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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: • • • • Vitamin E Vitamin C Vitamin A (precursor beta-carotene) Selenium © 2011 Pearson Education, Inc. Exchange Reactions • Oxidation is a chemical reaction in which atoms lose electrons • Reduction occurs when atoms gain a electron © 2011 Pearson Education, Inc. © 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 © 2011 Pearson Education, Inc. What Causes Free Radicals? • Metabolic processes • Immune system fighting infections • Environmental factors • • • • • • Pollution Excess sunlight Toxic substances Radiation Tobacco smoke Asbestos © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. © 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 • • • • • • Heart disease Various cancers Diabetes Cataracts Alzheimer’s disease Parkinson’s disease © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. Antioxidant Enzymes • Antioxidant enzyme systems • Break down oxidized fatty acids • Make more vitamin antioxidants available to fight other free radicals © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. 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 © 2011 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) • Stored in adipose tissue, cell membranes © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. © 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 © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. 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) © 2011 Pearson Education, Inc. © 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 © 2011 Pearson Education, Inc. © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. © 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) © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. © 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 © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. © 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 © 2011 Pearson Education, Inc. © 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) © 2011 Pearson Education, Inc. © 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 © 2011 Pearson Education, Inc. Vitamin A Requirements • Deficiency • • • • Night blindness Xerophthalmia Hyperkeratosis Impaired immunity, failure of normal growth Vitamin A and the Visual Cycle © 2011 Pearson Education, Inc. © 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 © 2011 Pearson Education, Inc. © 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 © 2011 Pearson Education, Inc. © 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 © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. © 2011 Pearson Education, Inc. Cancer Risk • Risk factors • • • • • Tobacco use Unhealthful diet Infectious agents Ultraviolet radiation Physical inactivity ABC Video Tobacco Addiction © 2011 Pearson Education, Inc. © 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 © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. Major Risk Factors for CVD • • • • • Smoking Hypertension High blood levels of LDL cholesterol Obesity Sedentary lifestyle © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. © 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.