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Lecture Outline Chapter 8

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1 Lecture Outline Chapter 8
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2 Vitamins Chapter 8 Insert 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 False Natural vitamins are better for you because they have more biological activity than synthetic vitamins. T F Certain vitamins are toxic. T F Vitamin E is an antioxidant. T F Vitamins 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 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

7 Vitamins: Basic Concepts
Most 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. Beta-carotene (plant pigment) = precursor to vitamin A Tryptophan = (amino acid) precursor to B-vitamin niacin

8 How Vitamins Differ from Carbohydrate, Fat, and Protein
Organic No Calories Micronutrients Foods contain very small amounts (milligrams or micrograms) Carbs, Fats, Proteins Organic Provides Calories Macronutrients Foods contain relatively large amounts (grams) Same Differ

9 Vitamins Are Micronutrients
Comparing Amounts of Nutrients in a Food A slice of bread weighs about 1 oz (28 g) Vitamins comprise only ~0.005% (1.48 mg) of the bread’s weight Insert slice of bread from page 224

10 Roles of Vitamins Vitamins may: Have hormonal action (e.g., vitamin D)
Participate in certain chemical reactions Regulate certain body processes Cell division and development Growth and maintenance of tissues

11 Vitamins and Their Functions
Insert figure 8.1

12 Do Vitamins Supply Any Calories?
Vitamins do not supply energy, but many participate in the chemical reactions that release the energy stored in macronutrients.

13 What is an Antioxidant? Oxidation = loss of electrons
Reduction = gain of electrons Oxidation 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 electron A 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 radical Beta-carotene and vitamins E and C function as antioxidants.

16 Antioxidant Action Insert Figure 8.3

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 toxic 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

18 Fat-Soluble Vitamins Insert Table 8.1

19 Water-soluble Vitamins
Insert Table 8.1

20 Sources of Vitamins Natural Sources: Synthetic:
Plants, animals, fungi, and bacteria 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: greater biological activity than synthetic Synthetic 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 grains Grains lose considerable amounts of their natural vitamin/mineral contents during refinement Fortification Addition 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) Pregnancy Lactation (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 absorption People 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 practices Food enrichment and fortification Widespread availability of fruits and vegetables According 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.)
Alcoholics Elderly Hospitalized (long-term) Anorexia nervosa Certain gastrointestinal disorders Rare 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 harvest 2) 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.

29 Summary: Fat-Soluble Vitamins
Insert Table 8.2

30 MyPyramid: Fat-Soluble Vitamins
Insert Figure 8.6 MyPyramid: Fat-Soluble Vitamins

31 Vitamin A Retinol (preformed A) Beta-carotene (provitamin A)
Most active form of the vitamin In animal foods Beta-carotene (provitamin A) 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

32 Vitamin A 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. Rods and cones need vitamin A to function properly.

33 Vitamin A and Vision Insert Figure 8.7

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 keratin Keratin - tough protein found in hair, nails, and outermost layers of skin Excess keratin: Skin becomes rough and bumpy Inner 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 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. 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 8.10 Vitamin D: The “Sunshine Vitamin” Synthesis and Functions

40 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

41 Maintaining Normal Blood Calcium Levels
Insert Figure 8.11

42 Vitamin D and Sunlight People who live south of
the 37th parallel and are outdoors when sunlight is most intense are most likely synthesizing adequate previtamin D. Insert Figure 8.12

43 Vitamin D Adequacy and Deficiency
Dietary Adequacy AI: 5 mcg/day (200 IU) for people < 50 years of age Vitamin D Deficiency Rickets Rare in the U.S. because many foods are fortified with vitamin D May develop in breastfed infants Osteomalacia -- “adult rickets”

44 Vitamin D Toxicity Upper Limit (UL) Vitamin D toxicity
50 mcg/day (2000 IU) Vitamin D toxicity Too much calcium is absorbed The 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 cell Protects polyunsaturated fatty acids Improves vitamin A absorption Maintains 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 Adequacy RDA: 15 mg/day Vitamin E Deficiency Hemolysis (breaking apart) of RBC Due to oxidation of polyunsaturated fatty acids in cell membrane Vitamin E Toxicity Upper Limit (UL) 1000 mg/day Excess may interfere with vitamin K’s role in blood clotting

48 Water-Soluble Vitamins
Most function as components of specific coenzymes Coenzymes: small molecules that regulate chemical reactions by interacting with enzymes Insert Figure 8.16 Coenzymes are comprised of B vitamin and a nitrogen-containing substance

49 Coenzyme Function enzyme-coenzyme complex enables the
Insert figure 8.16 Once activated, the enzyme-coenzyme complex enables the reaction to occur.

50 Water-Soluble Vitamins
Insert Table 8.8

51 MyPyramid and the Water-Soluble Vitamins
Insert Figure 8.17 MyPyramid and the Water-Soluble Vitamins

52 Thiamin Functions Dietary Adequacy Deficiency
Part of coenzyme involved in release of energy from carbohydrates Metabolism of certain amino acids Synthesis of neurotransmitters Dietary Adequacy RDA = 1.2 mg/day (men) 1.2 mg/day (women) Deficiency Not stored deficiency 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 acids Dietary Adequacy RDA = 1.3 mg/day (males) 1.1 mg/day (females) Deficiency May 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 reactions Dietary Adequacy RDA = mg/day Deficiency Pellagra—the “4 D’s” of pellagra Dermatitis, 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 metabolism Dietary Adequacy RDA = 1.3 to 1.7 mg/day Deficiency Rarely occurs, but signs and symptoms include: Dermatitis, anemia, convulsions, depression, and confusion

60 Selected Food Sources of B-6
Insert Table 8.10

61 Folate Folic Acid (synthetic) and Folacin Functions
Part of coenzyme tetrahydrofolic acid (THFA) THFA involved in DNA and amino acid metabolism Conversion of homocysteine to methionine Good Food Sources of Folate Leafy green vegetables, liver, legumes, asparagus, broccoli, and oranges Dietary Adequacy RDA = 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 months without 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 Defects 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.

66 Neural Tube Defects Two Common Types of Neural Tube Defects
Spina bifida Spinal bones do not form properly before birth and fail to enclose the spinal cord. Anencephaly Brain does not form properly or is missing.

67 Vitamin B-12 Functions Absorption of Dietary B-12
Part of coenzymes needed for: Folate metabolism Maintenance of myelin sheaths Absorption of Dietary B-12 B-12 in food is bound to proteins HCL and pepsin required to release B-12 from proteins B-12 must bind to intrinsic factor for absorption.

68 Vitamin B-12 Absorption Insert Figure 8.22

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 Anemia Genetic 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 synthesis protein that gives strength to connective tissues Antioxidant activity Other Roles: Immune system functioning Synthesis of bile, and certain neurotransmitters and hormones Dietary Adequacy RDA = 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 metabolism Increases risk of oxalate kidney stones, particularly in susceptible persons Deficiency Scurvy 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

74 Chapter 8 Highlight Megadosing on Vitamins
Niacin As Medicine? Uses Given to lower LDL cholesterol and raise HDL cholesterol Side effects Flushing 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 claims Side effects of high doses Severe sensory nerve damage Walking difficulties Numbness of hands and feet Because 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-6 CVD Recent studies of subjects with CVD suggest folic acid supplements do not reduce risk of having heart another heart attack. Alzheimer’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.

77 Vitamin C As Medicine? Uses
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 risk More research is needed to determine whether vitamin C helps reduce cancer risk or aids in cancer treatment

78 Carotenoids As Medicine?
Uses Cancer 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 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.

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.


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