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Antioxidants
Mgr. Iva Klimešová, Ph.D.
• Antioxidant is any substance that prevents or
reduces damage caused by reactive free
radicals.
• Free radicals are formed primarily in the body
during normal metabolism and also upon
exposure to environmental factors such as
cigarette smoke or pollutants.
• Fats, which are an integral part of all cell
membranes, are vulnerable to destruction
through oxidation by free radicals.
• Free radicals promote beneficial oxidation that
produces energy and kills bacteria.
• In excess, however, they produce harmful oxidation
that can damage cell membranes and cell contents.
• Although oxidation reactions are critical for life, they can
also be damaging; hence, plants and animals maintain
complex systems of multiple types of antioxidants, such
as glutathione, vitamin C, and vitamin E as well as
enzymes such as catalase, superoxide dismutase and
various peroxidases.
• Low levels of antioxidant molecules or inhibition of these
antioxidant enzymes causes oxidative stress and may
damage or kill cells.
• It is known that people who eat adequate amounts of
fruits and vegetables high in antioxidants have a lower
incidence of cardiovascular disease, certain cancers,
and cataracts.
The most publicized antioxidants
have been:
• fat-soluble antioxidants: vitamin A and
carotenoids, vitamin E, Coenzyme Q10
• water-soluble antioxidants: vitamin C,
minerals – zinc, selenium, manganese
Vitamin A
Vitamin A is a generic term for a large number of related
compounds:
• Retinol (an alcohol) and retinal (an aldehyde) are often
referred to as preformed vitamin A. Retinol, retinal,
retinoic acid, and related compounds are known as
retinoids.
• Beta-carotene and other carotenoids that can be
converted by the body into retinol are referred to as
provitamin A.
• Hundreds of different carotenoids are synthesized by
plants, but only about 10% of them are provitamin A.
• The main function of vitamin A in humans appears to be
that of an antioxidant, beta-carotene has stronger
antioxidant activity than retinol.
• Beta-carotene is less easily absorbed
than retinol and must be converted to
active form.
• Two micrograms (mcg) of beta-carotene in
oil provided as a supplement can be
converted by the body to 1 mcg of retinol.
• However, 6 mcg of beta-carotene from
foods are required to provide the body
with 1 mcg of retinol.
• Retinol is found in foods from animals.
Plants contain carotenoids.
good sources, (RDA = 1000 mcg, or 5000 IU, for adult
males and 800 mcg, or 4,000 IU, for adult females)
Food
Serving
Vitamin A,
Vitamin A,
IU
Cod liver oil
1 teaspoon
1,350 mcg
4,500 IU
Fortified breakfast cereals
1 serving
150-230 mcg
500-767 IU
Egg
1 large
91 mcg
303 IU
Butter
1 tablespoon
97 mcg
323 IU
Whole milk
1 cup (8 fl
ounces)
68 mcg
227 IU
Carrot (raw)
1/2 cup,
chopped
385 mcg
1,283 IU
Spinach
1/2 cup,
cooked
472 mcg
1,572 IU
Squash, butternut
1/2 cup,
cooked
572 mcg
1,906 IU
• The combination of vitamin A and iron seems to
reduce anemia more effectively than either iron or
vitamin A alone.
• Toxicity:
• Vitamin A toxicity is relatively rare. Symptoms
include nausea, headache, fatigue, loss of
appetite, dizziness, and dry skin.
• Consumption of excess vitamin A during
pregnancy is known to cause birth defects.
Carotenoids
• The main carotenoids: Alpha-Carotene, Beta-Carotene, BetaCryptoxanthin, Lycopene, Lutein and Zeaxanthin
• Carotenoids are yellow, orange, and red pigments synthesized
by plants.
• Fruits and vegetables provide most of the carotenoids in the human
diet.
• Orange and yellow vegetables like carrots and winter squash are
rich sources of alpha- and beta-carotene. Spinach is also a rich
source of beta-carotene, although the chlorophyll in spinach leaves
hides the yellow-orange pigment.
• Alpha-carotene, beta-carotene, and beta-cryptoxanthin are
provitamin A, meaning they can be converted by the body to retinol
(vitamin A).
• Lutein, zeaxanthin, and lycopene have no vitamin A activity.
• For dietary carotenoids to be absorbed
intestinally, they must be mixed with fatty
acids and incorporated into micelles.
• As little as 3-5 g of fat in a meal appears
sufficient to ensure carotenoid absorption.
• Supplement: Because they do not need to be
released from the plant matrix, carotenoids
supplements (in oil) are more efficiently
absorbed than carotenoids in foods.
The vitamin A activity of beta-carotene in foods is 1/6 that of retinol (preformed
vitamin A). Thus, it would take 6 mcg of beta-carotene from foods to provide
the equivalent of 1 mcg of retinol.
Beta-Carotene Content of Selected Foods
Food
Serving
Beta-Carotene (mcg)
Carrot juice
1 cup (8 fl oz)
21,955
Pumpkin, canned
1 cup
17,003
Sweet potato, baked
1 medium
16,803
Spinach, frozen, cooked
1 cup
13,750
Carrots, cooked
1 cup
12,998
Collards, frozen, cooked
1 cup
11,591
Kale, frozen, cooked
1 cup
11,470
Pumpkin pie
1 piece
7,366
Dandelion greens, cooked
1 cup
6,248
Winter squash, cooked
1 cup
5,726
Cantaloupe, raw
1 cup
3,232
• Supplementation: Although diets rich in
beta-carotene have generally been
associated with reduced cardiovascular
disease risk in observational studies,
there is no evidence that beta-carotene
supplementation reduces
cardiovascular disease risk.
• Toxicity: Two randomized controlled trials
found that high-dose beta-carotene
supplements increased the risk of lung
cancer in smokers.*
* Michaud DS, Feskanich D, Rimm EB, et al. Intake of specific carotenoids and risk of lung cancer in 2 prospective US cohorts. Am J Clin Nutr.
2000;72(4):990-997.
Holick CN, Michaud DS, Stolzenberg-Solomon R, et al. Dietary carotenoids, serum beta-carotene, and retinol and risk of lung cancer in the
alpha-tocopherol, beta-carotene cohort study. Am J Epidemiol. 2002;156(6):536-547.
Vitamin E
• Major sources of alpha-tocopherol in the diet
include vegetable oils (olive, sunflower,
safflower oils), nuts, whole grains, and green
leafy vegetables.
• The main function of alpha-tocopherol in
humans appears to be that of an antioxidant.
• The term vitamin E describes a family of eight
antioxidants:
– four tocopherols, alpha-, beta-, gamma- and delta-,
– and four tocotrienols (also alpha-, beta-, gammaand delta-).
• Alpha-tocopherol is the only form of vitamin E
that is actively maintained in the human body.
good sources
(the RDA for vitamin E was previously 8 mg/day for women
and 10 mg/day for men)
Food
Serving
Alpha-tocopherol (mg)
Olive oil
1 tablespoon
1.9
Soybean oil
1 tablespoon
1.2
Corn oil
1 tablespoon
1.9
Canola oil
1 tablespoon
2.4
Safflower oil
1 tablespoon
4.6
Sunflower oil 1 tablespoon
5.6
Almonds
1 ounce (30 g)
7.3
Hazelnuts
1 ounce (30 g)
4.3
Peanuts
1 ounce (30 g)
2.4
Spinach
½ cup, raw chopped
1.8
Carrots
½ cup, raw chopped
0.4
Avocado
1 medium
3.4
• Toxicity: High-dose vitamin E
supplementation increases the risk of
hemorrhage.
• Supplementation with 400 IU/day of
vitamin E has been found to accelerate the
progression of retinitis pigmentosa.
Coenzyme Q10 (ubiquinol)
• Coenzyme Q10 is a fat-soluble compound
primarily synthesized by the body and also
consumed in the diet.
• Coenzyme Q10 is a member of the ubiquinone
family of compounds, also known as ubiquinone
or ubiquinol.
• All animals, including humans, can
synthesize ubiquinones, hence, coenzyme
Q10 cannot be considered a vitamin.
• Coenzyme Q10 is required for mitochondrial
ATP synthesis and functions as an antioxidant in
cell membranes and lipoproteins.
• CoQ10 has been widely used for the treatment of heart
disease (especially heart failure), gum diseases, and
also breast cancer.
• Young people are able to make Q10 from the lower
numbered ubiquinones such as Q6 or Q8. The sick and
elderly may not be able to make enough.
• Rich sources of dietary coenzyme Q10 include mainly
meat, poultry, and fish. Other relatively rich sources
include soybean and canola oils, and nuts. Fruits,
vegetables, eggs, and dairy products are reasonable
sources of coenzyme Q10.
• Approximately 14%-32% of coenzyme Q10 was lost
during frying of vegetables and eggs, but the coenzyme
Q10 content of these foods did not change when they
were boiled.
good sources
Food
Serving
Coenzyme Q10(mg)
Beef, fried
3 ounces
2.6
Herring, marinated
3 ounces
2.3
Chicken, fried
3 ounces
1.4
Soybean oil
1 tablespoon
1.3
Canola oil
1 tablespoon
1.0
Rainbow trout, steamed
3 ounces
0.9
Peanuts, roasted
1 ounce
0.8
Sesame seeds, roasted
1 ounce
0.7
Pistachio nuts, roasted
1 ounce
0.6
Broccoli, boiled
1/2 cup, chopped
0.5
Cauliflower, boiled
1/2 cup, chopped
0.4
Orange
1 medium
0.3
Egg, boiled
1 medium
0.1
• Supplementation: Although coenzyme
Q10 supplements are relatively safe, they
may decrease the anticoagulant efficacy of
warfarin. Presently, it is unclear whether
individuals taking cholesterol-lowering
medications, known as statins, would
benefit from coenzyme Q10
supplementation.
Vitamin C
• Sources: fruits and vegetables vary in their
vitamin C content
• Vitamin C, also known as ascorbic acid, is a
water-soluble vitamin.
• Unlike most mammals, humans do not have
the ability to make their own vitamin C.
Therefore, we must obtain vitamin C through our
diet.
• Vitamin C is known as a highly effective
antioxidant in living organisms.
good sources
(RDA – 80 mg)
Food
Serving
Vitamin C (mg)
Orange juice
¾ cup (6 ounces)
75
Grapefruit juice
¾ cup (6 ounces)
60
Orange
1 medium
70
Grapefruit
½ medium
44
Strawberries
1 cup, whole
82
Tomato
1 medium
23
Sweet red pepper
½ cup, raw chopped
Broccoli
½ cup, cooked
58
Potato
1 medium, baked
26
141
Supplements: Vitamin C (ascorbic acid) is available in many
forms, but there is little scientific evidence that any one
form is better absorbed or more effective than another.
Natural vs. synthetic vitamin C:
•
Natural and synthetic ascorbic acid are chemically
identical and there are no known differences in their
biological activities or bioavailability
Toxicity: A number of possible problems with very large
doses of vitamin C have been suggested, mainly based
on in vitro experiments or isolated case reports,
including: genetic mutations, birth defects, cancer,
atherosclerosis, kidney stones, increased oxidative
stress, excess iron absorption, vitamin B-12 deficiency,
and erosion of dental enamel.
•
However, none of these adverse health effects have
been confirmed, and there is no reliable scientific
evidence that large amounts of vitamin C (up to 10
grams/day in adults) are toxic.
Zinc
Shellfish, beef, and other red meats are rich sources of
zinc.
Nuts and legumes are relatively good plant sources.
• Zinc bioavailability is relatively high in meat, eggs, and
seafood because of the relative absence of compounds
that inhibit zinc absorption and the presence of certain
amino acids (cysteine and methionine) that improve zinc
absorption.
• The zinc in whole grain products and plant proteins
is less bioavailable due to their relatively high content
of phytic acid, a compound that inhibits zinc absorption.
• The enzymatic action of yeast reduces the level of
phytic acid in foods. Therefore, leavened whole grain
breads have more bioavailable zinc than unleavened
whole grain breads.
good sources
(RDA: 15 mg for men, 12 mg for women)
Food
Serving
Zinc (mg)
Oysters
6 medium (cooked)
43.4
Crab, Dungeness
3 ounces (cooked)
4.6
Beef
3 ounces (cooked)
5.8
Pork
3 ounces (cooked)
2.2
Chicken (dark meat)
3 ounces (cooked)
2.4
Turkey (dark meat) 3 ounces (cooked)
3.5
Yogurt, fruit
1 cup (8 ounces)
1.8
Cheese, cheddar
1 ounce
0.9
Milk
1 cup (8 ounces)
1.0
Cashews
1 ounce
1.6
Almonds
1 ounce
1.0
Peanuts
1 ounce
0.9
Beans, baked
1/2 cup
1.8
• Supplementation: A number of zinc supplements are
available, including zinc acetate, zinc gluconate, zinc
picolinate, and zinc sulfate.
• Zinc picolinate has been promoted as a more
absorbable form of zinc, but there is little data to
support this idea in humans.
• Adverse effects: The major consequence of long-term
consumption of excessive zinc is copper deficiency.
• Drug Interactions: Zinc may decrease absorption of the
antibiotic. Taking zinc supplements and these antibiotics
at least two hours apart should prevent this interaction.
Selenium
• The richest food sources of selenium are organ meats
and seafood, followed by muscle meats.
• In general, there is wide variation in the selenium content
of plants and grains because plants do not appear to
require selenium.
• Thus, the incorporation of selenium into plant proteins is
dependent only on soil selenium content. Brazil nuts
grown in areas of Brazil with selenium-rich soil may
provide more than 100 mcg of selenium in one nut, while
those grown in selenium-poor soil may provide 10 times
less.
• Selenium is a trace element that is essential in small
amounts, but can be toxic in larger amounts.
• Humans and animals require selenium for the function of
a number of selenium-dependent enzymes, also known
as selenoproteins (e.g. coating of sperm is made from
selenoproteins).
good sources
Food
(RDA: 70 mcg for men, 55 mcg for women)
Serving
Selenium (mcg)
839 (above the tolerable
Brazil nuts (from
selenium-rich soil)
1 ounce (6-8
kernels)
Shrimp
3 ounces (10-12)
34
Crab meat
3 ounces
40
Salmon
3 ounces
40
Halibut
3 ounces
40
Noodles, enriched
1 cup, cooked
35
Rice, brown
1 cup, cooked
19
Chicken (light meat)
3 ounces
20
Pork
3 ounces
33
Beef
3 ounces
17
Whole wheat bread
2 slices
15
Milk
8 ounces (1 cup)
5
Walnuts
1 ounce, shelled
5
upper intake level of 400
mcg/day)
• Supplementation: Selenium supplements are
available in several forms.
• Sodium selenite and sodium selenate are
inorganic forms of selenium.
• Selenate is almost completely absorbed, but a
significant amount is excreted in the urine before it
can be incorporated into proteins.
• Selenite is only about 50% absorbed, but is better
retained than selenate, once absorbed.
• Selenomethionine, an organic form of selenium
that occurs naturally in foods, is about 90%
absorbed (enriched are yeast, which are also
available as supplements).
• It is not clear whether one form of selenium is
preferable to another.
• Toxicity: Although selenium is required
for health, high doses can be toxic.
Manganese
• Rich sources of manganese include whole grains, nuts,
leafy vegetables, and teas.
• Foods high in phytic acid, such as beans, seeds, nuts,
whole grains, and soy products, or foods high in oxalic
acid, such as cabbage, spinach, and sweet potatoes, may
slightly inhibit manganese absorption.
• Although teas are rich sources of manganese, the tannins
present in tea may moderately reduce the absorption of
manganese
• Manganese is a mineral element that is both nutritionally
essential and potentially toxic.
good sources
(RDA: 2-5 mg)
Food
Serving
Manganese (mg)
Pineapple, raw
1/2 cup, diced
1.28
Pineapple juice
1/2 cup (4 ounces)
1.24
Pecans
1 ounce
1.12
Almonds
1 ounce
0.74
Peanuts
1 ounce
0.59
Brown rice, cooked 1/2 cup
0.88
Whole wheat bread
1 slice
0.65
Beans, cooked
1/2 cup
0.48
Spinach, cooked
1/2 cup
0.84
Tea (green)
1 cup (8 ounces)
0.41-1.58
Tea (black)
1 cup (8 ounces)
0.18-0.77
• Supplements: Several forms of manganese are
found in supplements, including manganese
gluconate, manganese sulfate, manganese
ascorbate, and amino acid chelates of
manganese.
• Relatively high levels of manganese ascorbate
may be found in a bone/joint health product
containing chondroitin sulfate and glucosamine
hydrochloride
• Toxicity: A single case of manganese toxicity
was reported in a person who took large
amounts of mineral supplements for years, while
another case was reported as a result of taking a
Chinese herbal supplement.
• Some antioxidants are made in the body and
are poorly absorbed from the intestine.
• One example is glutathione, which is made
from amino acids. Glutathion as a supplemet in
the gut is broken down and have little effect on
the concentration of glutathione in the body.
• Ubiquinol (coenzyme Q) is also poorly absorbed
from the gut and is made in humans body.
Food preservatives
• Antioxidants are used as food additives to help guard
against food deterioration.
• Exposure to oxygen and sunlight are the two main factors
in the oxidation of food, so food is preserved by keeping in
the dark and sealing it in containers or even coating it in
wax, as with cucumbers.
• However, as oxygen is also important for plant respiration,
storing plant materials in anaerobic conditions produces
unpleasant flavours and unappealing colours.
• Consequently, packaging of fresh fruits and vegetables
contains an -8% oxygen atmosphere.
• Some antioxidants are added to industrial products. A
common use is as stabilizers in foods and lubricants to
prevent oxidation.
• Antioxidant preservatives are also added to fat-based
cosmetics such as lipstick and moisturizers to prevent
rancidity.
• The body has a limited ability to excrete vitamins and
minerals, so excessive consumption may cause a
number of health problems, even in relatively small
dosages.
• Vitamin supplements may be necessary for individuals
whose diets don't provide the recommended amounts of
specific vitamins and especially important for pregnant
and nursing women and people with specific illnesses.
• However, the benefits of vitamin supplements for the
general population remain uncertain.