Antioxidant

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An antioxidant is a chemical that slows or halts oxidation (most in context of organic substances). It is in effect a reducing agent in free-radical reactions.

Contents

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Mechanism

An antioxidant may act by catalysis, or, in cells, it may act as a cofactor that transfers reducing equivalents from NADPH. Antioxidants first gained prominence as retardants of the vulcanization of rubber, and later in nutrition with the identification of vitamins A, C, and E and various non-nutrient phytochemicals as antioxidants. Antioxidants are popular ingredients in dietary supplements, and are used in the hope of reducing risks of cancer and extending life. However, while some clinical trials support this belief, others do not.

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Antioxidants in biology

In biological systems, the normal processes of oxidation (plus contributions from ionizing radiation and pro-oxidant chemicals) produce highly reactive free radicals. These can readily react with and damage other molecules, including DNA in cell nuclei or mitochondria. In some cases, the body uses free radicals to destroy foreign or unwanted objects, such as in an infection or cancer. However, in the wrong place, the body's own cells may become damaged. Should the damage occur to DNA, the result could increase the possibility of cancer. Antioxidants decrease the damage done to cells by reducing oxidants before they can damage the cell. Antioxidants may be further classified by the products they form on oxidation (these can be antioxidants themselves, inert, or pro-oxidant), by what happens to the oxidation products (the antioxidant may be regenerated by different antioxidants or, in the case of "sacrificial" antioxidants, its oxidised form may be broken down by the organism) and how effective the antioxidant is against specific free radicals.

Free radical damage in the mitochondria of living cells is a byproduct of oxidative phosphorylation. Superoxide radicals are generated, which can damage mitochodrial 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 they are too hydrophilic to cross mitochondrial membranes or too hydrophobic to cross the cytoplasm). Melatonin is an important natural antioxidant that has been demonstrated to strongly protect mitochondria from damage [1], [2]. 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.

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Applications in Nutrition and in Medicine

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How antioxidants preserve health

Free radicals are atoms or molecules with unpaired electrons, making them highly reactive and oxidative. Some of the common free radicals inside the human body are the hydroxyl, peroxide, and superoxide radicals, and metal ions. Free radicals serve important functions inside the body, but they can also damage cells and biochemicals.

Antioxidants are chemicals that bind with and destroy free radicals, reducing oxidative damage to cells and biochemicals. Researchers have found high correlation between oxidative damage to cells and biochemicals, and the occurence of disease. For example, LDL oxidation is associated with cardiovascular disease. The process leading to atherogenesis, artherosclerosis, and cardiovascular disease is complex, involving multiple chemical pathways and networks, but the precursor is LDL oxidation by free radicals, resulting in inflammation and formation of plaques.

Research suggests that consumption of antioxidant-rich foods reduces damage to cells and biochemicals from free radicals. This can slow down, prevent, and even reverse certain diseases that result from cellular damage, and perhaps even slow down the natural aging process (see free-radical theory of aging).

Some of the reactions in the body that produce free radicals involve metal ions. Futhermore, metal ions are themselves free radicals that can cause oxidation directly. Some antioxidants, such as the tannins in walnuts, chelate (wrap around) metal ions. This not only reduces the formation of ion-dependent free radicals, but also prevents the metal ions from oxidizing cells and biochemicals directly.

By destroying free radicals and reducing cellular damage, antioxidants, as a group, can:

  • Promote eye health and prevent macular generation, cataracts, and other degenerative eye diseases. The benefits of antioxidants were examined during the Age-Related Eye Disease Study.
  • Keep the immune system in good shape, or boost the immune system when it has been compromised.
  • Prevent age-related neurodegeneration (decline of the brain and nervous system).
  • Prevent DNA damage and therefore have anticarcinogenic effects (that is, help prevent cancer).
  • Have antiatherogenic effects (that is, promote cardiovascular health and help prevent artherosclerosis, heart attacks, strokes, and other cardiovascular diseases). Antioxidants can decrease LDL and cholesterol, increase HDL, and lower blood pressure. The mechanisms behind these effects are not fully understood, and can occur even if the person has a diet high in saturated fat.

Any specific antioxidant may perform only a small fraction of these functions.

Dietary antioxidants are not the primary antioxidant inside the body, and there are still many questions as to how polyphenols and other dietary antioxidants protect cells and biochemicals from oxidation. Some antioxidants preserve, or even recycle, other antioxidants such as vitamin E. Some antioxidants have far-reaching effects, such as moderating insulin, that are not clearly understood.

Antioxidants are not the only substances that are heart-healthy. Unsaturated fatty acids, especially those that are of the omega-3 and polyunsaturated type, and amino acids such as arginine, also help preserve cardiovascular health. Consumption of omega-3 fatty acids can decrease blood pressure, LDL, and inflammation, stabilize heart rhythms, and reduce the risk of autoimmune disorders such as arthritis. Fish such as wild salmon are rich in omega-3 fatty acids. Omega-3 fatty acids prevent the formation of atherosclerosis when they are taken in conjunction with antioxidants. The antioxidants prevent the acids from being oxidised.

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How some antioxidants can harm health

Some of the plant based reducing acids, most notably oxalic and phytic, bind to needed dietary minerals, rendering them unabsorbable in the gastrointestinal tract. Some of the tannins also have this negative characteristic. Calcium and iron deficiencies are not uncommon in mideastern diets where there is high consumption of phytic acid present in beans and unleavened whole grain bread. Such antinutrients can sometimes result in deceptively high Oxygen Radical Absorbance Capacity (ORAC) ratings given to various "healthy" beverages and foods, particularly:

Other extremely powerful nonpolar antioxidants such as eugenol also happen to have toxicity limits that can easily be exceeded with the misuse of essential oils.

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Quick fatty acid lesson

  • Fatty acids are either saturated (no double-bonded carbon) or unsaturated (contain at least one double-bonded carbon).
  • Monounsaturated fatty acids have one double bond. Polyunsaturated fatty acids have more than one.
  • Unsaturated fatty acids are either omega-3, omega-6, or omega-9, depending on the position of the first double bond.
  • Humans can synthesize omega-9, but not omega-3 or omega-6, fatty acids, so certain precursor omega-3 and omega-6 fatty acids are deemed "essential". See essential fatty acid.
  • Triglycerides are three fatty acids bound to a glycerin molecule.
  • Lipoproteins are fatty acid and protein molecules that transport cholesterol between the intestines, liver, and cells in the rest of the body.
  • Antioxidants play a role in protecting fatty acids during cholesterol transport, as well as during creation of immune system and hormonal molecules such as prostaglandin.
  • For more details, see fatty acid, cholesterol, and related articles.
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Calorie restriction and reduced oxidative stress

Virtually all studies of mammals have concluded that a restricted calorie diet (CR) extends median and maximum lifespan (CR is almost the only protocol to have achieved this). This benefit appears to be at least partly due to substantially reduced oxidative stress [3]. Very large increases in lifespan (up to around 100%) have only been observed in short lived species and the effect in humans is expected to be far less dramatic. The best evidence from animal studies is likely to come from ongoing studies in primates where median life spans have already been shown to be increased and biomarkers of health significantly improved. Due to the long life span of primates, confirmation of maximum lifespan increase will not be available until around 2014 [4]. The striking results from animal experiments provide strong evidence that an excess of food reduces life expectancy, although the relationship is not a simple one. Other research suggests that being a little overweight is actually a healthier option in humans (New Scientist 26 November 2005), and a recent major study concluded that mortality rates were positively correlated with waist size, but for a fixed waist size mortality rates were negatively correlated with body mass index (particularly for underweight subjects) [5]. As food produces free radicals (oxidants) when metabolized, antioxidant-rich diets are thought to stave off the effects of aging significantly better than diets lacking in antioxidants.

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Dietary requirements

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. One study of lung cancer patients found that those given beta-carotene supplements had worse prognoses. Two 1994 studies found an increased rate of lung cancer in smokers supplementing with beta carotene. 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. In vitro testing (outside the body) has shown many natural antioxidants, in specific concentration, can halt the growth of or even kill cancerous cells.

There have been several clinical studies showing moderately increased levels of intake of specific antioxidants help to reduce the incidence of certain cancers. The recent SU.VI.MAX study in France concluded that low-dose supplementation (with 120 mg of ascorbic acid, 30 mg of vitamin E, 6 mg of beta carotene, 100 <math>\mu</math>g of selenium, and 20 mg of zinc) resulted in a 31% reduction in the incidence of cancer and a 37% reduction in all cause mortality in males, but did not get a significant result for females [6]. High levels of antioxidants can be powerful agents against tumours, but in some scenarios can interfere with the effects of other cancer treatments.

Recent laboratory studies suggest that at levels much higher than occur through normal diets, antioxidant vitamins such as A, E and C can have pro-oxidant effects, increasing the formation of free radicals. Natural antioxidants are always ingested together with a wide variety of flavonoids and other phytochemicals are also likely to play a part. Many supplement manufacturers supply products containing antioxidants in combination with these other natural chemicals. Another significant factor is that the mechanisms by which different antioxidants regenerate each other require balanced levels to work optimally. Newer liquid nutritional supplements using plant ionic compounds are believed to be more readily absorbed in the human body.

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Antioxidants in food industry - Food preservatives

Antioxidants used as food additives to help guard against food deterioration include:

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Food Supplements

Many nutraceutical and health food companies have, in light of scientific studies, produced products that supplement the diet with antioxidants. Many companies have products that are explicitly composed of derivatives that contain antioxidants, like resveratrol in grape seeds. Other companies produce supplements that contain a combination of antioxidants, like elagic acid with tummeric, or the ubiquitous "ACES" formulas that contain beta carotene (provitamin A), vitamin C, vitamin E and Selenium often with additional antioxidants and nutrients. Specialty herbs such as green tea and jiaogulan have benefitted tremendously from recent articles on antioxidants in green tea delaying onset of age-related macular degeneration.

Antioxidants especially recognized for their liver protective properties as well as other uses in conventional, naturopathic and orthomolecular medicine include:

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Nutritional antioxidants

There are hundreds of different types of antioxidants. The following substances have shown positive nutritional antioxidant effects:

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Vitamins

  • 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 (which gain their color from the compound lycopene), kale, seabuckthorn, 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, blueberries, seabuckthorn, 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, seabuckthorn, nuts, seeds, whole grains, green leafy vegetables, vegetable oil, and fish-liver oil. Recent studies showed that some tocotrienol isomers have significant anti-oxidant properties.
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Vitamin cofactors and minerals

  • Coenzyme Q10 (CoQ10) is an antioxidant which is both water and lipid soluble. It is not classified as a vitamin in humans as it can be manufactured by the body, but quantities decrease with age to levels that may be less than optimal, and levels in the diet are generally low. Supplementation with CoQ10 has been clinically proven to improve the health of gums. There is evidence that CoQ10 helps protect the brain against Parkinson's disease.
  • Selenium has been shown as early as the 1950's to have a beneficial effect in reducing the occurrence of male prostate cancer, and a recent study done by the National Health System of China have verified previous results. However, the substance 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, turkey, garlic, and Brazil nuts. Vegetables can also be a good source if they are grown in selenium-rich soils, and some nutritional supplements contain a supply of selenium.
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Hormones

  • Melatonin is a natural hormone which has several biological roles in different species. It is an exceptionally effective antioxidant within the mitochondria, which are subject to extreme oxidative stress.
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Carotenoid terpenoids

  • Lycopene - found in high concentration in ripe red tomatoes.
  • Lutein - found in high concentration in spinach and red peppers.
  • Alpha-carotene
  • Beta-carotene - found in high concentrations in butternut squash, carrots, orange bell peppers, pumpkins, and sweet potatoes.
  • Zeaxanthin - the main pigment found in yellow corn.
  • Astaxanthin - found naturally in red algae and animals higher in the marine food chain. It is a red pigment familiarly recognized in crustacean shells and salmon flesh/roe.
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Non-carotenoid terpenoids

Eugenol - has by far the highest Oxygen Radical Absorbance Capacity (ORAC) of all foodborn substances (in clove oil)[7]. Its concentration in clove oil ranges 5-20 times greater than where it is found in other sources[8] such as in basil and cinnamon.

Saponins and limonoids Editor's note: Not certain if these are antioxidants; work in progress...

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Flavonoid polyphenolics (also known as bioflavonoids)

Bioflavonoids are present in many dark berries such as pomegranate,seabuckthorn, noni, blueberries, and blackberries, as well as in certain types of tea and coffee, especially green tea. Coffee is often depleted of antioxidants due to the high-temperature roasting process. Applied Food Sciences has introduced Healthy Roast, a product that removes antioxidants from the green coffee beans before roasting and then adds them back when beans are quenched. The FDA may have recently suggested that the average person should consume up to 7000 ORAC units daily, in order to reduce the risk of cancer. As this is nearly 12 servings of high-ORAC-value fruit, the use of nutritional supplements containing bioflavonoids is likely necessary to reach this target.

Flavonols:

  • Resveratrol - found in the skins of dark-colored grapes, and concentrated in red wine.
  • Kaempferol
  • Myricetin
  • Isorhamnetin
  • Proanthocyanidins, or condensed tannins

Flavones:

Flavanones:

  • Hesperetin (metabolizes to hesperidin)
  • Naringenin (metabolized from naringin)
  • Eriodictyol

Flavan-3-ols:

  • Catechin
  • Gallocatechin
  • Epicatechin and its gallate forms
  • Epigallocatechin and its gallate forms
  • Theaflavin and its gallate forms
  • Thearubigins

Isoflavone phytoestrogens - found primarily in soy, peanuts, and other members of the Fabaceae family. Besides having antioxidant characteristics, isoflavones also protect and maintain the skeletal system.

  • Genistein
  • Daidzein
  • Glycitein

Anthocyanins (also known as anthocyanidins?) protect plants from UV damage:

  • Cyanidin
  • Delphinidin
  • Malvidin
  • Pelargonidin
  • Peonidin
  • Petunidin
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Phenolic acids and their esters

  • Ellagic acid - found in high concentration in raspberry and strawberry, and in ester form in red wine tannins.
  • Gallic acid - found in gallnuts, sumac, witch hazel, tea leaves, oak bark, and many other plants.
  • Salicylic acid - found in most vegetables, fruits, and herbs; but most abundantly in the bark of willow trees, from where it was extracted for use in the early manufacture of aspirin.
  • Rosmarinic acid - found in high concentration in rosemary, oregano, lemon balm, sage, and marjoram.
  • Cinnamic acid and its derivatives, such as ferulic acid - found in seeds of plants such as in brown rice, whole wheat and oats, as well as in coffee, apple, artichoke, peanut, orange and pineapple.
  • Chlorogenic acid - found in high concentration in coffee (more concentrated in robusta than arabica beans), blueberries and tomatoes. Produced from esterification of caffeic acid.
  • Chicoric acid - another caffeic acid derivative, is found only in the popular medicinal herb Echinacea purpurea.
  • Gallotannins - hydrolyzable tannin polymer formed when gallic acid, a polyphenol monomer, esterifies and binds with the hydroxyl group of a polyol carbohydrate such as glucose.
  • Ellagitannins - hydrolyzable tannin polymer formed when ellagic acid, a polyphenol monomer, esterifies and binds with the hydroxyl group of a polyol carbohydrate such as glucose.


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Other nonflavonoid phenolics


Other (someone please classify):

  • Other plant pigments such as anthoxanthins and betacyanins. (Are these antioxidants? Are they flavonoids?)
  • Silymarin - mixture of flavonolignans extracted from milk thistle.
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Other organic antioxidants

  • Lignan - antioxidant and phytoestrogen found in oats, flax seeds, pumpkin seeds, sesame seeds, rye, soybeans, broccoli, beans, and some berries.
  • Antinutrients - strong antioxidants that readily bind to needed dietary minerals, rendering them unabsorbable in the gastrointestinal tract. Examples: oxalic acid and phytic acid.


All cells use antioxidants manufactured within the organism to protect themselves from damage by free radicals. Important examples include:

  • Superoxide dismutase, a class of closely related proteins found in almost all living cells and mitochondria, and in extracellular fluids. Each molecule of superoxide dismutase contains atoms of copper, zinc, manganese or iron. Superoxide dismutase protects cells by catalysing the breakdown of the highly active superoxide ion, O2−, into oxygen and hydrogen peroxide.
  • Catalase, a widely occurring enzyme containing four iron atoms in a 500 amino acid protein. Catalase catalyses the conversion of hydrogen peroxide to water and oxygen at rates of up to 6,000,000 molecules per minute. Catalase has a secondary role oxidising toxins including formaldehyde, formic acid and alcohols.
  • Bilirubin, a breakdown product of blood, has been identified [9] as a possibly significant antioxidant.
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Beverages and foods highest in antioxidants

Image:Foods highest in antioxidants.jpg

#1 Undutched cocoa powder

#2 Dark, semisweet chocolate; particularly that which is 85% cocoa solids

#3 White tea

#4 Green rooibos

#5 Green tea

#6 Red rooibos

#7 Oolong tea

#8 Black tea

Certain fruits and berries, especially:

#9 Blueberry (especially wild blueberry; AKA bilberry) contain more antioxidants than any other fruit or vegetable, when compared on the basis of equal calories. They are high in anthocyanins, chlorogenic acid, ellagic acid, catechins, and resveratrol.

Leafy, dark green cruciferous vegetables:

  • Broccoli and all cruciferous vegetabels are high in lutein, sulforaphane (a type of glucosinate), indoles, carotenoids, beta-carotene, zeaxanthin.
  • Brussels sprouts – high in glucosinates
  • Cabbage (both red and green)
  • Kale

Certain other vegetables, especially:

  • Artichokes
  • Asparagus
  • Avocado
  • Beans
  • Beets
  • Carrots
  • Red peppers
  • Russet potatoes
  • Spinach – high in carotenoids, especially zeaxanthin (related to lutein); but also high in the antioxidant antinutrient oxalic acid
  • Tomatoes, especially ripe red tomatoes – high in the extremely potent antioxidant known as lycopene. Eating tomatoes with olive oil helps in assimilation of the lycopene. Tomatoes are also high in beta carotene and lutein. Even ketchup has some lycopene (but is also high in corn syrup, so don't go crazy).
  • Olives in the form of extra virgin olive oil. Besides being high in polyphenols, extra virgin olive oil is also high in oleic acid, an omega-9 monounsaturated fatty acid. Some studies suggest that olive oil can reduce blood pressure, reduce LDL, and ward off cancer.

Generally, the deeper and richer the color of fruits and vegetables, the higher the quantity of antioxidants. Many fruits and vegetables are also high in fiber, minerals, and vitamins. Note, however, that the most commonly eaten fruits and vegetables (apples, bananas, iceberg lettuce, and potatoes) are not on the list. Fruit juice can contain some antioxidants, but not nearly as much as the fruit from which they are made (antioxidants are concentrated in the skins and pulps), and fruit juice tends to consist primarily of corn syrup and water. To consume the greatest quantity of antioxidants, try to eat a variety of foods, and buy fruits and vegetables locally when they are in season.

Note that the color rule of thumb does not apply to varieties of tea. The darker the variety of tea, the lower is its antioxidant concentration.

Nuts, especially:

  • Walnuts
  • Pecans
  • Hazelnuts

Besides being high in polyphenols, nuts are also high in beneficial, unsaturated fatty acids. There is a correlation between nut consumption and a reduced incidence of ischemic heart disease. This is most likely due partly to the favorable lipid content and partly to the high polyphenol content. Walnuts have the highest phenolic content, which is why they taste bitterer than pecans and hazelnuts. To help preserve the antioxidants in nuts, keep them in a freezer. They have almost no water, so the freezer won’t harm them.

Certain herbs and spices. Even though people typically use spices in small amounts, some spices have extremely high antioxidant content per unit mass, especially:

  • Allspice
  • Cinnamon
  • Cloves
  • Ginger
  • Lemon balm
  • Oregano
  • Peppermint
  • Rosemary
  • Sage
  • Thyme

Tea, esp. white tea - high in polyphenols and tannins.

Seeds and grains, especially:

  • Sunflower seeds
  • Oats – high in lignans (one type of phytoestrogen, the other type being isoflavones), caffeic acid (may be carcinogenic, but its phenethyl ester may be anticarcinogenic), and ferulic acid. Also contains omega-3 fatty acids.

Other plants:

  • Cacao and chocolate – high in flavonoid polyphenols. The darker and more bitter the chocolate, the higher the concentration of polyphenols.
  • Dog rose


List of the 20 foods with the highest concentration of antioxidants (“total antioxidant capacity”), according to the USDA:

  • 01. Small red beans
  • 02. Wild blueberries
  • 03. Red Kidney beans
  • 04. Pinto beans
  • 05. Cultivated Blueberries
  • 06. Cranberries
  • 07. Artichokes
  • 08. Blackberries
  • 09. Prunes
  • 10. Raspberries
  • 11. Strawberries
  • 12. Red Delicious & Granny Smith apples
  • 13. Pecans
  • 14. Sweet cherries
  • 15. Black plums
  • 16. Russet potatoes
  • 17. Black beans
  • 18. Plums
  • 19. Gala apples
  • 20. Walnuts


Foods that score well in Oxygen Radical Absorbance Capacity:

  • Beets
  • Brussels sprouts
  • Kale
  • Spinach
  • Many of the same berries that have high Total Antioxidant Capacity.
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Antioxidants in walnuts

Analyses of walnut extracts show that walnuts:

  • Are the only nut containing high quantities of ellagic acid.
  • Are unique among the edible tree nuts because of their high content of omega-3 polyunsaturated linoleic and linolenic fatty acids. These fatty acids are short-chain fatty acids that tend to oxidize easily, so the walnut has high quantities of antioxidants to protect itself (which results in protection of LDL oxidation in humans who eat them).
  • Have a high content of tocopherols (vitamin E) in the kernel, especially gamma tocopherol.
  • Have a high content of phenolic antioxidants. These are what make the walnut taste bitter, and are found in the highest concentration in the pellicle. Some of these nonflavonoid phenolics are present as the monomers ellagic acid, gallic acid and methyl gallate, but most of these phenolics in the walnut are nonflavonoid phenolic polymers known as ellagitannins. These are hydrolyzable tannins formed when phenolic monomers bind to sugar molecules and form polymers, such as valoneic acid dilactone and pedunculagin.
  • Contain at least one flavonol, related to quercetin.
  • Are potent inhibitors of plasma and LDL oxidation, (but only under certain circumstances).

The identities of all of the chemicals found in walnut extract, and their capacity and functionality as antioxidants, are still not completely known. When walnut extract is compared to purified chemicals known to exist in the extract, the results sometimes seem to contradict each other (for example, extract has more antioxidant activity under some circumstances and less under other circumstances).

Consumption of walnuts improves one’s serum lipid profile:

  • Increases HDL cholesterol
  • Increases apolipoprotein
  • Decreases total and LDL cholesterol
  • Decreases triglycerides
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Antioxidants in fuels

Some antioxidants are added to liquid industrial chemicals, most often fuels and lubricants to prevent oxidation, and in gasolines to prevent polymerization leading to gumming. Some examples are:

Antioxidants are frequently used together with metal deactivators and corrosion inhibitors.

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References

  • Halliwell B. 1999. Antioxidant defense mechanisms: from the beginning to the end (of the beginning). Free Radical Research 31:261-72.
  • Rhodes C.J. Book: Toxicology of the Human Environment - the critical role of free radicals, Taylor and Francis, London (2000).
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External links

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