Wednesday, February 7, 2018

Antioxidants – Types Of Antioxidants And Their Role In Body Protection


Antioxidants is the name of the groups which has the anti-oxidative by preventing free-radical, for example:

- Vitamin A
- Vitamin C (ascorbic acid)
- Vitamin E (mostly alpha-tocopherol)
- Carotenoids (mostly beta-carotene)
- Anthocyanins
- Catechins
- Lutein
- Lycopene
- Selenium
- Manganese
- Ellagic acid
- Resveratrol
- Zeaxanthin
- ...

Antioxidants are present in large amounts in several foods. However, the actual amount of antioxidants in several plant products may differ due to several factors. These include:

- soil type and chemistry
- available nitrogen and levels of other plant nutrients
- moisture levels
- temperature
- pests

It has been seen that plants which are exposed to stress are driven to synthesize antioxidants and are richer in these polyphenols and flavonoids.

Food rich in antioxidants are shown here:
To protect the cells and organ systems of the body against reactive oxygen species, humans have evolved a highly sophisticated and complex antioxidant protection system. It involves a variety of components, both endogenous and exogenous in origin, that function interactively and synergistically to neutralize free radicals. These components include:

• Nutrient-derived antioxidants like ascorbic acid (vitamin C), tocopherols and tocotrienols (vitamin E), carotenoids, and other low molecular weight compounds such as glutathione and lipoic acid.

• Antioxidant enzymes, e.g., superoxide dismutase, glutathione peroxidase, and glutathione reductase, which catalyze free radical quenching reactions.

• Metal binding proteins, such as ferritin, lactoferrin, albumin, and ceruloplasmin that sequester free iron and copper ions that are capable of catalyzing oxidative reactions.

• Numerous other antioxidant phytonutrients present in a wide variety of plant foods.

DIETARY ANTIOXIDANTS

Vitamin C, vitamin E, and beta-carotene are among the most widely studied dietary antioxidants. Vitamin C is considered the most important water-soluble antioxidant in extracellular fluids. It is capable of neutralizing ROS in the aqueous phase before lipid peroxidation is initiated. Vitamin E, a major lipid-soluble antioxidant, is the most effective chain-breaking antioxidant within the cell membrane where it protects membrane fatty acids from lipid peroxidation. Vitamin C has been cited as being capable of regenerating vitamin E [3].

Beta-carotene and other carotenoids are also believed to provide antioxidant protection to lipid-rich tissues. Research suggests beta-carotene may work synergistically with vitamin E. A diet that is excessively low in fat may negatively affect beta-carotene and vitamin E absorption, as well as other fat-soluble nutrients. Fruits and vegetables are major sources of vitamin C and carotenoids, while whole grains and high quality, properly extracted and protected vegetable oils are major sources of vitamin E.

PHYTONUTRIENTS

A number of other dietary antioxidant substances exist beyond the traditional vitamins discussed above. Many plant-derived substances, collectively termed “phytonutrients,” or “phytochemicals,” are becoming increasingly known for their antioxidant activity. Phenolic

compounds such as flavonoids are ubiquitous within the plant kingdom: approximately 3,000 flavonoid substances have been described. In plants, flavonoids serve as protectors against a wide variety of environmental stresses while, in humans, flavonoids appear to function as “biological response modifiers.” Flavonoids have been demonstrated to have anti-inflammatory, antiallergenic, anti-viral, anti-aging, and anti-carcinogenic activity.

The broad therapeutic effects of flavonoids can be largely attributed to their antioxidant properties. In addition to an antioxidant effect, flavonoid compounds may exert protection against heart disease through the inhibition of cyclooxygenase and lipoxygenase activities in platelets and macrophages.

The best way to ensure an adequate intake of phytonutrients is to eat a diet rich in a wide variety of fresh fruits and vegetables. Phytonutrient supplements are also now widely available

ENDOGENOUS ANTIOXIDANTS

In addition to dietary antioxidants, the body relies on several endogenous defense mechanisms to help protect against free radical-induced cell damage. The antioxidant enzymes – glutathione peroxidase, catalase, and superoxide dismutase (SOD) – metabolize oxidative toxic intermediates and require micronutrient cofactors such as selenium, iron, copper, zinc, and manganese for optimum catalytic activity. It has been suggested that an inadequate dietary intake of these trace minerals may compromise the effectiveness of these antioxidant defense mechanisms. Research indicates that consumption and absorption of these important trace minerals may decrease with aging. [4] Intensive agricultural methods have also resulted in significant depletion of these valuable trace minerals in our soils and the foods grown in them.

Glutathione, an important water-soluble antioxidant, is synthesized from the amino acids glycine, glutamate, and cysteine. Glutathione directly quenches ROS such as lipid peroxides, and also plays a major role in xenobiotic metabolism. Exposure of the liver to xenobiotic substances induces oxidative reactions through the upregulation of detoxification enzymes. When an individual is exposed to high levels of xenobiotics, more glutathione is utilized for conjugation (a key step in the body’s detoxification process) making it less available to serve as an antioxidant. Research suggests that glutathione and vitamin C work interactively to quench free radicals and that they have a sparing effect upon each other.[5]

Lipoic acid, yet another important endogenous antioxidant. Lipoic acid and its reduced form, dihydrolipoic acid (DHLA), are capable of quenching free radicals in both lipid and aqueous domains and as such has been called a “universal antioxidant.”[6] Lipoic acid may also exert its antioxidant effect by chelating with pro-oxidant metals. Research further suggests that lipoic acid has a sparing effect on other antioxidants.[6,7] Animal studies have demonstrated supplemental lipoic acid to protect against the symptoms of vitamin E or vitamin C deficiency.[6] Additional physiological antioxidants are listed here:

Endogenous Antioxidants
• Bilirubin
• Thiols, e.g., glutathione, lipoic acid, N-acetyl cysteine
• NADPH and NADH
• Ubiquinone (coenzyme Q10)
• Uric acid
• Enzymes:
– copper/zinc and manganese-dependent superoxide
dismutase (SOD)
– iron-dependent catalase
– selenium-dependent glutathione peroxidase
Dietary Antioxidants
• Vitamin C
• Vitamin E
• Beta-carotene and other carotenoids and oxy carotenoids, e.g., lycopene and lutein
• Polyphenols, e.g., flavonoids, flavones, flavonols, and proanthocyanidins
Metal Binding Proteins
• Albumin (copper)
• Ceruloplasmin (copper)
• Metallothionein (copper)
• Ferritin (iron)
• Myoglobin (iron)
• Transferrin (iron)

Each of antioxidants nutrients has the different role in preventing free-radicals. Foods probably contain other antioxidants that are still undiscovered. Eating a wide variety of foods will help you get the full benefit of these antioxidants.

References

[1] Antioxidants, Dr.Mark Percivals, Clinical Nutrition Insights, 1996
[2] Antioxidants Handouts, American Dietetic Association, 2010
[3] Halliwell, B., Free Radicals, Antioxidants, and Human Disease: Curiosity, Cause, or Consequence?
Lancet 1994;344:721-724.
[4] Duthie, G.G., and Brown, K.M., Reducing the Risk of Cardiovascular Disease, ch 2, p. 19-38, In: Functional Foods, ed. Goldberg, I. Chapman and Hall: New York 1994.
[5] Jacob, R.A., The Integrated Antioxidant System. Nutr Res 1995;15(5):755-766.
[6] Packer, L. and Witt, E.H., Antioxidant Properties and Clinical Implications of Alpha-Lipoic Acid. in Packer L. and Cadenas E. eds. Biothionls in Health and Disease. New York: Marcel Dekker, Inc, 1995, 479-516.
[7] Kagen, V.E., et al., Dihydrolipoic Acid–a Universal Antioxidant Both in the Membrane and in the Aqueous Phase. Biochem Pharmacol 199244:1637-1649.

at No comments:
Labels:

Monday, February 5, 2018

Food Substances - The Fact Of Antioxidants


All living organisms utilize oxygen to metabolize and use the dietary nutrients in order to produce energy for survival. Oxygen thus is a vital component for a living. Oxygen meditates chemical reactions that metabolize fats, proteins, and carbohydrates to produce energy.

1. OXYGEN AND FREE-RADICALS

a) Dark side of oxygen

While oxygen is one of the most essential components for the living, it is also a double-edged sword. Oxygen is a highly reactive atom that is capable of becoming part of potentially damaging molecules commonly called “free radicals.”

b) Free radicals

These free radicals are capable of attacking the healthy cells of the body. This may lead to damage, disease and severe disorders. Cell damage caused by free radicals appears to be a major contributor to aging and diseases like:
- cancer
- heart disease
- the decline in brain function
- the decline in immune system etc.

Overall, free radicals have been implicated in the pathogenesis of at least 50 diseases.

Since free radicals contain an unpaired electron they are unstable and reach out and capture electrons from other substances in order to neutralize themselves. This initially stabilizes the free radical but generates another in the process. Soon a chain reaction begins and thousands of free radical reactions can occur within a few seconds on the primary reaction.

c) Reactive oxygen species (ROS)

ROS is a term which encompasses all highly reactive, oxygen-containing molecules, including free radicals. Types of ROS include the hydroxyl radical, hydrogen peroxide, the superoxide anion radical, nitric oxide radical, singlet oxygen, hypochlorite radical, and various lipid peroxides. These can react with membrane lipids, nucleic acids, proteins and enzymes, and other small molecules.

d) Oxidative stress

Oxidative stress means an unbalance between pro-oxidants and antioxidant mechanisms. This results in excessive oxidative metabolism. This stress can be due to several environmental factors such as exposure to pollutants, alcohol, medications, infections, poor diet, toxins, radiation etc. Oxidative damage to DNA, proteins, and other macromolecules may lead to a wide range of human diseases most notably heart disease and cancer.

2. ANTIOXIDANTS

a) How to control of free radicals

Normally free radical formation is controlled naturally by various beneficial compounds known as antioxidants. When there is a deficiency of these antioxidants damage due to free radicals can become cumulative and debilitating.

Antioxidants are capable of stabilizing, or deactivating, free radicals before they attack cells.

b) How do antioxidants work?

In order to understand how antioxidants work, we must start at the molecular level...

As you may know, all matter in the universe is made of atoms.

Atoms are composed of a core with protons and neutrons, and a bunch of electrons that revolve around the core.

Here is a simple diagram of an atom:


The blue balls are electrons, which carry a negative (-) charge, while the protons (red balls) in the core carry a positive (+) charge. 

When two or more atoms are linked together, they become what we know as molecules. 

The human body is made up of substances like proteins, fats and DNA, which are basically just large molecules with dozens, hundreds or thousands of atoms joined together. 

This is an image of a fatty acid molecule. Each ball represents an atom:


In these chemical reactions, bigger molecules are broken down into smaller molecules, and smaller molecules are organized into bigger molecules. 

In order for a molecule to be stable, it must contain the right amount of electrons. If the molecule loses an electron when it isn't supposed to, it can turn into a free radical. 

Free radicals are unstable, electrically charged molecules in the cells, that can react with other molecules (like DNA) and damage them. 

They can even form chain reactions, where the molecules they damage also turn into free radicals. 

This is where antioxidants come in... if a molecule loses an electron and turns into a free radical, the antioxidant molecule steps in and "gives" the free radical an electron, effectively neutralizing it. 

This is how it happens:
This is the mechanism behind antioxidants. They donate electrons to free radicals, which neutralizes them and prevents them from causing harm.

c) Antioxidants and free radicals are both important

Free radicals are constantly being formed during metabolism. 

Without antioxidants, they would destroy our bodies very quickly. 

However, it's important to keep in mind that free radicals also serve important functions that are essential for our survival [2]. 

For example, the body's immune cells use free radicals to kill bacteria that try to infect us [3]. 

As with so many things in the body, we need a certain balance... we need the right amount of free radicals, and the right amount of antioxidants to keep them in check. 

When this balance gets disrupted, things can start to go wrong. 

When the free radicals (pro-oxidants) outnumber the antioxidants, this can lead to oxidative stress.

3. SOURCE OF ANTIOXIDANTS 

a) Antioxidants from food 

There are several nutrients in food that contain antioxidants. Vitamin C, vitamin E, and beta-carotene are among the most commonly studied dietary antioxidants. 

Vitamin C is the most important water-soluble antioxidant in extracellular fluids. Vitamin C helps to neutralize ROS in the water or aqueous phase before it can attack the lipids. 

Vitamin E is the most important lipid-soluble antioxidant. It is important as the chain-breaking antioxidant within the cell membrane. It can protect the membrane fatty acids from lipid peroxidation. Vitamin C, in addition, is capable of regenerating vitamin E. 

Beta-carotene and other carotenoids also have antioxidant properties. Carotenoids work in synergy with vitamin E. 

b) Antioxidant deficiencies 

A diet low in fats may impair absorption of beta-carotene and vitamin E and other fat-soluble nutrients. Fruits and vegetables are important sources of vitamin C and carotenoids. Whole grains and high-quality vegetable oils are major sources of vitamin E. 

Many plant-derived substances are known as “phytonutrients,” or “phytochemicals”. These also possess antioxidant properties. Phenolic compounds such as flavonoids are such chemicals. These are found in several fruits, vegetables, green tea extracts etc. 

c) Antioxidants within the human body 

Apart from diet, the body also has several antioxidant mechanisms that can protect itself from ROS mediated damage. The antioxidant enzymes – glutathione peroxidase, catalase, and superoxide dismutase (SOD) are such enzymes. They require micronutrient cofactors such as selenium, iron, copper, zinc, and manganese for their activity. It has been suggested that an inadequate dietary intake of these trace minerals may also lead to low antioxidant activity. 

4. SHOULD WE TAKE ANTIOXIDANT SUPPLEMENTS? 

Dietary intake of antioxidants is essential for optimal health. 

However, more is not always better. 

Excessive intake of isolated antioxidants can have toxic effects and may even promote rather than prevent oxidative damage. 

In fact, some studies have shown that high doses of antioxidants increase the risk of death [4, 5]. 

Therefore, you should avoid high-dose antioxidant supplementation. 

In addition, studies show that foods reduce oxidative damage more than supplements. 

For example, a study using blood orange juice showed that it had significantly greater antioxidant power than a drink with sugar water that contained the same amount of Vitamin C [6]. 

The truth is... real foods have hundreds (if not thousands) of different nutrients that work synergistically. Taking just one or two isolated nutrients won't have the same beneficial effects. 

The best (and healthiest) strategy to ensure adequate intake of antioxidants, is a diet rich in various vegetables and fruit [7], along with other healthy dietary habits. 

However, low-dose supplementation, such as in multivitamin tablets, may be beneficial if you are deficient in certain nutrients or unable to follow a healthy diet. 

References 




Tag: avyannakate, how to prevent cancer, how to treat cancer, food substances, what is antioxidant, what are antioxidants, the fact of antioxidants, what do antioxidants work; diabetes
at 1 comment:
Labels:
Subscribe to: Posts (Atom)