Ch 6 ppt

CHAPTER 6
Vitamins

Eleanor D. Schlenker

Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc.

Vitamins
 Criteria used to define a compound as a
vitamin:
 It must be an organic dietary substance that is not
an energy-producing carbohydrate, fat, or protein
 It is needed in very small quantities to perform a
particular metabolic function or prevent an
associated deficiency disease
 It cannot be manufactured by the body and
therefore must be supplied in food

Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 2

Vitamins: Basic Concepts
 As our understanding of vitamins has
expanded, the following important concepts
have emerged:
 Individual vitamins are multifunctional
 One vitamin cannot substitute for another vitamin
 Vitamins work together in carrying out body
functions
 Vitamins function best when all are present in the
appropriate proportions


Classification of Vitamins
 Vitamins have been grouped according to
their solubility in either fat or water
 Fat-soluble vitamins
• A, D, E, and K
• Closely associated with body lipids and are easily stored
 Water-soluble vitamins
• Vitamin C and the B-complex family
• Easily absorbed and transported
• Cannot be stored except in the general sense of tissue
saturation


Fat-Soluble Vitamins
Vitamin A
 Generic name for a group of compounds

having similar biologic activity: retinol, retinal,
and retinoic acid


Fat-Soluble Vitamins – Cont’d
 There are two dietary forms of vitamin A:
1. Preformed vitamin A (retinol)
• Natural form of vitamin A found only in animal foods and
usually associated with fat
2. Provitamin A (beta-carotene)
• Plants cannot synthesize vitamin A but instead produce a
family of compounds called carotenoids
• Beta-carotene, converted to vitamin A in the body,
provides about 21% of the total vitamin A intake in the
United States
• Poor conversion of carotenoids to vitamin A may
contribute to vitamin A deficiency in developing countries
where persons depend on plant sources


Absorption of Vitamin A
 Various materials are needed for the
absorption of vitamin A or beta-carotene:
 Bile salts
 Pancreatic lipase
 Dietary fat


Conversion of Beta-Carotene
 Beta-carotene can be absorbed and used by
the body in its original form or be converted to
vitamin A
 Carotenoids are important both as vitamin A
precursors and as phytochemicals


Transport and Storage of Vitamin
A
 The route of absorption of both vitamin A and
the carotenoids parallels that of fat
 The liver contains up to 85% of the body’s
total supply of Vitamin A
 A prophylactic dose of vitamin A every 6
months prevents deficiency in developing
countries


Functions of Vitamin A
 Visual adaptation to light and darkness
 Generalized actions that affect the integrity of:
 Body coverings and linings (epithelial tissues)
 Growth
 Immune response
 Reproductive function


Vitamin A Deficiency

 Vision
 Normal rhodopsin cannot be made and the rods
and cones of the retina become increasingly
sensitive to changes in light, causing night
blindness
 Reversed with retinol injection


Vitamin A Deficiency – Cont’d

 Cell differentiation
 Keratinization: dry and flat cells
• Eye—xerophthalmia and blindness
• Respiratory tract—dryness and loss of cilia
• Gastrointestinal tract—dryness, poor digestion, and
absorption
• Skin—dry and scaly, follicular hyperkeratosis
• Tooth formation—ameloblasts do not develop


Vitamin A Deficiency – Cont’d
 Growth
 Essential for growth of bones and soft tissues
 Controls protein synthesis and mitosis
 Excessive intakes also cause poor bone health
 Reproduction
 Normal sexual maturation and function
 Gene expression and fetal development
 Immunity
 Lack of epithelial and mucosal barrier
 Direct effect on cell-mediated and antibody-mediated
immunity


Vitamin A Requirement
Influencing Factors
 A number of variables can modify the vitamin

A needs of a given individual:
 Liver stores
 Intake of preformed versus provitamin A
 Illness and infection
 Gastrointestinal or hepatic defects


Vitamin A Requirement – Cont’d

Causes of Vitamin A Deficiency
 Inadequate dietary intake

 Poor food selection and fast food
 Poor absorption or metabolism
 Lack of bile or dietary fat
 Inadequate conversion of beta-carotene
 Liver or intestinal disease

 High intake of alcohol


Vitamin A Requirement – Cont’d

Recommended Dietary Allowance (RDA)
 For vitamin A the RDA is the amount required

to maintain optimum liver stores
 The RDA for men ages 19 and over is set at 900 µg
 The RDA for women of this age is 700 µg
 The RDA increases to 770 µg in pregnancy and
1300 µg in lactation


Vitamin A Toxicity
 Hypervitaminosis A
 High-potency supplements
 UL is 3000 µg/day
 Especially dangerous in pregnancy


Food Sources of Vitamin A
 Animal sources:
 Liver, milk, cheese, butter, egg yolk, and fish
 Nonanimal products:
 Margarine, ready-to-eat cereals, and cereal bars
are being fortified with vitamin A
 Deep yellow, orange, red, and dark green
vegetables and fruits, contain carotenoid
precursors of vitamin A
 Carotenoids are more available from cooked
vegetables



Vitamin D
 A prohormone and in its active form functions as

a hormone
 Chemically, vitamin D is a sterol and its

precursor found in human skin is the lipid
molecule 7-dehydrocholesterol


Vitamin D – Cont’d
 Two forms:

1. Ergocalciferol (vitamin D2)
• Formed by irradiating ergosterol found in ergot (a
fungus growing on rye and other cereal grains) and
yeast
2. Cholecalciferol (vitamin D3)
• Formed by the action of ultraviolet light from the sun on
the 7-dehydrocholesterol in the skin
• Found naturally in fish liver oils


Vitamin D
Absorption
 Absorbed in the small intestine along with fat

 Malabsorption diseases, such as celiac
disease, cystic fibrosis, and Crohn’s disease
or pancreatic insufficiency, hinder vitamin D
absorption


Vitamin D – Cont’d
Active Hormone Synthesis
 1,25-dihydroxycholecalciferol [1,25(OH)2D3]

has the chemical name of calcitriol
 Calcitriol is produced by the combined action of
the skin, liver, and kidneys, an overall process
referred to as the vitamin D endocrine system
 Vitamin D3 is used and metabolized in the same
way whether obtained from skin synthesis or from
food


Functions of Vitamin D Hormone
 Associated with calcium and phosphorus
metabolism and their absorption and
deposition in bone tissue
 Acts on many tissues and functions
throughout the body
 Cell growth
 Muscle strength
 Immune function
 Insulin levels
 Hypertension and cardiovascular disease


Vitamin D Deficiency
Bone Disease
 Without sufficient vitamin D, the body cannot
absorb the calcium needed to build normal
bones
 Children develop rickets

 Adults develop osteomalacia

 Osteoporosis has different causes

 Breastfed infants need vitamin D
supplements
 Role in renal osteodystrophy


Vitamin D Requirements
Dietary Reference Intake
 Needs are affected by sun exposure and skin

synthesis
 Vitamin D has an Adequate Intake (AI), not

an RDA
 Persons between 6 months and 50 years of
age need 5 µg (200 IU)


Vitamin D Requirements – Cont’d
Dietary Reference Intake – Cont’d
 For persons 51 to 70 years, the AI increases

to 10 µg (400 IU)
 For those ages 71 and older, it increases to

15 µg (600 IU)
 The elevated AI for those over age 70 points to
their critical need to maintain bone mass and their
limited ability to synthesize vitamin D in their skin


Food Sources of Vitamin D
 Fatty fish such as mackerel
 A small amount occurs in egg yolk
 Vitamin D-fortified milk, margarine, juices,
and ready-to-eat cereals
 Vitamin D2 is found only in yeast
 Vitamin D3 is found mostly in fish liver oils
and is the form added to fortified foods


Vitamin E
 Vitamin E is the generic name given to a

group of compounds with similar physiologic
activity
 Includes eight fat-soluble, 6-hydroxychroman
compounds having some degree of the biologic
activity of alpha-tocopherol


Absorption
 Absorbed in the micelles with the aid of bile

 Stored in the liver and adipose tissue, where
it is held in bulk liquid droplets


Functions of Vitamin E
 Acts as an antioxidant in destroying
molecules called free radicals
 Free radicals are elements or molecules with
unpaired electrons that attack double bonds
in membranes and other body tissues


Functions of Vitamin E – Cont’d
 Changes caused by the “oxidation” of these
double bonds affects the function of these
membranes and tissues
 Partners with selenium
 Unproven role in preventing chronic disease
and aging changes in tissues
 May ameliorate toxicity associated with
chemotherapy


Vitamin E Deficiency
 Disastrous effects on red blood cells
 This vitamin E deficiency disease is called
hemolytic anemia
 Sometimes observed in newborns
 Disrupts the making of myelin, the protective
lipid covering of the nerve cell axons
 Degeneration of the pigment in the rods and
cones of the retina


Vitamin E Requirement
Dietary Reference Intakes
 Approximately 80% of the vitamin E from

dietary sources, including fortified foods, is
alpha-tocopherol
 Approximately 20% comes from other forms
 RDA for ages 14 and older:
 15 mg for males and females


Food Sources of Vitamin E
 Richest dietary sources of vitamin E are
vegetable oils
 Sunflower, safflower, canola, corn, and olive
oils
 Nuts and peanut butter
 Certain vegetables and fruits, especially
tomatoes
 Fortified ready-to-eat cereals


Vitamin K
 Forms

 Phylloquinone
• Found in plants, named for its chemical structure
• Major dietary form and is widely distributed in both
animal and vegetable foods
 Menaquinone
• Synthesized by intestinal bacteria
 Menadione
• Water-soluble analogue of vitamin K, can be absorbed
directly into the portal blood


Absorption of Vitamin K
 Phylloquinone and menaquinone require
pancreatic lipase and bile salts for absorption
 Packaged in the intestinal chylomicrons
 Travel via the lymphatic system and then the
portal blood to the liver
 In the liver, vitamin K is stored in small
amounts
 Rapidly excreted after administration of
therapeutic doses


Functional Roles of Vitamin K
Blood Clotting
 Initiates the synthesis of four blood-clotting

factors in the liver
 Controls the liver synthesis of other proteins

that regulate the speed and duration of
coagulation
Bone Metabolism
 Stimulates the synthesis of osteocalcin and

other proteins that are important in bone


Vitamin K Deficiency and Clinical
Application
 Neonatology
 Prophylactic dose soon after birth
 Malabsorption problems
 Defects in fat absorption impair vitamin K
absorption
 Drug therapy
 Anticlotting drugs require consistent intake of
vitamin K


Vitamin K Requirement
 AI for men ages 19 and over is 120 µg/day

 AI for women ages 19 and over is 90 µg/day

 This amount of vitamin K is adequate to
preserve blood clotting
 Unsure how much is needed for optimum

bone health


Food Sources of Vitamin K

 Phylloquinone is found in many vegetables,
highest in dark green vegetables and liver
 Menaquinones occur in milk, meat, and
certain cheeses


Water-Soluble Vitamins
Vitamin C
 Associated with the search for the cause of

the ancient hemorrhagic disease scurvy
Absorption, Transport and Storage
 Easily absorbed from the small intestine but

requires the presence of acid
 Distributed throughout body tissues

 Excess is excreted in the urine


Functions of Vitamin C
 Antioxidant
 Helps to take up the free oxygen arising from cell
metabolism, making it unavailable to fuel the
destructive actions of free radicals
 Formation of intercellular cement
 Helps build and maintain many body tissues,
including bone matrix, cartilage, dentin, collagen,
and connective tissue


Functions of Vitamin C – Cont’d
 Support of general body metabolism
 Important in many metabolically active tissues
 Helps in the formation of hemoglobin and the
development of red blood cells by:
1. Promoting iron absorption
2. Assisting in the removal of iron from the protein-iron
complex called ferritin
 Assists carnitine synthesis
 Assists peptide hormone synthesis
 Breakdown of drugs and other foreign molecules


Functions of Vitamin C – Cont’d
Clinical Applications
 Wound healing

 Fever and infection

 Growth

 Stress and body response

 Chronic disease prevention


Vitamin C Requirement
 Current Dietary Reference Intake takes into

account the need for antioxidant protection of
body tissues
 For men the RDA is 90 mg

 For women the RDA is 75 mg

 Cigarette smokers require an additional 35
mg each day


Food Sources of Vitamin C
 Best known food sources of vitamin C are
citrus fruits and tomatoes
 Broccoli, salad greens, strawberries,
watermelon, cabbage, and sweet potatoes
are other good sources


The B Vitamins
 All water soluble but with unique metabolic
functions
 Serve as coenzyme partners with cell
enzymes that control energy metabolism and
build tissues
 Thiamin, riboflavin, and niacin associated
with classic deficiency diseases


The B Vitamins – Cont’d
 Recently discovered coenzyme factors—
vitamin B6 (pyridoxine), pantothenic acid, and
biotin
 Important blood-forming factors—folate and
vitamin B12 (cobalamin)


Thiamin
 A water-soluble and fairly stable vitamin
 Destroyed in alkaline solutions
 Name comes from its chemical ringlike
structure (thiazole ring)


Thiamin – Cont’d
 Absorbed efficiently in the acid environment
of the upper small intestine before the acidity
of the food mass is buffered by the alkaline
secretions from the pancreas
 Carbohydrate increases the need for thiamin,
whereas fat and protein spare thiamin


Functions of Thiamin
 Control agent in energy metabolism
 Combines with phosphorus to form hiamin
pyrophosphate (TPP)
 TPP serves as a coenzyme in key reactions
involving glucose


Deficiency Symptoms of Thiamin

 Classic deficiency disease is beriberi
 Gastrointestinal: anorexia, constipation,
gastric atony, and poor HCl secretion
 Nervous: Diminished alertness and reflex
responses, general apathy, and fatigue
 Cardiovascular: Heart muscle weakens,
leading to cardiac failure and edema
 Musculoskeletal: Chronic pain


Thiamin Requirement
 Minimum requirement is 0.3 mg/1000 kcal

 RDA is set at 1.2 mg for adult men and 1.1
mg for adult women
 Extra is needed during pregnancy and

lactation
 Excess thiamin is excreted by the kidneys

 No UL has been established


Clinical Conditions That Influence
Thiamin Needs
 Alcohol abuse
 Acute illness or disease
 Normal growth and development
 Use of diuretics
 Gastric bypass surgery


Food Sources of Thiamin
 Widespread in plant and animal foods
 Major sources in the American diet:
 Whole and enriched breads and ready-to-eat
cereals, and legumes
 Good food sources include lean pork and
beef


Riboflavin

 Yellow-green fluorescent pigment that forms
yellowish brown, needlelike crystals
 Easily destroyed by light and irradiation


Absorption of Riboflavin
 Absorbed in the upper section of the small
intestine
 Hindered by bulk fiber supplements such as
psyllium
 Small amounts stored in the liver and kidney


Functions of Riboflavin
 Part of the cell enzymes called flavoproteins
 Active in both energy production and
deamination
 Deamination is the removal of a nitrogen-
containing amino group from an existing amino
acid so a new amino acid can be formed


Deficiency Symptoms of
Riboflavin
 Results in the condition termed
ariboflavinosis
 Tissue inflammation and breakdown and poor
healing of even minor injuries
 Sometimes occurs in newborns
 Riboflavin is destroyed by light and so deficiency
can occur in infants treated with phototherapy


Riboflavin Requirement
 RDA based on the amount needed to sustain

optimum levels of the flavoprotein enzymes
 1.3 mg/day for adolescent and adult men
 1.1 mg/day for adolescent and adult women
 No UL set, but high-dose supplements still
carry a risk


Riboflavin Requirement – Cont’d
Risk Groups
 Patients on hemodialysis

 Pregnant and lactating women and infants
and children
 People who engage in regular physical

activity


Food Sources of Riboflavin
 Major sources of riboflavin are milk and
cheese
 Riboflavin is destroyed by exposure to light;
therefore milk is usually packaged in cardboard or
opaque plastic containers
 Breast milk stored in clear glass or plastic
containers may lose riboflavin
 Other good sources of riboflavin are meat,
whole or enriched grains and ready-to-eat
cereals, and vegetables


Niacin
 In 1937 a researcher at the University of
Wisconsin associated niacin with pellagra by
using it to cure a related disease (black
tongue) in dogs
 Two forms of niacin have been identified:
1. Nicotinic acid
2. Nicotinamide


Niacin – Cont’d
 Stable to acid and heat
 Forms a white powder when crystallized
 The amino acid tryptophan can be converted
to niacin in the body
 60 mg tryptophan can produce 1 mg niacin
 Measured in niacin equivalents (NE)


Functions of Niacin
 Two coenzyme forms
1. Nicotinamide-adenine dinucleotide (NAD)
2. Nicotinamide-adenine dinucleotide phosphate
(NADP)
 Partners with riboflavin in systems that
convert amino acids and glycerol to glucose
and oxidize the glucose to release energy


Functions of Niacin – Cont’d
 Pharmacologic dosages of nicotinic acid have
been prescribed for cardiovascular patients in
an effort to raise blood high-density
lipoprotein (HDL) cholesterol levels and
reduce blood low-density lipoprotein (LDL)
cholesterol and triglyceride levels
 This treatment carries some degree of risk
and requires careful supervision
 At high levels, niacin is a vasodilator


Niacin Requirement
 RDA measured in niacin equivalents (NE)

 16 mg NE/day for adolescent and adult men

 14 mg NE/day for adolescent and adult
women


Niacin Requirement – Cont’d
 Increase in niacin is needed for the following:
 Rapid growth
 Pregnancy and lactation
 Physical activity
 Tissue replacement after surgery or trauma


Food Sources of Niacin
 Meat and dairy products are major sources of
niacin and also high in tryptophan
 Other foods include peanuts, dried beans and
peas, and whole grain or enriched breads
and cereals
 Corn and rice are relatively poor sources
because they are low in tryptophan


Pantothenic Acid
 Synthesized by intestinal bacteria and
present in a wide variety of foods
 Deficiency is unlikely
Absorption and Metabolism
 Absorbed in the intestine and combines with

phosphorus to make the active molecule
acetyl coenzyme A (CoA)
 No known toxicity or natural deficiency


Pantothenic Acid – Cont’d
Functions
 Controls metabolic reactions involving

carbohydrates, fat, and protein
Requirements
 5 mg/day for all adults will replace the

pantothenic acid lost daily in the urine
Food Sources
 Found in both plant and animal foods

 Good sources include egg yolk, milk, and broccoli


Biotin
 Sulfur-containing vitamin
 Natural deficiency is unknown
 May occur in patients receiving long-term total
parenteral nutrition without biotin
 Avidin, a protein found in raw egg white,
binds biotin and prevents its absorption
 Cooking denatures this protein and destroys its
ability to bind biotin
 No known toxicity for biotin


Biotin – Cont’d
Functions
 Partners with acetyl coenzyme A (CoA) in
reactions that transfer carbon dioxide from
one compound to another
 Synthesis of fatty acids
 Carbon dioxide fixation to form purines
Requirements
 30 µg/day for all adults

 Intestinal bacterial synthesis also adds to the
body’s supply


Food Sources of Biotin
 Found in many foods
 Bioavailability varies greatly
 Biotin in corn and soy is well absorbed
 Biotin in wheat is generally unavailable


Vitamin B6 (Pyridoxine)
 Chemical structure of vitamin B6 is a pyridine
ring
 Three forms occur in nature:
 Pyridoxine, pyridoxal, and pyridoxamine
 All three forms are equally active in the body as
precursors of the coenzyme pyridoxal phosphate
(B6-PO4), or PLP


Absorption of Vitamin B6
(Pyridoxine)
 Absorbed in the upper segment of the small
intestine
 Stored in muscle but found in tissues
throughout the body


Functions of Vitamin B6
 Coenzyme in more than 100 amino acid
reactions involving the synthesis of important
proteins:
 Neurotransmitters
 Amino group transfer
 Sulfur transfer
 Niacin
 Hemoglobin
 Immune function


Functions of Vitamin B6 – Cont’d
 Coenzyme in fat metabolism
 PLP converts the essential fatty acid linoleic acid
to arachidonic acid


Vitamin B6 Deficiency
 Vitamin B6 holds a key to a number of clinical
problems:
 Anemia
 Central nervous system changes
 Physiologic demands in pregnancy
 Blood homocysteine levels
 Medications


Vitamin B6 Requirement
 High protein intake increases the need for

vitamin B6
 Men and women ages 19 to 50 years need 1.3
mg/day
 Men over age 50 require 1.7 mg/day, and women
of this age require 1.5 mg/day


Vitamin B6 Toxicity
 Toxicity in women taking supplements 1000
times the RDA to alleviate premenstrual
syndrome
 Interferes with muscle coordination and
damages the nervous system
 UL is 100 mg/day


Food Sources of Vitamin B6
 Many foods contain pyridoxine in small
amounts
 Good sources include whole or fortified grain
products, legumes, meat, poultry, bananas,
and potatoes
 Highest contributor of pyridoxine to the diets
of U.S. adults is ready-to-eat cereals


Folate

 Named from Latin word for leaf because it
was first extracted from dark leafy vegetables
 Folic acid is seldom found naturally but is
used in supplements
 85% absorbed
 Naturally occurring food folate is
pteroylpolyglutamate
 50% absorbed


Functions of Folate
 Folate is the coenzyme with the important
task of attaching single carbons to metabolic
compounds
 Key molecules formed in this process include:
 Purines
 Thymine
 Hemoglobin


Folate Deficiency

Factors Associated With Folate Deficiency
 Lack of gastric acid

 Chemotherapy

 Anticonvulsant medications


Folate Deficiency – Cont’d

Clinical Implications of Folate Deficiency
 Anemia that responds to folate supplementation

 Most likely in pregnant women, growing infants, and
young children
 Inappropriately high blood homocysteine levels:
 Uncertain effects on cardiovascular disease,
osteoporosis, and age-related cognitive impairment


Folate Requirements
Folate and Birth Defects
 Plays essential role in the formation and

closure of the neural tube in the early weeks
of fetal development
 Demands that mother be in good folate status

before becoming pregnant; supplementation
after pregnancy is confirmed too late to
prevent damage to the fetus


Folate Requirements – Cont’d
Folate and Birth Defects – Cont’d
 Folate deficiency early in pregnancy can

result in a neural tube defect in the
developing fetus
 Mandatory folate fortification of flour or uncooked
grain
 Incidence of NTDs has declined
 Concern that it may mask vitamin B12 deficiency


Folate Requirements – Cont’d
 RDA for adolescents and adults of all ages is

400 µg/day
 Increases to 600 µg/day in pregnancy to

support fetal and maternal tissue growth
 Women of childbearing age should consume
at least 400 µg/day of folate
 Fortification has increased intakes by as

much as 200 µg/day


Food Sources of Folate
 Good sources include dark green leafy
vegetables, citrus fruits, tomatoes,
cantaloupe, and legumes
 Fortified grains and ready-to-eat cereals are
important sources


Vitamin B12 (Cobalamin)
 A complex red crystal of high molecular
weight with a single cobalt atom at its core
 Occurs as a protein complex in foods of
animal origin only


Absorption of Vitamin B12
(Cobalamin)
 Gastric acid is required to separate the
vitamin from its protein complex
 Vitamin is bound to a specific glycoprotein
called intrinsic factor secreted by the mucosal
cells lining the stomach
 Intestinal absorption occurs in the ileum


Functions of Vitamin B12
 Participates in amino acid metabolism and
the formation of the heme portion of
hemoglobin
 Involved in the synthesis of important lipids
and proteins that form the myelin sheath
covering the nerves of the brain and spinal
cord


Vitamin B12 Deficiency

Deficiency Symptoms
 Disrupted formation of red blood cells,
resulting in production of megaloblastic cells
(megaloblastic anemia)
 Damage to the nerves of the brain and spinal
cord with changes in cognitive function,
judgment, and personality


Vitamin B12 Deficiency – Cont’d
Deficiency Diseases
 Pernicious anemia

 Results from lack of intrinsic factor
 Treated with injections of vitamin B12


Vitamin B12 Deficiency – Cont’d
Deficiency Diseases – Cont’d
 Vitamin B12 deficiency in older adults

 Results from a lack of gastric acid
 Treated with injections of vitamin B12 or use of B12
fortified foods (this form of B12 does not require
gastric acid for absorption)
 Excessively high blood folate levels
ameliorate anemia, but exacerbate cognitive
losses


Vitamin B12 Requirements
 Needed in minute amounts
 RDA is 2.4 µg for both younger and older
adults


Food Sources of Vitamin B12

 Found naturally only in animal foods
 Rich sources include lean meat, fish,
poultry, milk, eggs, and cheese
 Vitamin B12—fortified grains, cereals,
juices, and soy milk or supplements


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