Post on 25-Dec-2015
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The Vitamins
• Occur in smaller amounts than energy nutrients
• Yield no energy• Assist enzymes to release energy• Can only cure the disease caused
by a deficiency of that vitamin
© 2007 Thomson - Wadsworth
Bioavailability
• The availability of vitamins from foods
• Depends on– Quantity provided by the
food– Amount absorbed & used by
the body
• Other factors– Efficiency of digestion– Person’s previous nutrient intake &
nutrition status– Other foods eaten at the same time– Method of food preparation– Source of the nutrient (naturally
occurring, synthetic, or fortified)
© 2007 Thomson - Wadsworth
Other Terms
• Precursor– Inactive form of a
vitamin– Also called a provitamin– Must be converted to
the active form
• Solubility– Determines how a
vitamin is absorbed, transported, stored, & excreted
– Types • Fat-soluble• Water-soluble
© 2007 Thomson - Wadsworth
Fat-Soluble Vitamins
• A, D, E, & K• Occur in fats & oils• Absorbed the same way as lipids• Stored in liver & fatty tissues• Not readily excreted & can become toxic
© 2007 Thomson - Wadsworth
Vitamin A
• Retinoic acid• Is a hormone• Has a role in gene
expression• Regulates cell
differentiation• Maintains integrity of
epithelial cells• Retinol
• Supports reproduction
• Retinal– Active in vision– Maintains clear cornea– Participates in light
detection
• Has a role in immunity
© 2007 Thomson - Wadsworth
Beta-Carotene
• Is a plant-derived precursor
• Is an extremely effective antioxidant
• Antioxidants– Protect other compounds from
attack from oxygen– Free radicals can form from
oxidation– Oxidative damage & disease
• Age-related blindness• Alzheimer’s• Arthritis• Cataracts • Diabetes • Kidney disease
© 2007 Thomson - Wadsworth
Vitamin A Deficiency
• One year’s supply can be stored in the body
• Deficiency – Affects cell
differentiation & maturation
• Consequences of deficiencies– Hardening of cornea– Rough, scaly, hard skin– Drying & hardening of
salivary glands– Lumps of keratin around hair
follicles– Decreased immunity
© 2007 Thomson - Wadsworth
Vitamin A Toxicity
• Comes only from animal-derived vitamin A or supplements
• Children are very vulnerable• RDA
– 700 µg for women– 900 µg for men
• Multivitamins = 750-1500 µg
• Poses a teratogenic effect– Supplements – Acne treatments
• May weaken bones & contribute to osteoporosis
© 2007 Thomson - Wadsworth
Beta-Carotene Conversion & Toxicity
• Conversion– Losses occur when
converted to retinol– Measured in retinol
activity equivalents (RAE)– Body makes 1 unit of
retinol from 12 units of beta-carotene
• Toxicity– Not converted to active
form rapidly enough to be hazardous
– Can turn people bright yellow
– Builds up in fat beneath the skin
© 2007 Thomson - Wadsworth
Vitamin A in Foods
• Preformed vitamin A found only in animal foods
• Richest sources– Liver– Fish oil
• Other foods– Milk– Cheese– Fortified cereals– Butter– Eggs
• Margarine & fat-free milk are fortified with vitamin A
© 2007 Thomson - Wadsworth
Beta-Carotene in Foods
• Bold, dark orange color in fruits & vegetables
– Carrots– Sweet potatoes– Pumpkins– Cantaloupe– Apricots
• Dark green color in fruits & vegetables– Spinach– Other greens– Broccoli
• White plant foods have none
© 2007 Thomson - Wadsworth
Vitamin D
• Can be synthesized with help of sunlight– Liver manufactures a
precursor that migrates to skin
– Sun’s rays convert to second precursor
– Liver & kidneys produce active vitamin D
• Is a hormone
© 2007 Thomson - Wadsworth
Vitamin D’s Actions
• Target organs– intestine, kidneys, bones– Brain, pancreas, skin,
reproductive organs, many cancer cells
• Regulates the immune system
• Deficit implicated in– High blood pressure– Rheumatoid arthritis– Inflammatory bowel
disease– Multiple sclerosis
© 2007 Thomson - Wadsworth
Vitamin D’s Roles in Bone Health• Role
– Makes calcium & phosphorus available in the blood that bathes the bones
• Calcium & phosphorus– Stimulates absorption from GI tract– Releases from bones to blood– Stimulates retention by the kidneys
• Deficiency: rickets, osteomalacia, osteoporosis
© 2007 Thomson - Wadsworth
Vitamin D Deficiency
• Symptoms – Same as those of calcium deficiency– Rickets in children– Adult rickets (osteomalacia)– Risk factor for osteoporosis
© 2007 Thomson - Wadsworth
Vitamin D Toxicity
• Excess vitamin D– Enhances calcium
absorption– Produces high blood
calcium– Promotes return of bone
calcium into the blood
• Excess calcium can precipitate in soft tissue– Forms stones (kidney)– May harden blood
vessels
• Most toxic of all vitamins
© 2007 Thomson - Wadsworth
Vitamin D & the Sun
• Sun poses no toxicity risk• Does cause premature
wrinkling & risk of skin cancer
• Tanning booths– May stimulate vitamin D
production– Hazards outweigh benefits
© 2007 Thomson - Wadsworth
Vitamin D Deficiencies
• Persons at risk – Living in cloudy, smoggy areas– Housebound or institutionalized– Elderly & those on night shift – Persons with dark skin
• Sunscreen of 8 or greater SPF retards vitamin D synthesis
© 2007 Thomson - Wadsworth
Vitamin D in Foods
• Animal products– Eggs– Liver– Butter– Some fish– Fortified milk
• Fortified margarine & breakfast cereals
• Fortified infant formulas
• Breast milk is low in vitamin D– May need supplements
• Cheese & yogurt are not fortified
• Vegans may need supplements
© 2007 Thomson - Wadsworth
Vitamin E
• Fat-soluble antioxidant– Protects PUFA & other
lipids from oxidation– Protects lungs– May offer protection
from heart disease
• Myths: does not– Improve athletic skill– Enhance sexual
performance– Cure sexual dysfunction in
males– Prevent or cure muscular
dystrophy– Slow the aging process
© 2007 Thomson - Wadsworth
Vitamin E Deficiency
• Consequences– Erythrocyte hemolysis– Loss of muscle coordination &
reflexes• Associated with
– Diseases causing fat malabsorption
– Extremely low-fat diets– Diets of processed foods
© 2007 Thomson - Wadsworth
Vitamin E Toxicity
• Extremely high doses– Interfere with blood-clotting action of vitamin K– Enhance anticoagulant medications
• Research results are conflicting as to supplement safety– Tolerable Upper Intake Level =
1,000 mg– RDA = 15 mg
© 2007 Thomson - Wadsworth
Vitamin E in Foods
• Widespread in foods• 20% from vegetable oils• 20% from fruits &
vegetables• 15% from fortified
cereals & other grains
• Destroyed by heat processing & oxidation
© 2007 Thomson - Wadsworth
Vitamin K
• Roles– Blood clotting– Synthesis of several bone
proteins
• Can be synthesized by bacteria in intestine
• Deficiency is rare
• Vitamin K for newborns– Have a sterile digestive tract– Single dose of vitamin K
recommended at birth
• Toxicity– Is rare – High doses can interfere with
anticoagulant medications
© 2007 Thomson - Wadsworth
Vitamin K in Foods
• Green leafy vegetables
• Members of cabbage family
• Liver• Milk• Eggs
© 2007 Thomson - Wadsworth
Water-Soluble Vitamins
• B Vitamins– Thiamin– Riboflavin– Niacin– Pantothenic acid– Biotin– B6
– Folate – B12
• Vitamin C
• Easily absorbed• Easily excreted• Supplements can reach
toxic levels• B vitamins are
coenzymes– Combine with an
enzyme to make it active
© 2007 Thomson - Wadsworth
Coenzymes
• Release energy from fat, protein & carbohydrate – Thiamin– Riboflavin– Niacin– Pantothenic acid– Biotin
• Assist enzymes to metabolize amino acids– Vitamin B6
• Making of new cells– Folate coenzyme– Vitamin B12
© 2007 Thomson - Wadsworth
B Vitamin Deficiencies
• Deficiency of any single B vitamin seldom occurs
• Beriberi: deficiency of thiamin• Pellagra: deficiency of niacin• Sources of deficiencies in U.S.
– Poverty– Ignorance, illness – Alcohol abuse
© 2007 Thomson - Wadsworth
B Vitamins
• Interdependent Systems– All body systems depend on the B
vitamins– However, some systems use them to a
larger extent• Nerves & muscles depend on thiamin• Red blood cells & GI tract cells depend
on folate
© 2007 Thomson - Wadsworth
B Vitamins
• Enrichment of foods– Adding nutrients to a food to meet a specific
standard
• Fortification of foods– Addition of nutrients that were not originally
present or present in insignificant amounts
• Prevents B vitamin deficiencies
© 2007 Thomson - Wadsworth
Thiamin
• Needed for all cells– Critical role in energy
metabolism– Critical role in nerve & muscle
function
• Deficiency– Diet of empty kcalories, sugar
or alcohol– Wernicke-Korsakoff syndrome
© 2007 Thomson - Wadsworth
Riboflavin
• Facilitates energy production
• Needs increase during periods of rapid growth
• Is light sensitive & heat stable
© 2007 Thomson - Wadsworth
Niacin• Role in energy metabolism• Body can make it from tryptophan• Fairly heat resistant • Can be used as a medication to
lower blood cholesterol
© 2007 Thomson - Wadsworth
Biotin• Important in energy metabolism• Is a coenzyme that carries carbon dioxide• Participates in gene expression & cell signaling• Deficiency
– Alcohol abuse– Long-term use of anticonvulsant medication
• Wide-spread in foods
© 2007 Thomson - Wadsworth
Vitamin B6• Called the “sleeping giant”• Stored extensively in muscle tissue• Deficiency
– Weakening immune response– Weakness, irritability, & insomnia– Greasy, flaky dermatitis; anemia; convulsions
• Toxicity– Numbness of extremities
© 2007 Thomson - Wadsworth
Roles of Vitamin B6
© 2007 Thomson - Wadsworth
Coenzyme for more than 100 reactions involving nitrogen compounds:
Amino acid metabolism (transamination)
w/o PLP, every AA would be essential
Also converts homocysteine to AA cysteine
Heme synthesis
Carbohydrate metabolism (needed to release glucose from glycogen)
Neurotransmitter synthesis (5-HT from tryptophan, dopamine and NE from
tyrosine), histamine from histidine, and GABA from glutamic acid
Needed for formation of niacin from tryptophan
Immune function
Lipid metabolism
Folate
• Active in cell division• Increased need
during times of growth
• Deficiency causes– Anemia– GI tract deterioration
• Alcohol– Impairs absorption– Increases excretion
• Drugs – Aspirin, oral contraception, &
anticonvulsants– Impair folate status
• Smoking exerts a negative effect
© 2007 Thomson - Wadsworth
Folate
• Neural tube defects– Spina bifida &
anencephaly– Occur early in pregnancy– Folate is preventative– Women of childbearing
age need 0.4 mg/day
• May be related to cardiovascular disease risk
• Foods– Liver, legumes & leafy
green vegetables– Oranges, orange juice, &
cantaloupe– Fortified grains
© 2007 Thomson - Wadsworth
Vitamin B12
• Vitamin B12, folate, & cell division– B12 needed to activate
folate– Assists folate in cell
division– Deficiency of folate or B12
produces anemia
• Vitamin B12 & the Nervous System– Folate masks B12 deficiency
– Causes nerve deterioration, leading to paralysis & permanent nerve damage
• Concern about use of folate supplements & fortification of foods
© 2007 Thomson - Wadsworth
Vitamin B12
• Requires intrinsic factor for absorption
• Loss of intrinsic factor– Surgical removal of
stomach– Defective gene– May need injections
• Foods– Animal products
• Vegans/Deficiency– Receive none in the diet– Consume large amount of
folate– Deficiency takes years to
develop– Must take B12 supplements
© 2007 Thomson - Wadsworth
Inositol, Choline, Carnitine
• Are non-B vitamins• Serve as coenzymes in
metabolism• Are abundant in foods• May be essential
• Other non-B vitamins– PABA– bioflavonoids– ubiquinone
© 2007 Thomson - Wadsworth
Vitamin C: Metabolic Roles
• Collagen formation– Matrix of the bones– Material of scars– “Glue” that attaches one cell
to another
• Antioxidant– Protects water-soluble
substances from oxidation– Enhances iron absorption
• Amino acid metabolism
• Possible antihistamine– May reduce severity & duration of
cold & allergy symptoms
• Cancer prevention & treatment is being researched
• Role of Stress– Vitamin C needs increase
© 2007 Thomson - Wadsworth
Vitamin C Deficiency
• Latent scurvy– Gums bleed– Pinpoint hemorrhages in
skin
• Once diagnosed, scurvy is readily reversible– 100 mg/day
• Overt scurvy– Muscles including heart
may degenerate– Skin becomes rough,
brown, scaly, & dry– Wounds fail to heal– Fractures occur– Teeth become loose– Anemia & infections
© 2007 Thomson - Wadsworth
Vitamin C
• Toxicity– Megadoses = 10-30 times the
recommended intake• Symptoms/Consequences
– Nausea– Abdominal cramps– Diarrhea– Interference with warfarin &
dicumarol– Iron overload
• Safe limits = 100-300 mg/day
• Recommended Intake– Men = 90 mg– Women = 75 mg
• Special needs– Infections, burns, surgery,
extreme temperatures– Aspirin, barbiturates, oral
contraceptives, smoking
© 2007 Thomson - Wadsworth
Vitamin C
• Foods– Citrus fruits– Cantaloupe – Strawberries– Broccoli– Brussels sprouts– Organ meats: liver &
kidneys– Potatoes
• Is easily oxidized
• Iron absorption– Iron absorption can
double or triple if eaten with vitamin C-containing foods
– Highly recommended for women & children
© 2007 Thomson - Wadsworth
Phytochemicals
• Non-nutrient compounds found in plants
• Whole grains, legumes, vegetables, & fruits seem to be protective against heart disease & cancer
• Solid evidence about effects of phytochemicals is lacking
• Eat the food, not supplements
© 2007 Thomson - Wadsworth
Flavonoids
• A large group of phytochemicals
• Known for health-promoting qualities
• Found in– Whole grains– Vegetables– Fruits– Herbs – Spices– Teas– Red wine
© 2007 Thomson - Wadsworth
Carotenoids
• Red & yellow pigments of plants
• Beta-carotene– Vitamin A precursor– Associated with low risk
of heart disease
• Lycopene– Antioxidant – Found in guava, papaya,
pink grapefruit, tomatoes, watermelon
– May be protective against cancer
© 2007 Thomson - Wadsworth
Functional Foods
• Contain physiologically active components that provide health benefits beyond basic nutrition
• Have characteristics similar to both food & drugs
• Examples– Orange juice fortified with
calcium– Margarine fortified with
sterol esters
© 2007 Thomson - Wadsworth