chapter 8 the vitamins © 2007 thomson - wadsworth

Chapter 8

The Vitamins

© 2007 Thomson - Wadsworth

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


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)


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


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


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


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


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


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


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


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


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


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


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


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


Vitamin D Deficiency

• Symptoms – Same as those of calcium deficiency– Rickets in children– Adult rickets (osteomalacia)– Risk factor for osteoporosis


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


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


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


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


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


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


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


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


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


Vitamin K in Foods

• Green leafy vegetables

• Members of cabbage family

• Liver• Milk• Eggs


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


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


Coenzyme Action


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


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


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


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


Riboflavin

• Facilitates energy production

• Needs increase during periods of rapid growth

• Is light sensitive & heat stable


Niacin• Role in energy metabolism• Body can make it from tryptophan• Fairly heat resistant • Can be used as a medication to

lower blood cholesterol


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


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


Roles of Vitamin B6


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

Vitamin B6


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


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


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


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


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


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


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


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


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


Nutrition in Practice

Phytochemicals & Functional Foods


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


Flavonoids

• A large group of phytochemicals

• Known for health-promoting qualities

• Found in– Whole grains– Vegetables– Fruits– Herbs – Spices– Teas– Red wine


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


Functional Foods


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


chapter 8 the vitamins © 2007 thomson - wadsworth

Documents

thomson wadsworth slide

foods preformed vitamin

animal derived vitamin

foods bold

fatsoluble vitamins

body deficiency

active form solubility

unit of retinol