Download Chapter 10

10
Nutrients Involved
in Antioxidant
Function
© 2011 Pearson Education, Inc.
What Are Antioxidants?
• Compounds that protect cells from the
damage caused by oxidation
• Nutrients with antioxidant properties:
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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 a
electron
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© 2011 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
Free Radical Formation
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What Causes Free Radicals?
• Metabolic processes
• Immune system fighting infections
• Environmental factors
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Pollution
Excess sunlight
Toxic substances
Radiation
Tobacco smoke
Asbestos
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Cell Damage
• Free radicals form within the phospholipid
bilayers of cell membranes and steal
electrons
• Damaged lipid molecules cause cell membrane to
lose its integrity
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© 2011 Pearson Education, Inc.
Diseases Linked with Free Radicals
• Free radicals damage low-density lipoproteins
(LDLs), cell proteins, and DNA
• Increase risk for chronic diseases
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Heart disease
Various cancers
Diabetes
Cataracts
Alzheimer’s disease
Parkinson’s disease
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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
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Antioxidant Enzymes
• Antioxidant enzyme systems
• Break down oxidized fatty acids
• Make more vitamin antioxidants available to fight
other free radicals
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Antioxidant Enzymes
• 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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Antioxidants
• Other compounds stabilize free radicals and
prevent damage to cells and tissues
• Nutrients with antioxidant properties:
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Vitamin E
Vitamin C
Vitamin A
Beta-carotene (precursor to vitamin A)
Selenium
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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)
• Stored in adipose tissue, cell membranes
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Forms of Vitamin E
• 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 or International
Units (IU)
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Functions of Vitamin E
• Protects polyunsaturated fatty acids (PUFAs),
fatty cell components, and LDLs from
oxidization (lower heart disease risk)
• Added to oil-based foods and skincare
products to reduce rancidity and spoilage
• Normal nerve and muscle development
• Enhances immune system
• Promotes vitamin A absorption, if 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 foods
• Vegetable oils (safflower, sunflower, canola,
soybean), mayonnaise, salad dressing
• Nuts, seeds, soybeans
• Wheat germ, fortified cereals
• Vitamin E is destroyed by exposure to oxygen,
metals, ultraviolet light, and heat
• Little vitamin E in deep-fried, processed foods
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© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Vitamin E toxicity
• High supplemental doses of vitamin E may be
harmful for certain individuals
• 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 rare
• Erythrocyte hemolysis (rupturing of red blood
cells) leads to anemia
• Anemia in premature infants
• Symptoms: loss of muscle coordination and
reflexes; impaired vision, speech
• Impaired immunity (with low selenium)
• Associated with fat malabsorption
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Vitamin C and Its Functions
• Water soluble
• Functions—synthesis of:
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Collagen (prevents scurvy)
DNA
Bile
Neurotransmitters (serotonin)
Carnitine (transports long-chain fatty acids)
Hormones (thyroxine, epinephrine, steroids)
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© 2011 Pearson Education, Inc.
More Functions of Vitamin C
• Antioxidant for protecting:
• LDL-cholesterol from oxidation
• Lungs from ozone and cigarette damage
• White blood cells (enhances immune function)
• Reduces nitrosamines, cancer-causing agent
found in cured and processed meats
• Regenerates oxidized vitamin E
• Enhances iron absorption
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© 2011 Pearson Education, Inc.
Vitamin C Requirements
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RDA: 90 mg/day (men), 75 mg/day (women)
UL: 2,000 mg/day for adults
Smokers require additional 35 mg/day
Other situations requiring more vitamin C:
• Healing from traumatic injury, surgery, burns
• Use of oral contraceptives
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Food Sources of Vitamin C
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Best sources: fresh fruits and vegetables
Destroyed by heat and oxygen
Can be leached into boiling water
Minimize loss: steaming, microwaving, and
stir-frying
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© 2011 Pearson Education, Inc.
Too Much Vitamin C?
• Water soluble
• Extra excreted; consuming excess is not toxic
• Only supplements can lead to toxic doses
• Megadoses
• Long-term excess of 2,000 mg/day: nausea,
diarrhea, nosebleeds, and abdominal cramps
• Harmful for people with hemochromatosis (excess
iron accumulation in the body)
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Not Enough Vitamin C?
• Rare in developed countries
• Scurvy: most common deficiency disease
• Symptoms: bleeding gums, loose teeth,
weakness, wounds that fail to heal, bone pain
and fractures, diarrhea, depression
• Anemia can result
• High risk for deficiency among people with
• Low fruit and vegetable intake
• Alcohol and drug abuse
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Beta-Carotene
• Provitamin A, inactive form (precursor) of
vitamin A to be converted to active retinol
• Phytochemical classified as a carotenoid
• Expressed in food as Retinol Activity
Equivalents (RAE), which indicates how much
active vitamin A is available to the body after
conversion
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© 2011 Pearson Education, Inc.
Functions of Beta-Carotene
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Weak antioxidant
Fights lipid oxidation in cell membranes
Enhances immune system
Protects skin from UV-ray damage
Protects eyes from damage, preventing or
delaying age-related vision impairment
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Beta-Carotene Requirements
• Beta-carotene is not an essential nutrient
• No RDA established
• Consuming 6 to 10 mg of beta-carotene per
day from food sources may reduce the risks
for cancer and heart disease
• Food sources: red, orange, yellow, and deepgreen fruits and vegetables
• Heat improves digestibility and absorption
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© 2011 Pearson Education, Inc.
Beta-Carotene Requirements
• Large consumption is not toxic
• Carotenosis (carotenodermia): reversible and
harmless
• Supplementation is not recommended; adequate
amounts from fruits and vegetables
• Not enough?
• No known deficiency symptoms
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Vitamin A
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Fat soluble
Active forms: retinol, retinal, retinoic acid
Stored mainly in the liver
Expressed as Retinol Activity Equivalents
(RAE)
• International Units (IU) for vitamin A on food
labels or dietary supplements
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© 2011 Pearson Education, Inc.
Functions of Vitamin A
• Antioxidant, scavenges free radicals and
protects LDL from oxidation
• Essential for healthy vision
• Cell differentiation, process by which stem
cells mature into specialized cells
• Sperm production and fertilization
• Bone growth
Vitamin A and Epithelial
Tissue
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© 2011 Pearson Education, Inc.
Vitamin A Requirements
• RDA is 900 micrograms/day for men, 700
micrograms/day for women
• UL: 3,000 micrograms/day preformed
vitamin A
• Food sources
• Animal (liver, eggs, dairy, fortified foods)
• Plants (dark-green, orange, and deep-yellow fruits
and vegetables that are high in beta-carotene can
be converted to vitamin A)
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© 2011 Pearson Education, Inc.
Vitamin A Requirements
• Highly toxic, mainly from supplements
• Birth defects, spontaneous abortion
• Symptoms: fatigue, loss of appetite, blurred
vision, hair loss, skin disorders, bone and joint
pain, abdominal pain, nausea, diarrhea, and
damage to the liver and nervous system
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Vitamin A Requirements
• Deficiency
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Night blindness
Xerophthalmia
Hyperkeratosis
Impaired immunity, failure of normal growth
Vitamin A and the Visual
Cycle
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© 2011 Pearson Education, Inc.
Selenium
• Trace mineral needed in small amounts
• Antioxidant (part of glutathione peroxidase
enzyme system): spares vitamin E
• Thyroxine (thyroid hormone) production:
basal metabolism, body temperature
• RDA: 55 µg/day; UL: 400 µg/day
• Sources: organ meats, pork, seafood
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© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Selenium
• Toxicity can occur from supplements
• Brittle hair and nails, skin rashes, vomiting,
nausea, weakness, cirrhosis of the liver
• Deficiency associated with
• Keshan disease, a heart disease
• Kashin-Beck disease, deforming arthritis
• Impaired immunity
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© 2011 Pearson Education, Inc.
Additional Antioxidants
• Copper, zinc, and manganese are part of the
superoxide dismutase enzyme antioxidant
complex
• Iron is part of the catalase structure
• Copper, iron, and zinc for blood health
• Manganese: important cofactor in
carbohydrate metabolism
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Cancer
• A group of diseases characterized by cells
growing “out of control”
• Tumors: immature undifferentiated cell
masses that have no physiologic function
• Malignant (cancerous); benign (harmless)
• Primary steps of cancer development:
• Initiation
• Promotion
• Progression
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© 2011 Pearson Education, Inc.
Cancer Risk
• Risk factors
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Tobacco use
Unhealthful diet
Infectious agents
Ultraviolet radiation
Physical inactivity
ABC Video Tobacco Addiction
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© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Cancer Risk
• Antioxidants prevent cancer
• Enhance immune system
• Inhibit cancer cell growth
• Prevent oxidative damage to cells
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Cardiovascular Disease (CVD)
• Leading cause of death in adults (U.S.)
• Diseases of the heart and blood vessels
• Coronary heart disease
• Hypertension (high blood pressure)
• Atherosclerosis (hardening of the arteries)
• Primary manifestations of CVD
• Heart attack
• Stroke
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Major Risk Factors for CVD
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Smoking
Hypertension
High blood levels of LDL cholesterol
Obesity
Sedentary lifestyle
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Other Risk Factors for CVD
• Low blood levels of HDL cholesterol
• Diabetes
• Family history of CVD
• Males before age 55
• Females before age 65
• Being male older than 45 years
• Being postmenopausal woman
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Low-Grade Inflammation
• More important than elevated cholesterol?
• Weakens plaque in blood vessels (more
fragile)
• Likely to burst, break away, lodge in blood vessels
of heart or brain, and close off blood supply,
resulting in a heart attack or stroke
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Low-Grade Inflammation
• C-reactive protein (CRP)
• Marker for inflammation (blood test)
• Associated with high risk for heart attack in the
presence of normal cholesterol levels
• High CRP and high cholesterol can increase the
risk for heart attack
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Antioxidants and CVD
• Antioxidants (vitamins E and lycopene)
reduce damage to blood vessels:
• Scavenge free radicals
• Reduce low-grade inflammation
• Reduce blood coagulation and clot formation
• In fruits, vegetables, and whole grains
• Dietary fiber (soluble):oatmeal and oat bran
• Folate (reduce homocysteine-CVD risk factor)
• Others (flavonoids): tea
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Age-Related Vision Impairment
• Macular degeneration
• Leading cause of blindness
• Deterioration of center portion of retina
• Loss of the ability to see details
• Cataract
• Damaged portion of eye’s lens (cloudy vision)
• Impaired adjustment from dark to bright light
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© 2011 Pearson Education, Inc.
Age-Related Vision Impairment
• Possible role of antioxidants
• Supplements may reduce progression of macular
degeneration
• Mixed results from cataract research
• Current research does not support the use of
antioxidant supplements to prevent these two
diseases of aging
© 2011 Pearson Education, Inc.