Transcript 10A. In-Depth: Phytochemicals

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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© 2017 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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© 2017 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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© 2017 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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Antioxidant Minerals Systems: Selenium
• Trace mineral needed in small amounts
• Majority contained in amino acid derivatives:
• Selenomethionine: storage form
• Selenocysteine: active form, part of
glutathione peroxidase enzyme system
• Spares vitamin E
• Needed for thyroxine (thyroid hormone)
production: basal metabolism, body temperature
• Poor status associated with cancer
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© 2017 Pearson Education, Inc.
Selenium Requirements
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Trace amounts to maintain health
RDA: 55 µg/day
UL: 400 µg/day
Sources: organ meats, pork, seafood
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© 2017 Pearson Education, Inc.
Selenium Requirements
• 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 (impaired
immunity to fight disease-causing virus)
• Kashin-Beck disease, deforming arthritis
• Infertility, depression, impaired cognitive
function, muscle pain and wasting
• Cretinism (with iodine deficiency)
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• Kashin-Beck disease creates deforming arthritis.
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Other Minerals Assist in Antioxidant
Function
• Copper, zinc, and manganese are part of the
superoxide dismutase enzyme antioxidant
complex
• Iron is part of the catalase structure
• Manganese: important cofactor in macronutrient
metabolism
• Copper, iron, and zinc for blood health
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Beta-Carotene
• Phytochemical classified as a carotenoid
• Provitamin, inactive form that cannot be used
until converted to active form (precursor of
retinol)
• 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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© 2017 Pearson Education, Inc.
Functions of Beta-Carotene
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Weak antioxidant compared to Vitamin E
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
• Diet rich in carotenoids associated with
decreased cancer risk
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Beta-Carotene Requirements
• Beta-carotene is not an essential nutrient, no
RDA established
• Food sources: red, orange, yellow, and deepgreen fruits and vegetables
• Better absorbed from cooked foods
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© 2017 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
Retinol-binding protein transports retinol
Expressed as Retinol Activity Equivalents (RAE)
International Units (IU) for vitamin A on food
labels or dietary supplements
© 2017 Pearson Education, Inc.
© 2017 Pearson Education, Inc.
© 2017 Pearson Education, Inc.
Vitamin A
• Essential for healthy vision
• Cell differentiation, process by which stem
cells mature into specialized cells
• Differentiates immune cells (T cells) to assist in
fighting infection
• Sperm production and fertilization
• Healthy bone growth
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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 betacarotene can be converted to vitamin A)
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© 2017 Pearson Education, Inc.
Vitamin A Toxicity
• Can be 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 less common in developed countries,
is a severe public health concern in developing
countries
• Deficiency can result in:
• Night blindness
• Xerophthalmia: blindness due to cornea
hardening
• Hyperkeratosis: excess keratin in hair
follicles
• Impaired immunity, failure of normal growth
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© 2017 Pearson Education, Inc.
Disorders Related to Free-Radicals: Cancer
• Cancer: a group of diseases characterized by
cells growing "out of control"
• Cancer cells aggressively invade tissues and
organs throughout the body
• Tumors: immature undifferentiated cell masses
that have no physiologic function
• Malignant (cancerous)
• Benign (harmless)
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Disorders Related to Free-Radicals: Cancer
• Primary steps of cancer development:
• Initiation
• Promotion
• Progression
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© 2017 Pearson Education, Inc.
Cancer
• Risk factors
• Tobacco use
• Overweight, obesity
• Poor nutrition (diets high in saturated fats; low
in fruits & vegetables; excessive alcohol
consumption)
• Physical inactivity
• Infectious agents
• Ultraviolet radiation
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© 2017 Pearson Education, Inc.
• Human papillomavirus (HPV).
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• A malignant melanoma lesion.
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Cancer Prevention
• Antioxidants play a role in cancer prevention
• Enhance immune system
• Inhibit cancer cell growth
• Prevent oxidative damage to cells
• Eat a varied, healthful diet
• Be physically active
• Maintain a healthy body weight
• Quit smoking or don't start
• Avoid infectious agents and UV radiation
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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
• May be even more important than elevated
cholesterol levels
• Weakens plaque in blood vessels (vessels
become more fragile)
• Plaques 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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