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Lecture
Outline
Chapter 8
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Vitamins
Chapter 8
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chapter
Chapter Learning Outcomes
1. Classify vitamins according to whether they are fatsoluble 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

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?

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 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
How Vitamins Differ from
Carbohydrate, Fat, and Protein
Vitamins
Organic
No Calories
Micronutrients
Foods contain very
small amounts
(milligrams or micrograms)
Same
Differ
Carbs, Fats, Proteins
Organic
Provides Calories
Macronutrients
Foods contain
relatively large
amounts
(grams)
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
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
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.
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.
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
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.
Antioxidant Action
• Insert Figure 8.3
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
Fat-Soluble Vitamins
• Insert Table 8.1
Watersoluble
Vitamins
•
Insert Table 8.1
Sources of Vitamins
Natural Sources:
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
Vitamin Enrichment and Fortification
• Enrichment
– 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
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
• 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.
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.
Populations at Risk for Vitamin
Deficiency (U.S.)
•
•
•
•
•
Alcoholics
Elderly
Hospitalized (long-term)
Anorexia nervosa
Certain gastrointestinal
disorders
• Rare metabolic conditions
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
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.
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.
Summary: Fat-Soluble
Vitamins
• Insert Table 8.2
• Insert Figure 8.6
MyPyramid: Fat-Soluble Vitamins
Vitamin A
Retinol (preformed 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
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.
Vitamin A
and
Vision
• Insert Figure 8.7
Vitamin A Content of Selected
Foods
• Insert Table 8.3
Vitamin A
• Dietary Adequacy
– RDA: 700 - 900 mcg RAE
• Vitamin A Deficiency
– 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”
Xerophthalmia
If untreated, 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.
– Typically harmless
Vitamin D
Rickets: vitamin D deficiency in children
- Results in soft bones that do not grow
properly and become misshapen
• Insert Figure 8.10
Vitamin D: The “Sunshine Vitamin”
Synthesis and Functions
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
Maintaining Normal Blood Calcium Levels
• Insert Figure
8.11
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
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”
Vitamin D Toxicity
• Upper Limit (UL)
– 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.
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
Selected Food Sources of
Vitamin E
• Insert Table 8.5
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
Water-Soluble Vitamins
Most function as
components of
specific coenzymes
• Coenzymes: small
molecules that
regulate chemical
reactions by interacting
with enzymes
• Ins
ert
Fig
ure
8.1
6
Coenzymes are comprised
of B vitamin and a nitrogencontaining substance
Coenzyme
Function
Once activated, the
enzyme-coenzyme
complex enables the
reaction to occur.
Insert figure
8.16
Water-Soluble Vitamins
• Insert Table 8.8
• Insert Figure 8.17
MyPyramid and the Water-Soluble Vitamins
Thiamin
• Functions
– 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
Beriberi
• Thiamin deficiency
condition
• People are weak, have
poor muscular
coordination, and may
develop cardiovascular
problems and edema.
Insert figure
8.18
Selected Food Sources of
Thiamin
• Insert Table 8.7
Riboflavin
• Functions
– 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
Selected Food Sources of
Riboflavin
• Insert Table 8.8
Niacin
• Functions
– Part of two coenzymes that participate in at
least 200 reactions
• Dietary Adequacy
– RDA = 14-16 mg/day
• Deficiency
– Pellagra—the “4 D’s” of pellagra
Dermatitis, Diarrhea, Dementia, Death
Selected Food Sources of
Niacin
Insert Table 8.9
Vitamin B-6
• Functions
– 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
Selected Food Sources of B-6
Insert Table 8.10
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
Selected Food Sources of
Folate
• Insert Table 8.11
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.
Red Blood Cell (RBC) Production
• Insert Figure 8.20
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.
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.
Vitamin B-12
• Functions
– 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.
Vitamin B-12 Absorption
• Insert Figure 8.22
Selected Food Sources of
Vitamin B-12
• Insert Table 8.12
Vitamin B-12
• Dietary Adequacy
– RDA = 2.4 mcg/day
• Deficiency
– 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
Vitamin C
• Functions — not part of a coenzyme
– 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)
Selected Food Sources of
Vitamin C
• Insert Table 8.13
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
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
Vitamin B-6 As Medicine?
• Uses
– 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
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.
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
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.
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.
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.