Did You Know Just That Many Cancers Are Linked To A Vitamin Deficiency?
Antioxidant
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An antioxidant is a chemical that reduces the rate of particular
oxidation reactions in a specific context, where oxidation
reactions are chemical reactions that involve the transfer
of electrons from a substance to an oxidising agent.
Antioxidants
are particularly important in the context of organic chemistry
and biology: all living cells contain complex systems of
antioxidant chemicals and/or enzymes to prevent chemical
damage to the cells' components by oxidation. The importance
and complexity of antioxidants in biology is reflected in
a medical literature of more than 142,000 scholarly articles
[1].
A
diet containing polyphenol antioxidants from plants is required
for the health of most mammals, since plants are an important
source of organic antioxidant chemicals. Antioxidants are
widely used as ingredients in dietary supplements that are
used for health purposes such as preventing cancer and heart
disease. However, while many studies have suggested benefits
for individual antioxidant supplements, several large clinical
trials have failed to clearly demonstrate a benefit for
the formulations tested, and excess supplementation may
be harmful. It is logical to assume that a one dimensional
approach to dietary supplementation with one specific antioxidant
is not a panacea, since a broad diet rich in phytonutrients
will yield thousands of different polyphenol antioxidants
available for metabolism.
Contents
1 History
2 Antioxidants in biology
3 Applications in nutrition and medicine
3.1 How antioxidants preserve health
3.2 How some antioxidants can harm health
3.3 Calorie restriction and reduced oxidative stress
3.4 Exercise and antioxidants
3.5 Clinical trials of antioxidant supplements
4 Antioxidants in food industry - Food preservatives
5 Nutritional antioxidants
5.1 Vitamins
5.2 Vitamin cofactors and minerals
5.3 Hormones
5.4 Carotenoid terpenoids
5.5 Non-carotenoid terpenoids
5.6 Flavonoid polyphenolics (also known as bioflavonoids)
5.7 Phenolic acids and their esters
5.8 Other nonflavonoid phenolics
5.9 Other organic antioxidants
6 Beverages and foods highest in antioxidants
7 Antioxidants in fuels
8 See also
9 References
10 External links
History
The term antioxidant (also "antioxygen") originally
referred specifically to a chemical that prevented the consumption
of molecular oxygen. In the 19th and early 20th century,
antioxidants were the subject of extensive research in industrial
processes such as the corrosion of metals, explosions, the
vulcanization of rubber, and the knocking of fuels in internal
combustion engines (Mattill 1947).
Early
nutrition researchers focused on the use of antioxidants
for preventing the oxidation of unsaturated fats (which
made them rancid). Antioxidant activity could be measured
simply by placing the fat in a closed glass container with
oxygen and observing the rate of oxygen consumption. However,
it was the identification of vitamins A, C, and E as antioxidants
that revolutionized the field and led to the realization
of the importance of antioxidants in biology.
The
possible mechanisms for the action of antioxidants was first
explored thoroughly by Moreau and Dufraisse (1926), who
recognized that a substance with anti-oxidative activity
is likely to be one that is itself a target for oxidation.
Research into how Vitamin E prevents the process of lipid
peroxidation led to the current understanding of antioxidants
as reducing agents that break oxidative chain reactions,
often by scavenging reactive oxygen species before they
can cause damage to the cells (Wolf 2005).
Antioxidants in biology
Living organisms all contain complex systems of antioxidant
enzymes and chemicals. Some of these systems, like the thioredoxin
system, are conserved through all of evolution and are required
for life. Antioxidants in biological systems have multiple
purposes, including defending against oxidative damage and
participating in the major signaling pathways of the cells.
One
major action of antioxidants in cells is to prevent damage
due to the action of reactive oxygen species. Reactive oxygen
species include hydrogen peroxide (H2O2), the superoxide
anion (O2-), and free radicals such as the hydroxyl radical
(•OH). These molecules are unstable and highly reactive,
and can damage cells by chemical chain reactions such as
lipid peroxidation, or formation of DNA adducts that could
cause cancer-promoting mutations or cell death. All cells
therefore contain antioxidants that serve to reduce or prevent
this damage.
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.
Antioxidants
are especially important in the mitochondria of eukaryotic
cells, since the use of oxygen as part of the process for
generating energy produces reactive oxygen species. The
process of aerobic metabolism requires oxygen because oxygen
serves as the final resting place for electrons generated
by the oxidation steps of the citric acid cycle (i.e. oxygen
is the final "electron acceptor" of the redox
reactions). However, the superoxide anion is produced as
a by-product of this reduction of oxygen in the electron
transport chain. Specifically, the reduction of coenzyme
Q in complex III is the major source of superoxide anion,
since a highly reactive free radical is formed as an intermediate
(Q•-). This unstable radical can lead to electron "leakage":
instead of moving along the well-controlled reactions of
the electron transport chain, the electrons jump directly
to molecular oxygen, forming the superoxide anion (Finkel
and Holbrook 2000).
Important
examples of the systems that cells have evolved to tightly
regulate the redox state of the cell and to protect from
damage by reactive oxygen species include:
The
thioredoxin system, including thioredoxin and thioredoxin
reductase. Thioredoxin is a 12-kDa protein that is present
in all known living organisms except the bacteria that causes
Whipple's disease. The active site of thioredoxin consists
of two neighboring cysteines, as part of a highly conserved
CXXC motif, that can cycle between an active dithiol form
(reduced) and an oxidized disulfide form. In its active
state, thioredoxin acts as an efficient reducing agent,
scavenging reactive oxygen species and maintaining other
proteins in their reduced state. After being oxidized, the
active thioredoxin is regenerated by the action of thioredoxin
reductase, and thioredoxin reductase is in turn reduced
by NADPH (Nordberg and Arner, 2001).
The glutathione system, including glutathione, glutathione
reductase, and glutathione peroxidase. Glutathione peroxidase
is an enzyme with four selenium-containing groups that catalyze
the breakdown of hydrogen peroxide and protects lipids in
cell walls from peroxidation.
Superoxide dismutase (SOD), a class of closely related proteins
found in almost all living cells and in extracellular fluids.
Each molecule of superoxide dismutase contains atoms of
copper, zinc, manganese or iron. SOD that is formed in the
mitochondria contains manganese (MnSOD). This SOD is formed
in the matrix of the mitochondria. SOD that is formed in
the cytoplasm of the cell contains copper and zinc (CuZnSOD).
Superoxide dismutase protects cells by catalysing the breakdown
of the highly reactive superoxide anion 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.
Peroxiredoxins catalyse the reduction of hydroperoxides.
Uric Acid is the antioxidant in highest concentration in
the extracellular fluids in humans and higher primates.
It may have partially-substituted for vitamin C in human
evolution.
Applications
in nutrition and medicine
How
antioxidants preserve health
Antioxidants are chemicals that reduce oxidative damage
to cells and biochemicals. Researchers have found high correlation
between oxidative damage and the occurrence 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
may slow down, prevent, or 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 degeneration, 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.
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:
cocoa/chocolate,
spinach, and berries - oxalic acid
whole grains, maize - phytic acid
tea - tannins
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.
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.
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 [2]. 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 [3]. 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) [4]. 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.
Exercise and antioxidants
During exercise, oxygen consumption can temporarily increase
by a factor of more than 10 [5]. This leads to a temporary
large increase in the production of oxygen free radicals,
resulting in increased cell damage contributing to muscular
fatigue during and after exercise. The body uses antioxidants
to reduce the amount of such damage. The inflammatory response
that occurs after strenuous exercise is also associated
with increased occurrence of free radicals, especially during
the 24 hours after an exercise session. In this phase too,
antioxidants in the body reduces this damage. The immune
system response to damage done by exercise peaks 2 to 7
days after exercise, the period during which adaptation
resulting in greater fitness is greatest. During this process,
free radicals are used by neutrophils in the immune system
to identify damaged tissue. As a result, excessive antioxidant
levels have the potential to inhibit recovery and adaptation
mechanisms [6].
There
is a popular view that those who undertake vigorous exercise
can benefit from increased consumption of antioxidants,
but an examination of the literature finds support that
this is the case only for certain antioxidants at certain
levels, and some evidence that very large intake of some
antioxidants may be detrimental to recovery from exercise.
There is strong evidence that one of the adaptations that
result from exercise is a strengthening of the body's antioxidant
defenses, particularly the glutathione system, to deal with
the increased oxidative stress [7]. It is even possible
that this effect may be to some extent protective against
diseases which are associated with oxidative stress, which
would provide a partial explanation for the lower incidence
of several diseases and better health of those who undertake
regular exercise, but there is inadequate evidence for this
hypothesis at present.
The
antioxidant system that protects lipid membranes from free
radicals includes vitamin E, beta-carotene, vitamin A, and
coenzyme Q10. The system that scavenges free radicals in
the water based cytoplasm includes vitamin C, glutathione
peroxidase, superoxide dismutase, and catalase. The effect
of each of the exogenous antioxidants needs to be examined
separately, although they work in a co-operative manner.
The
body of research suggests no benefits from supplementing
with vitamin A above normally recommended levels. Recent
well-designed studies suggest there are no ergogenic benefits
from vitamin E (except for those who do exercise at high
altitude) [8],[9],(Mehdani et al, 1997), despite its key
role in preventing lipid membrane peroxidation. For example,
6 weeks of vitamin E supplementation had no effect on muscle
damage indicators in ultramarathon runners [10]. Although
selenium is essential to the glutathione antioxidant system
which, as mentioned above, is upregulated by exercise, there
is no evidence that supplementation with selenium above
the RDA is of any benefit. However, for vitamin C there
is considerable evidence that vitamin C requirements are
greater in those who do vigorous exercise, with plasma levels
falling with intake of 100mg (well over the accepted RDA)
and around 300mg per day being required to maintain blood
plasma levels (Keith, 1997). There is some evidence that
supplementation with vitamin C increased the amount of intense
exercise that can be done, and lowered the heart rate while
doing it (which is indicative of greater efficiency) [11],
and that vitamin C supplementation before strenuous exercise
reduces the amount of muscle damage [12]. However, some
other studies found no such effects, and some research suggests
that supplementation with amounts as high as 1000mg inhibits
recovery [13]. There is strong evidence that vitamin C supplementation
reduces upper respiratory tract infections in ultra-endurance
athletes [14].
In
summary, a diet with up to 500mg of vitamin C may be of
benefit to those who undertake high intensity or high volume
exercise, but there is little evidence that normal requirements
for vitamin A, vitamin E or selenium are increased.
Clinical trials of antioxidant supplements
Although some levels of antioxidant vitamins and minerals
in the diet are required for good health, there is considerable
doubt as to whether antioxidant supplementation is beneficial,
and if so, which and what amount of antioxidant(s) are optimal.
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.
In
the early 1990s, it was hypothesized that oxidation of LDL
cholesterol contributes to heart disease, and several observational
studies found that people taking Vitamin E supplements had
a lower risk of developing heart disease (Rimm 1993). Taken
together, this led researchers to conduct at least seven
large clinical trials testing the effects of antioxidant
supplement with Vitamin E, in doses ranging from 50 to 600
mg per day. However, none of these trials found a statistically
significant effect of Vitamin E on overall number of deaths
or on deaths due to heart disease (Vivekananthan 2003).
While
several trials have investigated supplements with high doses
of antioxidants, the "Supplementation en Vitamines
et Mineraux Antioxydants" (SU.VI.MAX) study tested
the effect of supplementation with doses comparable to those
in a healthy diet (Hercberg 2003). Over 12,500 French men
and women took either low-dose antioxidants (120 mg of ascorbic
acid, 30 mg of vitamin E, 6 mg of beta carotene, 100 µg
of selenium, and 20 mg of zinc) or placebo pills for an
average of 7.5 years. The investigators found there was
no statistically significant effect of the antioxidants
on overall survival, cancer, or heart disease. However,
a subgroup analysis showed a 31% reduction in the risk of
cancer in men, but not women. The authors interpreted these
results as suggesting that "an adequate and well-balanced
supplementation of antioxidant nutrients, at doses that
might be reached with a healthy diet that includes a high
consumption of fruits and vegetables, had protective effects
against cancer in men."
The
significant effect of supplementary selenium in reducing
incidence of prostate cancer was strongly supported by the
Nutrition for the Prevention of Cancer (NPC) trial (designed
primarily to determine the effect of selenium supplementation
on skin cancers) [15], and found significant effects for
subjects whose plasma selenium levels were in the middle
and lower thirds, but not for those in the top third. The
SELECT project further investigating the effects of selenium
supplementation (in combination with vitamin E) on prostate
cancer incidence, but final results will not be available
until 2013 [16].
Antioxidants in food industry - Food preservatives
Antioxidants used as food additives to help guard against
food deterioration include:
Ascorbic
acid (vitamin C)
Tocopherol-derived compounds
BHA, BHT, EDTA
Citric acid
Acetic acid - found in vinegar; used for pickling
Pectin
Rosmarinic acid - in the form of the herb rosemary and Italian
seasoning mixtures in naturally or minimally processed foods,
and pet foods
Nutritional
antioxidants
See also List of phytochemicals and foods in which they
are prominent
Since the discovery of vitamins, it has been recognized
that antioxidants from the diet are essential for healthful
lives in humans and many other mammals. More recently, a
large body of evidence has accumulated that suggests supplementation
of the diet with various kinds of antioxidants can improve
health and extend life. Many nutraceutical and health food
companies now sell formulations of antioxidants as dietary
supplement. These supplements may include specific antioxidant
chemicals, like resveratrol (from grape seeds), combinations
of antioxidants, like the "ACES" products that
contain beta carotene (provitamin A), vitamin C, vitamin
E and Selenium, or specialty herbs that are known to contain
antioxidants such as green tea and jiaogulan.
There
are hundreds of different types of antioxidants. The following
substances may have nutritional antioxidant effects:
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.
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.
Zinc. See Zinc's Antioxidant Potential Probed.
Manganese, particularly when in its +2 valence state as
part of the enzyme called superoxide dismutase (SOD).
Hormones
Melatonin is a natural hormone, occurring in every organism,
which has many biological roles. Melatonin acts as an antioxidant
and promoter of antioxidants in several different ways [17].
Recent research supports a specific role as an antioxidant
in mitochondria, which have an high level of reactive oxygen
species produced during aerobic metabolism, but lack some
of the protective mechanisms of cell nuclei. [18],[19],[20],[21].
Carotenoid
terpenoids
See main article at Carotenoid
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.
Canthaxantin
Non-carotenoid
terpenoids
Eugenol - has by far the highest Oxygen Radical Absorbance
Capacity (ORAC) of all foodborn substances (in clove oil)[22].
Its concentration in clove oil ranges 5-20 times greater
than where it is found in other sources[23] such as in basil
and cinnamon.
Saponins
and limonoids Editor's note: Not certain if these are antioxidants;
work in progress...
Flavonoid polyphenolics (also known as bioflavonoids)
Bioflavonoids, a subset of polyphenol antioxidants, are
present in many dark berries such as pomegranate,seabuckthorn,
noni, blueberries, and blackberries, as well as in certain
types of coffee and tea, especially green tea.
Flavonols:
Resveratrol
- found in the skins of dark-colored grapes, and concentrated
in red wine.
Pterostilbene - methoxylated analogue of resveratrol, abundant
in Vaccinium berries
Kaempferol
Myricetin - walnuts are a rich source
Isorhamnetin
Proanthocyanidins, or condensed tannins
Flavones:
Quercetin
and related, such as rutin
Luteolin
Apigenin
Tangeritin
Flavanones:
Hesperetin
(metabolizes to hesperidin)
Naringenin (metabolized from naringin)
Eriodictyol
Flavan-3-ols (anthocyanidins):
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 protect plants from UV damage:
Cyanidin
Delphinidin
Malvidin
Pelargonidin
Peonidin
Petunidin
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.
Other
nonflavonoid phenolics
Curcumin
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.
Other
organic antioxidants
Citric acid
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.
Bilirubin, a breakdown product of blood, has been identified
[24] as a possibly significant antioxidant.
Uric acid
R-a-lipoic acid - fat and water soluble
Silymarin - fat soluble; also available in water soluble
form
N-acetylcysteine - water soluble
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:
Walnut
- high concentration of ellagic acid; high concentrations
of tocopherols (especially gamma-tocopherol) in the kernel;
high concentrations of phenolic antioxidants (found in the
pellicle) such as ellagic acid, gallic acid, methyl gallate,
and ellagitannins; so much antioxidizing power preserves
its highly reactive short-chain fatty acids (especially
alpha-linolenic omega-3) from rancidity
Pecan
Hazelnut
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.
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:
AO-22
(N,N'-di-2-butyl-1,4-phenylenediamine), for turbine oils,
transformer oils, hydraulic fluids, waxes, and greases
AO-24 (mostly N,N'-di-2-butyl-1,4-phenylenediamine), blended
for low-temperature handling)
AO-29 (2,6-di-tert-butyl-4-methylphenol), for turbine oils,
transformer oils, hydraulic fluids, waxes, greases, and
gasolines
AO-30 (alkylated phenols, mostly 2,4-dimethyl-6-tert-butylphenol
(>97%)), for jet fuels and gasolines, including aviation
gasolines
AO-31 (alkylated phenols, mostly 2,4-dimethyl-6-tert-butylphenol
(>72%)), for jet fuels and gasolines, including aviation
gasolines
AO-32 (alkylated phenols, mostly 2,4-dimethyl-6-tert-butylphenol
(>55%), and 2,6-di-tert-butyl-4-methylphenol (>15%)),
for jet fuels and gasolines, including aviation gasolines
AO-36 (alkylated phenols), for gasolines
AO-37 (alkylated phenols, mostly 2,6-di-tert-butylphenol),
for jet fuels and gasolines, widely approved for aviation
fuels
Antioxidants are frequently used together with metal deactivators
and corrosion inhibitors.
See also
Free radical theory
Life extension
List of life extension related topics
Nutrition
Phytochemical
Radical Induction Theory of Ulcerative Colitis
Redox (oxidation)
References
Halliwell B. 1999. Antioxidant defense mechanisms: from
the beginning to the end (of the beginning). Free Radical
Research 31:261-72.
Hercberg S, Galan P, Preziosi P, Bertrais S, Mennen L, Malvy
D, Roussel AM, Favier A, Briancon S (2004). "The SU.VI.MAX
Study: a randomized, placebo-controlled trial of the health
effects of antioxidant vitamins and minerals". Arch
Intern Med 164 (21): 2335-42. PMID 15557412.
Finkel T, Holbrook NJ (2000). "Oxidants, oxidative
stress and the biology of ageing". Nature 408 (6809):
239-47. PMID 11089981.
Keith, R.E. Ascorbic Acid. chapter 2 in Sports Nutrition
Vitamins and Trace Minerals. Edited by Ira Wolinsky and
Judy A. Driskell. New York: CRC Press, 1997, p. 29-45
Matill HA (1947). "Antioxidants". Annu Rev Biochem
16: 177-192.
Mehdani M, Fielding RA, Fotouhi N, Vitamin E. chapter 10
in Sports Nutrition Vitamins and Trace Minerals. Edited
by Ira Wolinsky and Judy A. Driskell. New York: CRC Press,
1997, 119-131
Nordberg J, Arner ES (2001). "Reactive oxygen species,
antioxidants, and the mammalian thioredoxin system".
Free Radic Biol Med 31 (11): 1287-312. PMID 11728801.
Rhodes C.J. Book: Toxicology of the Human Environment -
the critical role of free radicals, Taylor and Francis,
London (2000).
Rimm EB, Stampfer MJ, Ascherio A, Giovannucci E, Colditz
GA, Willett WC (1993). "Vitamin E consumption and the
risk of coronary heart disease in men". N Engl J Med
328 (20): 1450-6. PMID 8479464.
Vivekananthan DP, Penn MS, Sapp SK, Hsu A, Topol EJ (2003).
"Use of antioxidant vitamins for the prevention of
cardiovascular disease: meta-analysis of randomised trials".
Lancet 361 (9374): 2017-23. PMID 12814711.
Wolf G (2005). "The discovery of the antioxidant function
of vitamin E: the contribution of Henry A. Mattill".
J Nutr 135 (3): 363-6. PMID 15735064.
http://en.wikipedia.org/
wiki/Antioxidant
