers who took vitamin E had 32 percent fewer diagnoses of prostate cancer and 41 percent fewer deaths from prostate cancer compared to men who did not take vitamin E. However, after only four years, there were 16 percent more cases of lung cancer and 14% more deaths from lung cancer in the group that took only beta-carotene.
- - In the Retinol and Carotenoid efficacy experiment (CARET), volunteers were smokers or workers exposed to asbestos. They received a combination of 30 mg of synthetic beta-carotene and 25,000 IU (international units) of retinol (preformed vitamin A) or placebo. This study was stopped early because preliminary results showed a 28% increase in lung cancer rate in the group taking beta-carotene compared to the placebo group.
- - A health study (PHS) of 22,000 physicians, of whom 11% were smokers and 40% ex-smokers, showed no protective effect or toxic effect after 12 years of follow-up. Participants were randomly assigned to receive either 50 mg of beta-carotene on interspersed days or placebo. A second PHS study is underway to test beta-carotene, vitamin E, vitamin C and multivitamin with folic acid in healthy men aged 65 years or older to decrease cognitive decline.
- - A 1997 study published in the Journal of the American Medical Association found that 60 mg of vitamin E per day boosted the immune system in a group of 65-year-old healthy patients and 200 mg generated a greater improvement after four months. However, 800 mg of vitamin E resulted in a worse immunity than they would have if they had not received any doses.
- - In 2001, the National Institute of Health promoted a medical research on eye diseases in relation to age (AREDS). A randomized controlled trial showed that high-dose supplements such as 500 mg of vitamin C, 400 IU of vitamin E, 15 mg of beta-carotene, 80 mg of zinc and 2 mg of copper significantly reduced the risk of age-related macular degeneration (AMD) compared to placebo. In addition, the group that took antioxidant and zinc had a significant reduction in visual acuity loss rates.
There are several possible explanations for these results:
- - the amount of antioxidants in supplements may be as high as compared to that in the diet leading to a toxic effect;
- - other nutrients may be present in fruits and vegetables that function in sync with antioxidants and are needed to provide a protective effect;
- - study participants were too old to start taking antioxidants or had life-threatening lifestyles that antioxidants could not reverse the picture.
More than that, numerous observational studies, in which researchers look for associations without providing participants with supplements, have associated rich diets of fruit and vegetable antioxidants with a lower risk of diseases such as cancer, coronary disease, stroke, cataracts, malaria of Parkinson's, Alzheimer's and arthritis. So, despite the disappointing findings of the experiments, scientists are convinced of the many potential benefits of antioxidant diets rich in fruits and vegetables (but remember that antioxidants should be ingested in natura as part of the diet). They simply have not yet been able to calculate exactly how different antioxidant systems work together in our body to protect us from free radical damage.
How much is needed
The American Heart Association , for example, does not recommend the use of antioxidant supplements "until more information is compiled," but instead suggests that people "eat a variety of foods on a daily basis of all basic groups ".
More than that, in April 2000, the Food and Nutrition Board of the Institute of Medicine, a board that is part of the National Academy of Sciences, reported that vitamin C, vitamin E, selenium and carotenoids like beta-carotene should come from foods, not from supplements.
After examining available data on the beneficial and detrimental effects of antioxidants on health, the board concluded that there is no evidence to support the use of high doses of these nutrients to combat chronic diseases. In fact, the council warned that high doses of antioxidants can lead to health problems, including diarrhea, bleeding and the risk of toxic reactions.
Since 1941, the Food and Nutrition Board has determined the types and quantities of nutrients that are needed for a healthy diet by analyzing the scientific literature, considering how nutrients protect against disease and interpreting nutrient intake data.
For each type of nutrient, the Board establishes a Recommended Dietary Allowance (RDA) which is a daily intake goal for nearly all (98%) healthy individuals and a "maximum tolerable intake level" (UL) which is the maximum amount of a nutrient that a healthy individual can ingest every day without the risk of adverse health effects.
In some cases, the Board decides that there is insufficient evidence to determine how much of a particular nutrient is essential or harmful to health.
Over the past few years, the Board has updated and expanded the system to determine the RDA and UL values that are now collectively referred to as Dietary Reference Intakes or DRIs.
Where Antioxidants Are Found
While the research looks promising, particularly with regard to vitamin E, food is the smartest choice for antioxidants. Studies show that for good health you need to eat at least five servings of fruits and vegetables every day as part of a balanced diet. Below is a list of where to find the specific antioxidants. If you are interested in taking antioxidant supplements, talk to your doctor about what is best for you.
Vitamin E is found in vegetable oils, nuts, peanuts, almonds, seeds, olives, avocados, wheat germ, liver and green leaves.
- - For good sources of vitamin C , look for citrus fruits like orange, broccoli, green leaves, tomatoes, peppers, peppers, potatoes, cantaloupe and strawberries.
Common sources of beta carotene include melon, mango, papaya papaya, pumpkin, bell pepper, pepper, spinach, cabbage, zucchini, sweet potato and apricot.
- - You can find selenium in seafood, beef, pork, chicken, Brazil nut, brown rice and whole wheat bread .
Phytochemicals are found in a variety of sources. Some phytochemicals are currently under study to discover the antioxidant properties and abilities of reducing the risk of diseases that are listed below.
- Phytochemical and its source of food:
- Allylic sulphide (Onion, garlic, leeks, chives)
- Carotenoids (eg lycopene, lutein and zeaxanthin) (Tomato, carrot, watermelon, cabbage, spinach)
- Curcumin (Earth Safflower)
- Flavonoids (eg anthocyanin, resveratrol, quercetin and catechin) (Grape, blackcurrant, strawberry, cherry, apple, blackberry, raspberry and wildberry)
- Glutathione (green leaves)
- Indol (Broccoli, cauliflower, cabbage, Brussels sprouts and chicory)
- Isoflavonoids (eg genistein, daidzein) (Vegetables (peas and soybeans)
- Isothiocyanate (eg sulforafane) (Broccoli, cauliflower, Brussels sprouts and chicory)
- Lignins Seeds (flax seeds and sunflower seeds)
- Monoterpeno (peels of citrus fruits, cherry and nuts)
- Phytic acid (whole grains and vegetables)
- Phenol, polyphenol and phenolic compounds (eg ellagic acid, ferulic acid and tannin) (Grape, blueberry, strawberry, cherry, grapefruit, blackberry, raspberry, blackberry and tea)
- Saponino (Beans and legumes)
Of course, in addition to eating lots of fruits and vegetables, regular exercise and abstaining from smoking are essential for a healthy lifestyle.