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Lecture Outline Chapter 8 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Vitamins Chapter 8 Insert photo from 1 st page of chapter
Chapter Learning Outcomes 1.Classify vitamins according to whether they are fat- soluble or water-soluble. 2.List major functions and sources for each vitamin. 3.Describe deficiency and/or toxicity signs and symptoms for certain vitamins, including A, D, thiamin, folate, and C. 4.Discuss ways to conserve the vitamin content of foods. 5.Evaluate the use of vitamin supplements with respect to their potential health benefits and hazards.
Quiz Yourself True or False Quiz Yourself True or False 1.Natural vitamins are better for you because they have more biological activity than synthetic vitamins. T F 2.Certain vitamins are toxic. T F 3.Vitamin E is an antioxidant. T F 4.Vitamins are a source of “quick” energy. 5.According to scientific research, taking large doses of vitamin C daily prevents the common cold. T F
How Did You Do? How Did You Do? 1.False In most instances, natural vitamins have the same activity in the body as synthetic vitamins. 2.True Certain vitamins are toxic. 3.True Vitamin E is an antioxidant. 4.False Vitamins are not a source of kilocalories. 5.False According to results of most scientific research, megadoses of vitamin C do not prevent the common cold.
Vitamins: Basic Concepts What is a vitamin? A complex organic compound that: –The body can’t make — or make enough to maintain good health –Naturally occurs in common foods –Deficiency condition occurs when the vitamin is missing in the diet –Good health is restored, if deficiency disorder is treated early
Vitamins: Basic Concepts Most vitamins have more than 1 formMost vitamins have more than 1 form –Vitamin A = retinol, retinal, retinoic acid Provitamins are vitamin precursors that do not function in the body until converted to active forms.Provitamins are vitamin precursors that do not function in the body until converted to active forms. –Beta-carotene (plant pigment) = precursor to vitamin A –Tryptophan = (amino acid) precursor to B-vitamin niacin
How Vitamins Differ from Carbohydrate, Fat, and Protein Vitamins Organic Organic No Calories Micronutrients Micronutrients Foods contain very small amounts (milligrams or micrograms) Carbs, Fats, Proteins Organic Provides Calories Macronutrients Foods contain relatively large amounts (grams) Same Differ
Vitamins Are Micronutrients Comparing Amounts of Nutrients in a Food A slice of bread weighs about 1 oz (28 g)A slice of bread weighs about 1 oz (28 g) Vitamins comprise only ~0.005% (1.48 mg) of the bread’s weightVitamins comprise only ~0.005% (1.48 mg) of the bread’s weight Insert slice of bread from page 224
Roles of Vitamins Vitamins may: hormonal action – Have hormonal action (e.g., vitamin D) Participate – Participate in certain chemical reactions Regulate – Regulate certain body processes – Cell division and development – Growth and maintenance of tissues
Vitamins and Their Functions Insert figure 8.1
Do Vitamins Supply Any Calories? Vitamins do not supply energy, but many participate in the chemical reactions that release the energy stored in macronutrients.
Oxidation = loss of electronsOxidation = loss of electrons Reduction = gain of electronsReduction = gain of electrons Oxidation reactions can form radicals (or “free radicals”), substances with unpaired electrons.Oxidation reactions can form radicals (or “free radicals”), substances with unpaired electrons. Antioxidants are substances that give up electrons to stabilize free radicals.Antioxidants are substances that give up electrons to stabilize free radicals. What is an Antioxidant?
Most free radicals are highly reactive substancesMost free radicals are highly reactive substances –they have an unpaired electron A free radical can remove an electron from a more stable molecule, such as DNA, a protein, or a polyunsaturated fatty acid.A free radical can remove an electron from a more stable molecule, such as DNA, a protein, or a polyunsaturated fatty acid. Free Radical Insert Figure 8.2
How Do Antioxidants Work? giving upBy giving up an electron to a free radical, an antioxidant protects other molecules. – Action stabilizes the free radical Beta-carotenevitamins ECBeta-carotene and vitamins E and C function as antioxidants.
Classifying Vitamins Fat-soluble A, D, E,K Fat-soluble — A, D, E, and K - Associated with lipids in foods and the body - Don’t dissolve in water or urine - Stored in the body and may be toxic Water-soluble B Ccholine Water-soluble — B vitamins, C, and choline - Dissolve in watery components of foods and the body - Excreted in urine - Most are not stored to a major extent - Generally non toxic
Fat -Soluble Vitamins Insert Table 8.1
Water- soluble Vitamins Insert Table 8.1
Sources of Vitamins Natural Sources Natural Sources: Plants, animals, fungi, and bacteria Synthetic Synthetic: Made in laboratories by chemists Synthesized by microbes in laboratories and extracted for commercial use Most natural and synthetic forms have equal activity in the body except: Natural vitamin E Natural vitamin E: greater biological activity than synthetic Synthetic folate Synthetic folate: greater biological activity than natural
Vitamin Enrichment and Fortification Vitamin Enrichment and Fortification EnrichmentEnrichment –Addition of specific amounts of thiamin, riboflavin, niacin, folic acid, and the mineral iron to refined flour and milled grains Grains lose considerable amounts of their natural vitamin/mineral contents during refinement FortificationFortification –Addition of one or more nutrients to a wide array of commonly eaten processed foods during their manufacturing
Vitamin Absorption Vitamin Absorption Most absorption occurs in small intestine – Absorption is not 100% efficient. Absorption generally increases when more of the vitamin is needed: –Growth (e.g., during infancy and adolescence) –Pregnancy –Lactation (milk production)
Vitamin Absorption Vitamin Absorption Fat soluble are absorbed with dietary fat – Some fat is needed in the diet. Diseases that affect the GI tract can reduce vitamin absorption. –Cystic fibrosis –Cystic fibrosis (CF) interferes with fat digestion and fat-soluble vitamin absorption People with CF and other intestinal diseases may need to take supplemental sources of vitamins.
Vitamin Deficiency and Toxicity Disorders Vitamin Deficiency and Toxicity Disorders Deficiencies result from poor diets or certain health conditions. –In the United States, severe deficiencies are uncommon because of: Food preservation practices Food enrichment and fortification Widespread availability of fruits and vegetables 25 AEC.According to dietary surveys: at least 25% of Americans consume inadequate amounts of A, E, and C.
Populations at Risk for Vitamin Deficiency (U.S.) Populations at Risk for Vitamin Deficiency (U.S.) AlcoholicsAlcoholics ElderlyElderly Hospitalized (long-term)Hospitalized (long-term) Anorexia nervosaAnorexia nervosa Certain gastrointestinal disordersCertain gastrointestinal disorders Rare metabolic conditionsRare metabolic conditions
Preserving Vitamin Content of Foods Preserving Vitamin Content of Foods Are fresh fruits and vegetables better sources of vitamins than canned or frozen product? It depends… Two main factors that influence vitamin retention in product are: Two main factors that influence vitamin retention in product are: 1) Length of time since harvest 2) Storage conditions since harvest 2) Storage conditions since harvest
Which Vitamins are Susceptible to Loss? Vitamin C, thiamin, and folate are easily destroyed by improper storage and preparation practices.Vitamin C, thiamin, and folate are easily destroyed by improper storage and preparation practices. Niacin and vitamin D tend to be very stable.Niacin and vitamin D tend to be very stable.
Ways to Maximize Vitamin Contents of Foods Avoid buying wilted, bruised, or shriveled produce.Avoid buying wilted, bruised, or shriveled produce. Store at near freezing temperatures, in high humidity and air-tight containers.Store at near freezing temperatures, in high humidity and air-tight containers. Cook in small amounts of water.Cook in small amounts of water. Avoid cutting foods that will be cooked into small pieces.Avoid cutting foods that will be cooked into small pieces. Use quick cooking methods such as microwaving, steaming, and stir-frying.Use quick cooking methods such as microwaving, steaming, and stir-frying. Freeze produce to preserve vitamins.Freeze produce to preserve vitamins.
Vitamin A Vitamin A Retinolpreformed A Retinol (preformed A) Most active form of the vitamin In animal foods Beta-caroteneprovitamin A Beta-carotene (provitamin A) carotenoids One of a few carotenoids (plant pigments) that the body can convert to retinol Major functions –Normal vision and reproduction –Cellular growth –Immune system function –Epithelial cell production and maintenance
Vitamin A Vitamin A What is night blindness?What is night blindness? –The inability to see in dim light –An early sign of vitamin A deficiency The retina, the light- sensitive area inside each eye, contains rods and cones, specialized nerve cells essential for vision.The retina, the light- sensitive area inside each eye, contains rods and cones, specialized nerve cells essential for vision. Rods and cones need vitamin A to function properly.Rods and cones need vitamin A to function properly.
Insert Figure 8.7Insert Figure 8.7 Vitamin A and Vision
Insert Table 8.3Insert Table 8.3 Vitamin A Content of Selected Foods
Vitamin A Vitamin A Dietary AdequacyDietary Adequacy –RDA: mcg RAE Vitamin A DeficiencyVitamin A Deficiency –Certain epithelial cells produce too much keratin Keratin - tough protein found in hair, nails, and outermost layers of skinKeratin - tough protein found in hair, nails, and outermost layers of skin –Excess keratin: Skin becomes rough and bumpySkin becomes rough and bumpy Inner eyelid cells that secrete mucus to protect cornea become keratinized.Inner eyelid cells that secrete mucus to protect cornea become keratinized. – Can result in xeropthalmia “dry eye”
Xerophthalmia If u ntreated, vitamin A deficiency eventually leads to blindness.
What is Carotenemia? Carotenemia –Yellowing of skin due to excessive beta-carotene intake May occur in infants who eat too much orange/yellow or dark green baby foods: carrots, apricots, winter squash, sweet potatoes, peas, green beans, etc.May occur in infants who eat too much orange/yellow or dark green baby foods: carrots, apricots, winter squash, sweet potatoes, peas, green beans, etc. –Typically harmless
Vitamin D Vitamin D Rickets: vitamin D deficiency in children - Results in soft bones that do not grow properly and become misshapen
Insert Figure 8.10Insert Figure 8.10 Vitamin D: The “Sunshine Vitamin” Synthesis and Functions
Why Is Vitamin D Necessary? Why Is Vitamin D Necessary? Vitamin D is needed for : –Metabolism of calcium and phosphorus –Production and maintenance of healthy bones Parathyroid hormone (PTH) –Released when blood calcium levels drop –Stimulates kidneys to increase active vitamin D production and decrease urinary calcium excretion
People who live south of the 37 th parallel and are outdoors when sunlight is most intense are most likely synthesizing adequate previtamin D. Vitamin D and Sunlight Insert Figure 8.12
Dietary AdequacyDietary Adequacy –AI: 5 mcg/day (200 IU) for people < 50 years of age Vitamin D DeficiencyVitamin D Deficiency – Rickets Rare in the U.S. because many foods are fortified with vitamin DRare in the U.S. because many foods are fortified with vitamin D May develop in breastfed infantsMay develop in breastfed infants – Osteomalacia -- “adult rickets” Vitamin D Adequacy and Deficiency
Upper Limit (UL)Upper Limit (UL) – 50 mcg/day (2000 IU) Vitamin D toxicityVitamin D toxicity –Too much calcium is absorbed The excess calcium is deposited in soft tissues including kidneys, heart, and blood vessels. The excess calcium is deposited in soft tissues including kidneys, heart, and blood vessels. Vitamin D Toxicity
Alpha-tocopherol Functions:Functions: –Major fat-soluble antioxidant found in cell Protects polyunsaturated fatty acidsProtects polyunsaturated fatty acids –Improves vitamin A absorption –Maintains nervous system and immune system function Vitamin E
Insert Table 8.5Insert Table 8.5 Selected Food Sources of Vitamin E
Dietary AdequacyDietary Adequacy –RDA: 15 mg/day Vitamin E DeficiencyVitamin E Deficiency –Hemolysis (breaking apart) of RBC Due to oxidation of polyunsaturated fatty acids in cell membraneDue to oxidation of polyunsaturated fatty acids in cell membrane Vitamin E ToxicityVitamin E Toxicity –Upper Limit (UL) 1000 mg/day –Excess may interfere with vitamin K’s role in blood clotting Vitamin E Adequacy, Deficiency, and Toxicity
Water-Soluble Vitamins Most function as components of specific coenzymes Coenzymes: small molecules that regulate chemical reactions by interacting with enzymesCoenzymes: small molecules that regulate chemical reactions by interacting with enzymes Ins ert Fig ure Coenzymes are comprised of B vitamin and a nitrogen- containing substance
Coenzyme Function Once activated, the enzyme-coenzyme complex enables the reaction to occur. Insert figure 8.16
Insert Figure 8.17Insert Figure 8.17 MyPyramid and the Water-Soluble Vitamins
FunctionsFunctions – Part of coenzyme involved in release of energy from carbohydrates – Metabolism of certain amino acids – Synthesis of neurotransmitters Dietary AdequacyDietary Adequacy –RDA = 1.2 mg/day (men) 1.2 mg/day (women) DeficiencyDeficiency –Not stored deficiency symptoms can occur within in a few daysdeficiency symptoms can occur within in a few daysThiamin
Beriberi Thiamin deficiencyThiamin deficiency condition condition People are weak, have poor muscular coordination, and may develop cardiovascular problems and edema.People are weak, have poor muscular coordination, and may develop cardiovascular problems and edema. Insert figure 8.18
FunctionsFunctions –Coenzyme for metabolism of carbohydrate, lipids, and amino acids Dietary AdequacyDietary Adequacy –RDA = 1.3 mg/day (males) 1.1 mg/day (females) DeficiencyDeficiency –May occur in people who do not drink milk or eat enriched grains Riboflavin
FunctionsFunctions – Part of two coenzymes that participate in at least 200 reactions Dietary AdequacyDietary Adequacy – RDA = mg/day DeficiencyDeficiency – Pellagra—the “4 D’s” of pellagra Dermatitis, Diarrhea, Dementia, Death Niacin
Insert Table 8.9 Selected Food Sources of Niacin
FunctionsFunctions –Part of coenzyme needed for amino acid metabolism Dietary AdequacyDietary Adequacy –RDA = 1.3 to 1.7 mg/day DeficiencyDeficiency –Rarely occurs, but signs and symptoms include: Dermatitis, anemia, convulsions, depression, and confusionDermatitis, anemia, convulsions, depression, and confusion Vitamin B-6
Insert Table 8.10 Selected Food Sources of B-6
Folic Acid (synthetic) and FolacinFolic Acid (synthetic) and Folacin FunctionsFunctions –Part of coenzyme tetrahydrofolic acid (THFA) THFA involved in DNA and amino acid metabolismTHFA involved in DNA and amino acid metabolism Conversion of homocysteine to methionineConversion of homocysteine to methionine Good Food Sources of FolateGood Food Sources of Folate –Leafy green vegetables, liver, legumes, asparagus, broccoli, and oranges Dietary AdequacyDietary Adequacy –RDA = 400 mcg DFE/day Folate
DeficiencyDeficiency –Affects cells that rapidly divide, such as RBCs Mature RBCs do not have nuclei and live ~ 4 monthsMature RBCs do not have nuclei and live ~ 4 months – without folate, RBC precursor cells enlarge, but cannot divide (DNA is needed for division) Bone marrow releases some large, immature,Bone marrow releases some large, immature, abnormal RBCs with nuclei (megaloblasts) into the blood stream. Folate
Insert Figure 8.20Insert Figure 8.20 Red Blood Cell (RBC) Production
During the first few weeks after conception, the neural tube forms.During the first few weeks after conception, the neural tube forms. –Neural tube develops into the brain and spinal cord. Folate-deficient pregnant women are at risk of giving birth to infants with neural tube defects.Folate-deficient pregnant women are at risk of giving birth to infants with neural tube defects. Neural Tube Defects
Two Common Types of Neural Tube Defects Two Common Types of Neural Tube Defects Spina bifidaSpina bifida –Spinal bones do not form properly before birth and fail to enclose the spinal cord. AnencephalyAnencephaly –Brain does not form properly or is missing. Neural Tube Defects
FunctionsFunctions – Part of coenzymes needed for: Folate metabolismFolate metabolism Maintenance of myelin sheathsMaintenance of myelin sheaths Absorption of Dietary B-12Absorption of Dietary B-12 – B-12 in food is bound to proteins HCL and pepsin required to release B-12 from proteinsHCL and pepsin required to release B-12 from proteins – B-12 must bind to intrinsic factor for absorption. Vitamin B-12
Dietary AdequacyDietary Adequacy –RDA = 2.4 mcg/day DeficiencyDeficiency –Pernicious Anemia Genetic defect reduces production of intrinsic factor and results in poor B-12 absorption.Genetic defect reduces production of intrinsic factor and results in poor B-12 absorption. Signs and symptoms:Signs and symptoms: –megaloblastic anemia, nerve damage, weakness, sore tongue, memory loss, confusion, difficulty walking and maintaining balance, and eventual death Vitamin B-12
Functions — not part of a coenzymeFunctions — not part of a coenzyme – Collagen synthesis protein that gives strength to connective tissuesprotein that gives strength to connective tissues – Antioxidant activity – Other Roles: Immune system functioningImmune system functioning Synthesis of bile, and certain neurotransmitters and hormonesSynthesis of bile, and certain neurotransmitters and hormones Dietary AdequacyDietary Adequacy –RDA = 75 to 90 mg/day (smokers have higher RDAs) Vitamin C
Insert Table 8.13Insert Table 8.13 Selected Food Sources of Vitamin C
Toxicity UL is 2000 mg/dayUL is 2000 mg/day Kidneys excrete excess amounts of the vitamin and oxalate, a byproduct of vitamin C metabolismKidneys excrete excess amounts of the vitamin and oxalate, a byproduct of vitamin C metabolism –Increases risk of oxalate kidney stones, particularly in susceptible persons Deficiency ScurvyScurvy –Very rare in U.S., because about 10 mg/day prevents scurvy –Signs and symptoms: poor wound healing, pinpoint hemorrhages, bleeding gums, bruises, and depression Vitamin C
Chapter 8 Highlight Megadosing on Vitamins Niacin As Medicine? UsesUses –Given to lower LDL cholesterol and raise HDL cholesterol Side effectsSide effects –Flushing of skin on face and chest, itchy skin, GI tract upset, and liver damage
Vitamin B-6 As Medicine? UsesUses –Claims include help for symptoms of PMS and carpal tunnel syndrome. –Weak or no scientific support for claims Side effects of high dosesSide effects of high doses –Severe sensory nerve damage –Walking difficulties –Numbness of hands and feet Because of side effects, not recommended for treating PMSBecause of side effects, not recommended for treating PMS
Folic Acid As Medicine? UseUse –Lowers blood homocysteine levels when taken with B-12 and B-6 CVDCVD –Recent studies of subjects with CVD suggest folic acid supplements do not reduce risk of having heart another heart attack. Alzheimer’s diseaseAlzheimer’s disease »May be a relationship between mild cognitive impairment and folate deficiency or elevated blood homocysteine »More research is needed to determine whether taking supplements to lower homocysteine can reduce risk of cognitive decline or slow progression of Alzheimer’s.
Vitamin C As Medicine? UsesUses – Does not prevent common cold but may reduce severity of the infection –Reduces oxidation of LDL cholesterol More research is needed to determine whether high doses help reduce CVD riskMore research is needed to determine whether high doses help reduce CVD risk –More research is needed to determine whether vitamin C helps reduce cancer risk or aids in cancer treatment
Carotenoids As Medicine? UsesUses –Cancer Older studies suggested diets rich in carotenoids were associated with lower risk of cancers.Older studies suggested diets rich in carotenoids were associated with lower risk of cancers. – Dietary supplements containing beta-carotene failed to show benefit– may be harmful. Diets rich in fruits and vegetables associated with lower CVD riskDiets rich in fruits and vegetables associated with lower CVD risk –Dietary supplements containing beta-carotene and other carotenoids fail to show benefit. –Age-related Macular Degeneration (AMD) Diets that supply high amounts of certain carotenoids may lower risk of AMD.Diets that supply high amounts of certain carotenoids may lower risk of AMD.
Vitamin E As Medicine? Questionable BenefitsQuestionable Benefits –Recent studies did not support taking vitamin E (alpha-tocopherol) supplements to reduce risk of heart attacks, cancer, macular degeneration, and cognitive impairment. –Future studies using other forms of vitamin E may provide scientific support for taking the vitamin to prevent or treat certain diseases.
Some Final Thoughts U.S. Preventive Services Task Force:U.S. Preventive Services Task Force: “Taking vitamins does not replace the need to eat a healthy diet.” Consuming a wide variety of vitamins, antioxidants, and phytochemical in their natural state and concentrations may be the most effective way to lower risk of CVD, cancer, and other serious chronic diseases.Consuming a wide variety of vitamins, antioxidants, and phytochemical in their natural state and concentrations may be the most effective way to lower risk of CVD, cancer, and other serious chronic diseases.