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Chapter 10 Lecture Chapter 10: Nutrients Involved in Antioxidant Function and Vision © 2017 Pearson Education, Inc. 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 © 2017 Pearson Education, Inc. 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. © 2017 Pearson Education, Inc. © 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 © 2017 Pearson Education, Inc. © 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 © 2017 Pearson Education, Inc. 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 © 2017 Pearson Education, Inc. © 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 © 2017 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 • Phytochemicals help stabilize free radicals and prevent damage to cells and tissues © 2017 Pearson Education, Inc. 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 © 2017 Pearson Education, Inc. 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 © 2017 Pearson Education, Inc. 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 © 2017 Pearson Education, Inc. © 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 © 2017 Pearson Education, Inc. 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) © 2017 Pearson Education, Inc. © 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 © 2017 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 © 2017 Pearson Education, Inc. 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 © 2017 Pearson Education, Inc. © 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 © 2017 Pearson Education, Inc. 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) © 2017 Pearson Education, Inc. 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) © 2017 Pearson Education, Inc. © 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 © 2017 Pearson Education, Inc. © 2017 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 © 2017 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 © 2017 Pearson Education, Inc. © 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) © 2017 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 © 2017 Pearson Education, Inc. 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 © 2017 Pearson Education, Inc. © 2017 Pearson Education, Inc. Selenium Requirements • • • • Trace amounts to maintain health RDA: 55 µg/day UL: 400 µg/day Sources: organ meats, pork, seafood © 2017 Pearson Education, Inc. © 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) © 2017 Pearson Education, Inc. • Kashin-Beck disease creates deforming arthritis. © 2017 Pearson Education, Inc. 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 © 2017 Pearson Education, Inc. 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 © 2017 Pearson Education, Inc. © 2017 Pearson Education, Inc. Functions of Beta-Carotene • • • • • 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 © 2017 Pearson Education, Inc. 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 © 2017 Pearson Education, Inc. © 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 © 2017 Pearson Education, Inc. Vitamin A • • • • • • 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 © 2017 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 betacarotene can be converted to vitamin A) © 2017 Pearson Education, Inc. © 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 © 2017 Pearson Education, Inc. 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 © 2017 Pearson Education, Inc. © 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) © 2017 Pearson Education, Inc. Disorders Related to Free-Radicals: Cancer • Primary steps of cancer development: • Initiation • Promotion • Progression © 2017 Pearson Education, Inc. © 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 © 2017 Pearson Education, Inc. © 2017 Pearson Education, Inc. • Human papillomavirus (HPV). © 2017 Pearson Education, Inc. • A malignant melanoma lesion. © 2017 Pearson Education, Inc. 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 © 2017 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 © 2017 Pearson Education, Inc. Major Risk Factors for CVD • • • • • Smoking Hypertension High blood levels of LDL cholesterol Obesity Sedentary lifestyle © 2017 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 © 2017 Pearson Education, Inc. 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 © 2017 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 © 2017 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 © 2017 Pearson Education, Inc.