Antioxidant i

© 2011 Pearson Education, Inc.

10Nutrients Involved

in Antioxidant Function


What Are Antioxidants?

• Compounds that protect cells from the damage caused by oxidation

• Nutrients with antioxidant properties:• Vitamin E• Vitamin C• Vitamin A (precursor beta-carotene)• Selenium


Exchange Reactions

• Oxidation is a chemical reaction in which atoms lose electrons

• Reduction occurs when atoms gain a electron



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


What Causes Free Radicals?

• Metabolic processes • Immune system fighting infections

• Environmental factors• Pollution• Excess sunlight• Toxic substances• Radiation• Tobacco smoke• Asbestos


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



Diseases Linked with Free Radicals

• Free radicals damage low-density lipoproteins (LDLs), cell proteins, and DNA

• Increase risk for chronic diseases• Heart disease• Various cancers• Diabetes• Cataracts• Alzheimer’s disease• Parkinson’s disease


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


Antioxidant Enzymes

• Antioxidant enzyme systems• Break down oxidized fatty acids • Make more vitamin antioxidants available to fight

other free radicals


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


Antioxidants

• Other compounds stabilize free radicals and prevent damage to cells and tissues

• Nutrients with antioxidant properties:• Vitamin E• Vitamin C• Vitamin A • Beta-carotene (precursor to vitamin A)• Selenium


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


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)



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


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


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




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


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


Vitamin C and Its Functions

• Water soluble• Functions—synthesis of: • Collagen (prevents scurvy)• DNA• Bile• Neurotransmitters (serotonin)• Carnitine (transports long-chain fatty acids)• Hormones (thyroxine, epinephrine, steroids)



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



Vitamin C Requirements

• 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


Food Sources of Vitamin C

• Best sources: fresh fruits and vegetables• Destroyed by heat and oxygen• Can be leached into boiling water• Minimize loss: steaming, microwaving, and

stir-frying



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)


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


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



Functions of Beta-Carotene

• 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


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 deep-green fruits and vegetables

• Heat improves digestibility and absorption



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


Vitamin A

• 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



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



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)




• 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



• Deficiency • Night blindness• Xerophthalmia• Hyperkeratosis• Impaired immunity, failure of normal growth

Vitamin A and the Visual Cycle



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




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



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


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



Cancer Risk

• Risk factors• Tobacco use• Unhealthful diet• Infectious agents• Ultraviolet radiation• Physical inactivity

ABC Video Tobacco Addiction






Cancer Risk

• Antioxidants prevent cancer• Enhance immune system• Inhibit cancer cell growth• Prevent oxidative damage to cells


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


Major Risk Factors for CVD

• Smoking• Hypertension• High blood levels of LDL cholesterol• Obesity• Sedentary lifestyle


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


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


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


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


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



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

Documents

Antioxidant i