Presentation on theme: "Lecture Outline Chapter 8"— Presentation transcript:
1 Lecture Outline Chapter 8 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
2 Vitamins Chapter 8Insert photo from 1st page of chapter
3 Chapter Learning Outcomes Classify vitamins according to whether they are fat-soluble or water-soluble.List major functions and sources for each vitamin.Describe deficiency and/or toxicity signs and symptoms for certain vitamins, including A, D, thiamin, folate, and C.Discuss ways to conserve the vitamin content of foods.Evaluate the use of vitamin supplements with respect to their potential health benefits and hazards.
4 Quiz Yourself True or False Quiz Yourself True or FalseNatural vitamins are better for you because they have more biological activity than synthetic vitamins. T FCertain vitamins are toxic. T FVitamin E is an antioxidant. T FVitamins are a source of “quick” energy.According to scientific research, taking large doses of vitamin C daily prevents the common cold. T F
5 How Did You Do?False In most instances, natural vitamins have the same activity in the body as synthetic vitamins.True Certain vitamins are toxic.True Vitamin E is an antioxidant.False Vitamins are not a source of kilocalories.False According to results of most scientific research, megadoses of vitamin C do not prevent the common cold.
6 Vitamins: Basic Concepts What is a vitamin?A complex organic compound that:The body can’t make — or make enough to maintain good healthNaturally occurs in common foodsDeficiency condition occurs when the vitamin is missing in the dietGood health is restored, if deficiency disorder is treated early
7 Vitamins: Basic Concepts Most vitamins have more than 1 formVitamin A = retinol, retinal, retinoic acidProvitamins are vitamin precursors that do not function in the body until converted to active forms.Beta-carotene (plant pigment) = precursor to vitamin ATryptophan = (amino acid) precursor to B-vitamin niacin
8 How Vitamins Differ from Carbohydrate, Fat, and Protein OrganicNo CaloriesMicronutrientsFoods contain very small amounts (milligrams or micrograms)Carbs, Fats, ProteinsOrganicProvides CaloriesMacronutrientsFoods contain relatively large amounts(grams)SameDiffer
9 Vitamins Are Micronutrients Comparing Amounts of Nutrients in a FoodA slice of bread weighs about 1 oz (28 g)Vitamins comprise only ~0.005% (1.48 mg) of the bread’s weightInsert slice of bread from page 224
10 Roles of Vitamins Vitamins may: Have hormonal action (e.g., vitamin D) Participate in certain chemical reactionsRegulate certain body processesCell division and developmentGrowth and maintenance of tissues
12 Do Vitamins Supply Any Calories? Vitamins do not supply energy, but manyparticipate in the chemical reactions that release the energy stored in macronutrients.
13 What is an Antioxidant? Oxidation = loss of electrons Reduction = gain of electronsOxidation reactions can form radicals (or “free radicals”), substances with unpaired electrons.Antioxidants are substances that give up electrons to stabilize free radicals.
14 Free Radical Most free radicals are highly reactive substances they have an unpaired electronA free radical can remove an electron from a more stable molecule, such as DNA, a protein, or a polyunsaturated fatty acid.Insert Figure 8.2
15 How Do Antioxidants Work? By giving up an electron to a free radical, an antioxidant protects other molecules.Action stabilizes the free radicalBeta-carotene and vitamins E and C function as antioxidants.
17 Classifying Vitamins 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 toxicWater-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
20 Sources of Vitamins Natural Sources: Synthetic: Plants, animals, fungi, and bacteriaSynthetic:Made in laboratories by chemistsSynthesized by microbes in laboratories and extracted for commercial useMost natural and synthetic forms have equal activity in the body except:Natural vitamin E: greater biological activity than syntheticSynthetic folate: greater biological activity than natural
21 Vitamin Enrichment and Fortification Addition of specific amounts of thiamin, riboflavin, niacin, folic acid, and the mineral iron to refined flour and milled grainsGrains lose considerable amounts of theirnatural vitamin/mineral contents during refinementFortificationAddition of one or more nutrients to a wide array of commonly eaten processed foods during their manufacturing
22 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)PregnancyLactation (milk production)
23 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 (CF) interferes with fat digestion and fat-soluble vitamin absorptionPeople with CF and other intestinal diseases may need to take supplemental sources of vitamins.
24 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 practicesFood enrichment and fortificationWidespread availability of fruits and vegetablesAccording to dietary surveys: at least 25% of Americans consume inadequate amounts of A, E, and C.
25 Populations at Risk for Vitamin Deficiency (U.S.) AlcoholicsElderlyHospitalized (long-term)Anorexia nervosaCertain gastrointestinal disordersRare metabolic conditions
26 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:1) Length of time since harvest2) Storage conditions since harvest
27 Which Vitamins are Susceptible to Loss? Vitamin C, thiamin, and folate are easily destroyed by improper storage and preparation practices.Niacin and vitamin D tend to be very stable.
28 Ways to Maximize Vitamin Contents of Foods Avoid buying wilted, bruised, or shriveled produce.Store at near freezing temperatures, in high humidity and air-tight containers.Cook in small amounts of water.Avoid cutting foods that will be cooked into small pieces.Use quick cooking methods such as microwaving, steaming, and stir-frying.Freeze produce to preserve vitamins.
31 Vitamin A Retinol (preformed A) Beta-carotene (provitamin A) Most active form of the vitaminIn animal foodsBeta-carotene (provitamin A)One of a few carotenoids (plant pigments) that the body can convert to retinolMajor functionsNormal vision and reproductionCellular growthImmune system functionEpithelial cell production and maintenance
32 Vitamin A What is night blindness? The inability to see in dim light An early sign of vitamin A deficiencyThe 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.
34 Vitamin A Content of Selected Foods Insert Table 8.3
35 Vitamin A Dietary Adequacy Vitamin A Deficiency RDA: 700 - 900 mcg RAE Certain epithelial cells produce too much keratinKeratin - tough protein found in hair, nails, and outermost layers of skinExcess keratin:Skin becomes rough and bumpyInner eyelid cells that secrete mucus to protect cornea become keratinized.Can result in xeropthalmia “dry eye”
36 Xerophthalmia If untreated, vitamin A deficiency eventually leads to blindness.
37 What is Carotenemia? Carotenemia Yellowing of skin due to excessive beta-carotene intakeMay 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
38 Vitamin D Rickets: vitamin D deficiency in children - Results in soft bones that do not grow properly and become misshapen
39 Vitamin D: The “Sunshine Vitamin” Synthesis and Functions Insert Figure 8.10Vitamin D: The “Sunshine Vitamin” Synthesis and Functions
40 Why Is Vitamin D Necessary? Vitamin D is needed for:Metabolism of calcium and phosphorusProduction and maintenance of healthy bonesParathyroid hormone (PTH)Released when blood calcium levels dropStimulates kidneys to increase active vitamin D production and decrease urinary calcium excretion
41 Maintaining Normal Blood Calcium Levels Insert Figure 8.11
42 Vitamin D and Sunlight People who live south of the 37th parallel and areoutdoors when sunlightis most intense are mostlikely synthesizingadequate previtamin D.Insert Figure 8.12
43 Vitamin D Adequacy and Deficiency Dietary AdequacyAI: 5 mcg/day (200 IU) for people < 50 years of ageVitamin D DeficiencyRicketsRare in the U.S. because many foods are fortified with vitamin DMay develop in breastfed infantsOsteomalacia -- “adult rickets”
44 Vitamin D Toxicity Upper Limit (UL) Vitamin D toxicity 50 mcg/day (2000 IU)Vitamin D toxicityToo much calcium is absorbedThe excess calcium is deposited in soft tissues including kidneys, heart, and blood vessels.
45 Vitamin E Alpha-tocopherol Functions: Major fat-soluble antioxidant found in cellProtects polyunsaturated fatty acidsImproves vitamin A absorptionMaintains nervous system and immune system function
46 Selected Food Sources of Vitamin E Insert Table 8.5
47 Vitamin E Adequacy, Deficiency, and Toxicity Dietary AdequacyRDA: 15 mg/dayVitamin E DeficiencyHemolysis (breaking apart) of RBCDue to oxidation of polyunsaturated fatty acids in cell membraneVitamin E ToxicityUpper Limit (UL) 1000 mg/dayExcess may interfere with vitamin K’s role in blood clotting
48 Water-Soluble Vitamins Most function ascomponents ofspecific coenzymesCoenzymes: small molecules that regulate chemical reactions by interacting with enzymesInsert Figure 8.16Coenzymes are comprised of B vitamin and a nitrogen-containing substance
49 Coenzyme Function enzyme-coenzyme complex enables the Insert figure 8.16Once activated, theenzyme-coenzymecomplex enables thereaction to occur.
51 MyPyramid and the Water-Soluble Vitamins Insert Figure 8.17MyPyramid and the Water-Soluble Vitamins
52 Thiamin Functions Dietary Adequacy Deficiency Part of coenzyme involved in release of energy from carbohydratesMetabolism of certain amino acidsSynthesis of neurotransmittersDietary AdequacyRDA = 1.2 mg/day (men) 1.2 mg/day (women)DeficiencyNot storeddeficiency symptoms can occur within in a few days
53 Beriberi Thiamin deficiency condition People are weak, have poor muscular coordination, and may develop cardiovascular problems and edema.Insert figure 8.18
54 Selected Food Sources of Thiamin Insert Table 8.7
55 Riboflavin Functions Dietary Adequacy Deficiency Coenzyme for metabolism of carbohydrate, lipids, and amino acidsDietary AdequacyRDA = 1.3 mg/day (males) 1.1 mg/day (females)DeficiencyMay occur in people who do not drink milk or eat enriched grains
56 Selected Food Sources of Riboflavin Insert Table 8.8
57 Niacin Functions Dietary Adequacy Deficiency Part of two coenzymes that participate in at least 200 reactionsDietary AdequacyRDA = mg/dayDeficiencyPellagra—the “4 D’s” of pellagraDermatitis, Diarrhea, Dementia, Death
58 Selected Food Sources of Niacin Insert Table 8.9
59 Vitamin B-6 Functions Dietary Adequacy Deficiency Part of coenzyme needed for amino acid metabolismDietary AdequacyRDA = 1.3 to 1.7 mg/dayDeficiencyRarely occurs, but signs and symptoms include:Dermatitis, anemia, convulsions, depression, and confusion
61 Folate Folic Acid (synthetic) and Folacin Functions Part of coenzyme tetrahydrofolic acid (THFA)THFA involved in DNA and amino acid metabolismConversion of homocysteine to methionineGood Food Sources of FolateLeafy green vegetables, liver, legumes, asparagus, broccoli, and orangesDietary AdequacyRDA = 400 mcg DFE/day
62 Selected Food Sources of Folate Insert Table 8.11
63 Folate Deficiency Affects cells that rapidly divide, such as RBCs Mature RBCs do not have nuclei and live ~ 4 monthswithout folate, RBC precursor cells enlarge, but cannot divide (DNA is needed for division)Bone marrow releases some large, immature,abnormal RBCs with nuclei (megaloblasts)into the blood stream.
64 Red Blood Cell (RBC) Production Insert Figure 8.20
65 Neural Tube DefectsDuring 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.
66 Neural Tube Defects Two Common Types of Neural Tube Defects Spina bifidaSpinal bones do not form properly before birth and fail to enclose the spinal cord.AnencephalyBrain does not form properly or is missing.
67 Vitamin B-12 Functions Absorption of Dietary B-12 Part of coenzymes needed for:Folate metabolismMaintenance of myelin sheathsAbsorption of Dietary B-12B-12 in food is bound to proteinsHCL and pepsin required to release B-12 from proteinsB-12 must bind to intrinsic factor for absorption.
69 Selected Food Sources of Vitamin B-12 Insert Table 8.12
70 Vitamin B-12 Dietary Adequacy Deficiency RDA = 2.4 mcg/day Pernicious AnemiaGenetic defect reduces production of intrinsic factor and results in poor B-12 absorption.Signs and symptoms:megaloblastic anemia, nerve damage, weakness, sore tongue, memory loss, confusion, difficulty walking and maintaining balance, and eventual death
71 Vitamin C Functions — not part of a coenzyme Dietary Adequacy Collagen synthesisprotein that gives strength to connective tissuesAntioxidant activityOther Roles:Immune system functioningSynthesis of bile, and certain neurotransmitters and hormonesDietary AdequacyRDA = 75 to 90 mg/day (smokers have higher RDAs)
72 Selected Food Sources of Vitamin C Insert Table 8.13
73 Vitamin C Toxicity UL is 2000 mg/day Kidneys excrete excess amounts of the vitamin and oxalate, a byproduct of vitamin C metabolismIncreases risk of oxalate kidney stones, particularly in susceptible personsDeficiencyScurvyVery rare in U.S., because about 10 mg/day prevents scurvySigns and symptoms: poor wound healing, pinpoint hemorrhages, bleeding gums, bruises, and depression
74 Chapter 8 Highlight Megadosing on Vitamins Niacin As Medicine?UsesGiven to lower LDL cholesterol and raise HDL cholesterolSide effectsFlushing of skin on face and chest, itchy skin, GI tract upset, and liver damage
75 Vitamin B-6 As Medicine? Uses Side effects of high doses Claims include help for symptoms of PMS and carpal tunnel syndrome.Weak or no scientific support for claimsSide effects of high dosesSevere sensory nerve damageWalking difficultiesNumbness of hands and feetBecause of side effects, not recommended for treating PMS
76 Folic Acid As Medicine? Use Lowers blood homocysteine levels when taken with B-12 and B-6CVDRecent studies of subjects with CVD suggest folic acid supplements do not reduce risk of having heart another heart attack.Alzheimer’s diseaseMay be a relationship between mild cognitive impairment and folate deficiency or elevated blood homocysteineMore research is needed to determine whether taking supplements to lower homocysteine can reduce risk of cognitive decline or slow progression of Alzheimer’s.
77 Vitamin C As Medicine? Uses Does not prevent common cold but may reduce severity of the infectionReduces oxidation of LDL cholesterolMore research is needed to determine whether high doses help reduce CVD riskMore research is needed to determine whether vitamin C helps reduce cancer risk or aids in cancer treatment
78 Carotenoids As Medicine? UsesCancerOlder 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 riskDietary 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.
79 Vitamin E As Medicine? Questionable 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.
80 Some Final Thoughts 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.