The science of nutrition 4th edition thompson manore vaughan chapter 10

Chapter 10 Lecture

Chapter 10:
Nutrients Involved
in Antioxidant
Function
and Vision

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What Are Antioxidants?
• Compounds that protect cells from the damage
caused by oxidation
• Hence, "anti"-oxidation
• Some nutrients with antioxidant properties:
• Vitamin E
• Vitamin C
• Vitamin A (precursor beta-carotene)
• Selenium

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Exchange Reactions
• Oxidation is a chemical reaction in which atoms
lose electrons
• Reduction occurs when atoms gain an electron
• Oxidation-reduction reactions typically result in
an even exchange of electrons, called exchange
reactions.

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© 2017 Pearson Education, Inc.


Free Radicals
• Stable atoms have an even number of electrons
(pairs) orbiting
• Electron loss during oxidation leaves an odd
number or unpaired electron
• Unstable atoms are called free radicals
• Reactive oxygen species (ROS): oxygen
molecule that becomes a free radical

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© 2017 Pearson Education, Inc.


What Causes Free Radicals?
• Metabolic processes
• Ex: immune system fighting infections
• Environmental factors
• Pollution
• Excess sunlight
• Toxic substances
• Radiation

• Tobacco smoke
• Asbestos

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Free Radical Damage
• Can destabilize other molecules and damage
cells
• Cell membrane damage:
• Free radicals form within the phospholipid
bilayers of cell membranes and "steal"
electrons
• Damaged lipid molecules cause cell
membrane to lose its integrity
• Causes damage to the cell and all systems
affected by the cell
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© 2017 Pearson Education, Inc.


Diseases Linked with Free Radicals
• Free radicals damage low-density lipoproteins
(LDLs), cell proteins, and DNA
• Increase risk for chronic diseases, including:
• Cancer
• Heart disease
• Type 2 diabetes

• Arthritis
• Cataracts
• Alzheimer's and Parkinson's diseases

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How Do Antioxidants Work?
• Stabilize free radicals or oppose oxidation
• Antioxidant vitamins donate their electrons or
hydrogen molecules to free radicals to stabilize
them and reduce oxidation damage
• Antioxidant minerals act as cofactors within
enzyme systems that convert free radicals to
less damaging substances that can be excreted
• Phytochemicals help stabilize free radicals and
prevent damage to cells and tissues

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Antioxidant Enzymes
• Antioxidant enzymes/enzyme systems:
• Convert free radicals to less damaging
substances
• Break down oxidized fatty acids that have
become oxidized
• Make more vitamin antioxidants available to
fight other free radicals

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Antioxidant Enzymes (continued)
• Antioxidant enzymes:
• Superoxide dismutase converts free radicals
to less damaging substances, such as
hydrogen peroxide
• Catalase removes hydrogen peroxide from
the body
• Glutathione peroxidase removes hydrogen
peroxide

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Nutrients as Antioxidants
• Certain compounds stabilize free radicals and
prevent damage to cells and tissues
• Nutrients with antioxidant properties include:
• Vitamin E
• Vitamin C
• Beta-carotene (phytochemical and precursor
to vitamin A)
• Vitamin A
• Selenium

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© 2017 Pearson Education, Inc.


Vitamin E
• Fat soluble, absorbed with dietary fats
• Incorporated into the chylomicron to be
transported to the liver
• Incorporated into very-low-density lipoproteins
(VLDLs) and is a part of low-density lipoproteins
(LDLs)
• 90% of vitamin E is stored in adipose tissue, the
rest in cell membranes

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Forms of Vitamin E
• Two families of compounds: tocotrienols and
tocopherols.
• Tocopherol compounds are the biologically
active forms
• Alpha-tocopherol is most active (potent), found
in food and supplements
• RDA: expressed as alpha-tocopherol (mg/day)
• Food labels and supplements: expressed as
alpha-tocopherol equivalents and International
Units (IU)
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© 2017 Pearson Education, Inc.


Functions of Vitamin E
• Protects polyunsaturated fatty acids (PUFAs),
fatty cell components, and LDLs from oxidization
(lower heart disease risk)
• Protects red blood cell membranes and lung
cells
• Anticoagulant properties, opposes excessive clot
formation
• Normal nerve and muscle development in early
life
• Enhances immune system
• Improves vitamin A absorption, if intake is low
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RDA for Vitamin E
• RDA: 15 mg alpha-tocopherol per day
• Determined to be sufficient to prevent
erythrocyte hemolysis, rupturing (lysis) of red
blood cells (erythrocytes)
• Tolerable Upper Intake Level (UL): 1,000 mg
alpha-tocopherol per day

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Food Sources of Vitamin E

• Vitamin E is widespread in plant-based foods
• Vegetable oils (safflower, sunflower, canola,
soybean), mayonnaise, salad dressing
• Nuts, seeds, soybeans, avocado
• Vitamin E is destroyed by exposure to
oxygen, metals, ultraviolet light, and heat
• Heating oils destroys vitamin E, fried,
processed, and fast foods contain little
vitamin E

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© 2017 Pearson Education, Inc.


Vitamin E Toxicity
• High supplemental doses of vitamin E may be
harmful for certain individuals with vascular
disease
• Side effects: nausea, intestinal distress, and
diarrhea
• Interacts with anticoagulants (aspirin, Coumadin)
• Long-term use may cause hemorrhagic stroke

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Vitamin E Deficiency
• Deficiency is uncommon in humans, since

vitamin E is stored in fatty tissues
• Associated with fat malabsorption
• Symptom of deficiency: Erythrocyte hemolysis
(rupturing of red blood cells) leads to anemia
• Symptoms: loss of muscle coordination and
reflexes; impaired vision, speech
• Impaired immunity (with low selenium)

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Vitamin C and Its Functions
• Water soluble
• Two active forms: ascorbic acid and
dehydroascorbic acid
• Functions—synthesis of:
• Collagen (prevents scurvy)
• DNA
• Bile
• Neurotransmitters (serotonin)
• Carnitine (transports long-chain fatty acids)
• Hormones (thyroxine, epinephrine, steroids)
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