Antioxidants Iva Rehov

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AntioxidantsIva Rehová
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• 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.

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• 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.

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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

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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.

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• 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.

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good sources, (RDA 1000 mcg, or 5000 IU, for
adult males and 800 mcg, or 4,000 IU, for adult
females)
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• 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.

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Carotenoids

• The main carotenoids Alpha-Carotene,
  Beta-Carotene, Beta-Cryptoxanthin, 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.

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• 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.

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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.
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• 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.
200072(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.
2002156(6)536-547.
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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-, gamma-
  and delta-).
• Alpha-tocopherol is the only form of vitamin E
  that is actively maintained in the human body.

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good sources (the RDA for vitamin E was
previously 8 mg/day for women and 10 mg/day for
men)
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• 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.

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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.

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• 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.

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good sources
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• 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.

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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.

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good sources (RDA 80 mg)
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• 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.

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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.

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good sources (RDA 15 mg for men, 12 mg for
women)
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• 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.

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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).

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good sources (RDA 70 mcg for men, 55 mcg for
women)
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• 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.

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• Toxicity Although selenium is required for
  health, high doses can be toxic.

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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.

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good sources (RDA 2-5 mg)
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• 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.

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• 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.

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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.

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• 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.