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9
THE FAT-SOLUBLE VITAMINS
CHAPTER OVERVIEW
Part three of the text, “The Vitamins and Minerals,” begins with a discussion of the fat-soluble
vitamins. A brief history of vitamins, storage of vitamins in the body, toxicity, preservation of vitamins in
foods, and their absorption is presented. Next, each vitamin, that is, vitamins A, D, E, and K, is introduced
individually to the learner with respect to their: 1) structure; 2) absorption, transport, and storage; 3)
functions; symptoms of deficiency and toxicity; 4) food sources; and 5) recommended intakes. Vitamins
are further compared to the action of the macronutrients discussed in previous chapters. An expert opinion
on “Vitamin E: An Exception to the Rule that Synthetic and Natural Forms of Vitamins are Identical”
supplements the chapter. Finally, The Nutrition Perspective asks and answers the question, “Vitamin
Supplements: Who Needs Them?”
CHAPTER OBJECTIVES
By the end of this chapter the student should be able to:
1.
Describe the absorption, storage, and risks of toxicity of the fat-soluble vitamins.
2.
List the functions of each fat-soluble vitamin.
3.
Identify food sources and state the recommended intake of each of the fat-soluble vitamins.
4.
Describe the signs and symptoms of fat-soluble vitamin deficiencies and toxicities.
5.
Describe the procedures used to assess nutritional status of fat-soluble vitamins.
6.
Identify the population group or groups at risk for fat-soluble vitamin deficiencies.
7.
Discuss those individuals most likely to need supplements and how to select a supplement.
LECTURE NOTES
I.
Vitamins: Vital Dietary Components
A. Introductory Information
1. Essential Organic Micronutrient (i.e., carbon-containing)
2. In General, Body Does Not Synthesize
3. Absence Can Cause Deficiency
4. Megadoses Can Be Harmful
5. Analog - chemical compound that differs slightly from another naturally occurring
compound
6. Natural versus synthetic (Is there a difference?)
B. Historical Perspective on the Vitamins
C. Storage of Vitamins in the Body
1. Fat Versus Water Soluble
a. Most water soluble vitamins are excreted and not stored
b. Fat soluble vitamins are not excreted (exceptions: vitamins K and B 12)
c. Signs and symptoms of a vitamin deficiency occur only when the vitamin is lacking
in the diet and body stores are essential exhausted
D. Vitamin Toxicity
1.
II.
Toxicities from Fat Soluble Vitamins (especially vitamin A and D supplements) are more
likely than Toxicity from Water Soluble Vitamins
2. Regular use of a “one-a-day” Type of Multivitamin/mineral Supplement is Unlikely to
Cause Toxic Effects in Nonpregnant Adults
E. Malabsorption of Vitamins
1. Can Lead to Deficiency States
2. Alcohol and certain intestinal diseases can also lead to deficiency states (cystic fibrosis,
Crohn’s disease, celiac disease)
F. Preservation of Vitamins in Food
1. Water soluble vitamins, especially thiamin, vitamin C, and folate, can be destroyed with
improper storage and excessive cooking
2. Heat, light, exposure to air, cooking in water, and alkalinity are factors that can destroy
vitamins
3. Refrigeration, cutting and cooking techniques, proper storage of canned vegetables are
important
4. Freezing is the best method to retain nutrients if the food is not eaten with a few days
G. Absorption of the Fat-Soluble Vitamins
1. Absorbed along with dietary fat (40%-90%)
2. Bile salts and lipoprotein lipase are involved in the packaging of fat soluble vitamins that
are delivered to target cells by way of chylomicrons and other lipoproteins
3. Role of the Liver
4. A disease interfering with fat absorption interferes with fat soluble vitamin absorption
Vitamin A
A. Structure and Nomenclature
B. Absorption, Transport, Storage, and Excretion of Vitamin A
1. Release of vitamin A from food requires bile, pancreatic enzymes, the intestinal tract, and
integration into micelles
2. Overall, absorption depends on the amount of fat in the diet
3. Both forms of vitamin A are transported via chylomicrons and released to the liver as
chylomicron remnants
4. Retinoids are stored in the liver; carotenoids are stored in the liver and adipose tissue
5. Not readily excreted; kidney disease increases risk of vitamin A toxicity if this route of
excretion is compromised
C. Cellular Retinoid-Binding Proteins
1. Retinoids are bound to specific retinoid-binding proteins in blood plasma, intercellular
spaces and within cells
2. Besides transport, these binding proteins protect vitamin from oxidation and enzymatic
reactions
D. Nuclear-Retinoid Receptors
1. Two main families
a. Retinoic receptor (RAR)
b. Retinoid X receptor (RXR)
2. Interact with retinoic acid and bind with specific sites on DNA, which allows for cell
differentiation
E. Functions of Vitamin A
1. Three active forms of vitamin A
a. Retinal
b. Retinal
c. Retinoic acid
2. Vision
a. Sensory Elements of the Retina
1. Rods
2. Cones
b. The Visual Pigment Rhodopsin is formed from 11-cis retinal and opsin
c. Visual Cycle
1. Light strikes retina of eye (bleaching process)
2. Rhodopsin structure altered so that nerve fibers carry visual signal to brain
3. Dark adaptation is the process by which rhodpsin concentration in the eye
increases in dark conditions
d. Sign of dietary deficiency: Night blindness
3. Cellular Growth and Differentiation
a. Fundamental function of retinoic acid is cell differentiation
b. Retinoic acid influences gene expression of mucus-forming cells
i. Lubricant needed for eyes to prevent Xerophthalmia
ii.. Skin lubricant to prevent follicular hyperkeratosis
iii. Vitamin A as retinoic acid affects growth and development
iv. Cell to cell communication
4. Immunity
a. Deficiency is associated with decreased resistance to infection
b. Contributes to a variety of immune processes
5. Carotenoid Actions
a. Appear to Function as Antioxidants
b. Acts as a source of vitamin A
c. Linked to a variety of health benefits
d. Clinical trials have not shown carotenoids to be responsible for any specific
reduction in disease risk
G. Vitamin A Deficiency
1. Xerophthalmia
2. Follicular hyperkeratosis
3. Possible Solutions
a. Find a suitable food to improve intake
i. Fortification of food with vitamin A is being explored as a possible solution to
widespread vitamin A deficiency in many developing countries
H. Cancer Prevention and Treatment
1. Studies Supporting the Benefits of Vitamin A and Beta-carotene
2. Reactive oxygen species
I. Cardiovascular Disease Prevention
1. Carotenoids may play a role
J. Eyesight
1. Macular degeneration—will carotenoids help?
K. Pharmacologic Use of Vitamin A
1.
Epithelial cells proliferation and differentiation are controlled by natural and synthetic
retinoids
2. Both systemic and topical agents are used to regulate the expression of skin growth
factors
a. 13-cis-retinoc acid (Accutane) – oral drug
b. Retin-A – (tretinoin) topical treatment of acne
c. Acitretin for severe cases of psoriasis; can cause toxic symptoms and birth defects if
used during pregnancy
L. Dietary Sources of Vitamin A and Carotenoids
1. Preformed Vitamin A
2. Provitamin A Carotenoids
3. Highest nutrient density for vitamin A (ug/kcal)

carrots, liver, spinach and other greens, sweet potatoes, winter squash, romaine
lettuce, broccoli, apricots
M. Retinal Activity Equivalents (RAE)
1. Current unit of measurement of vitamin A
2. Basically, 1 RAE = 1 ug of retinal
3. Conversion Values

Retinol activity equivalents (RAE); old system was IUs/day

1 microgram all-trans- retinal = 1 RAE

12 micrograms all- trans-beta-carotene = 1 RAE
 24 micrograms of other provitamin A carotenoids = 1 RAE
N. DRI for Vitamin A
1. Estimated Average Requirement
a. 625 ug RAE for men 19-70+ and 500 ug for women of the same age
b. See cover for others
O. North Americans at Risk for Vitamin A Deficiency
1. Those at risk
a. Preschool children who do not eat enough vegetables
b. Urban poor, the elderly, people with alcoholism or liver disease
c. Children and adults with severe fat malabsorption syndromes
P. Vitamin A Toxicity
1. Hypervitaminosis A
2. Kinds of vitamin A toxicity
a. Acute – GI upsets/nausea, headaches, dizziness, muscular uncoordination
b. Chronic – liver damage, hair loss, bone/muscle pain, loss of appetite, dry skin and
mucous membranes
c. Teratogenic – fetal malformations, spontaneous abortions
III. Vitamin D
A. Structure and Nomenclature
1. Prohormone
2. General Guidelines for Synthesis of Vitamin D via Sun Exposure
B. Vitamin D Formation in the Skin
1. Begins with 7 – dehydrocholesterol located in skin
2. UV light on skin opens ring to form vitamin D cholecalciferol
3. Cholecalciferol bound to a protein in blood and transported to the liver
C. Absorption and Formation of Vitamin D from Food
1. Following consumption of vitamin D containing food, 80% of vitamin D is incorporated
into micelles in small intestine, absorbed and transported to liver
D. Metabolism, Transport, and Storage of Vitamin D
1. Hydroxylation required for active vitamin D synthesis
a. Vitamin D precursor is hydroxylated on carbon 25, converting it to 25-OHvitamin D
b. Active form of vitamin D is produced in kidney; 1,25 (OH) 2 vitamin D
2. Parathyroid hormone regulates production of 1,25(OH) 2 vitamin D in kidney
3. Eventual excretion of vitamin D occurs in bile and small amount through urine
E. Functions of Vitamin D
1. Maintains serum calcium levels by mobilizing calcium and phosphorus from bone stores
during of calcium shortage
2. 1,25(OH)2 vitamin D induces stem cell monocytes to become mature osteoclasts, bone
degrading cells which release calcium into blood
3. Responsible for maintaining extracellular calcium and phosphorus concentrations in
supersaturated state
4. Effects proliferation and differentiation of skin cells
F. Rickets and Osteomalacia
1. Rickets
a. Definition
b. Signs of Rickets
i. enlarged head, joints, rib cage
ii. deformed pelvis
iii.
bowed legs
c. Those at Risk
2. Osteomalacia
a. Rickets in adults
b. Signs of Osteomalcia
i. fractures in hip, spine, and other bones
c. Those at Risk
G. Dietary Sources of Vitamin D
1. Few foods contain appreciable amounts of vitamin D
2. Most nutrient dense sources (ug/kcal)
a. fatty fish,
b. fortified milk
c. Some fortified cereals
3. Form in Plant Versus Animal Foods
H. Vitamin D Needs
1. DRI

Adequate Intake for vitamin D = 5 ug/day for people under age 51
Adequate Intake for vitamin D = 10 ug/day for people between ages 51 and 70
Adequate Intake for vitamin D = 15 ug/day for older Americans
Infants are born with supply of vitamin D to last 9 months
IV.
Breastfed infants should be regularly exposed to sunlight or be given a vitamin
D supplement
Infant formulas are fortified with vitamin D
2. North Americans at Risk for Vitamin D Deficiency
a. Elderly especially those living in northern climates or nursing homes
3. Vitamin D Resistance
a. Can be caused by lack of synthesis of 1,25(OH) 2-D in kidneys or inability of
1,25(OH)2-D to bind to nuclear receptors throughout body
4. Vitamin D Supplements
a. Usage
i. With low circulating concentration of 1,25(OH)2-D, 20 ug of vitamin D should
be taken each day until concentration reaches mid-normal range
ii. after that 10 ug/day form a multivitamin/mineral supplement should be
sufficient
b. Older people, especially those with osteoporosis, individuals with malabsorption
syndromes, liver failure, and kidney disease or failure are possible candidates
I. Pharmacologic Use of Vitamin D
1. Vitamin D analogs today are used as a safe, effective treatment in psoriasis
J. Vitamin D Toxicity
1. 5 times AI can be hazardous, especially during infancy to children
2. UL
3. Primary symptoms
a. over absorption of calcium with calcium deposits in kidneys, heart and blood vessels
b. weakness
c. loss of appetite
d. diarrhea
e. Severe vitamin D toxicity in infants causes mental retardation, changes in facial
characteristics, narrowing of pulmonary arteries and the aorta
Vitamin E
A. Structure and Nomenclature
1. Tocopherols
2. Tocotrienols
B. Absorption, Transport, Storage, and Excretion of Vitamin E
1. Absorption
a. Degree of absorption of vitamin E depends on total absorption of dietary fat
b. Absorption pattern follows other fat soluble vitamins
2. Transport and Storage
a. Chylomicrons and lipoproteins are necessary for transport to liver, adipose tissue and
skeletal muscle, where it can be stored
b. Associates itself with phospholipids in cell membrane
3. Excretion
a. Urine
b. Bile
C. Functions of Vitamin E
1. Antioxidant
a.
Cell membranes, which are subject to high risk of oxidation, are in lungs, brain, and
red blood cells
b. Stops Free Radical Chain Reactions
c. Free radicals
i. Group of electron seeking compounds found in cells and are highly reactive
molecules containing an unpaired electron
ii. Cause damage partially by setting off a chain reaction that can lead to lipid
peroxidation and destruction of cell membranes
2. Other Antioxidant Systems and Vitamin E
a. Carotenoids
b. Other Enzyme Systems convert oxidizing agents to less reactive compounds
i. Glutathione peroxidase catalyzes breakdown on peroxidized fatty acid
converting them to less harmful substances
o Activity of enzyme depends on adequate intake of selenium
o An adequate intake of selenium reduces need for vitamin E, but an
inadequate intake of selenium increases the need for vitamin E
ii. Superoxide dismutase react directly with reactive oxygen species or peroxides to
reduce their reactivity
o Various forms of superoxide dismutase contain zinc, copper, and
manganese
iii. Catalase also reacts directly with reactive oxygen species
3. Other Roles for Vitamin E
a. Protect carbon-carbon double bonds
b. Iron metabolism in the cell
c. Maintenance of nervous tissues and immune function
d. Inhibits protein kinase C activity
e. Enhances release of prostaglandins
D. Dietary Sources of Vitamin E
1. Most nutrient dense sources (mg/kcal)
a. plant oils
b. wheat germ
c. asparagus
d. peanuts
2. Products from plant oils, margarines, shortenings, salad dressings are good sources,
as are grain meals, nuts and seeds are also good sources of vitamin E
3. Animal fats have practically no vitamin E
E. Vitamin E Needs
1. Hemolysis of red blood
2. DRI
a. RDA for vitamin E is 15 mg for both men and women
b. RDA is set using mg-d-alpha-tocopherol
3. Natural Versus Synthetic
a. To determine number of mg of d-alpha-tocopherol from synthetic source,
multiply older IUs by 0.45
b. To determine number of mg of d-alpha-tocopherol from natural source, multiply IUs
by 0.67
c. Natural form has greater amount of active vitamin than synthetic form
d. Natural form is more expensive and has shorter shelf life
F. Medical Problems Associated with Vitamin E Deficiency
1. Hemolytic anemia
a. Definition
b. At Risk Groups
i. Preterm infants highly susceptible, since they are born with limited stores of
vitamin E, are inefficient at absorbing vitamin E from gut, and undergo
rapid growth with limited sources of the vitamin
2. Maldigestion of lipids and insufficient production of bile production can compromise
vitamin E status
3. Primary deficiency is peripheral neuropathy, which is rare in healthy humans
G. Vitamin E Toxicity
1 Upper Level
a Based on hemorrhagic effects in adults
b 1000 mg/day of any for of supplementary alpha tocopherol
c 1500 IU isolated from natural sources and 1100 IU from synthetic vitamin E
2. Individuals who are vitamin K deficient or taking anticoagulants are at risk for
hemorrhaging from megadoses of vitamin E
H. Questions that Remain About Vitamin E
1. Large-scale studies to assess more specifically vitamin E requirements for children
2. Better methods estimating intake of vitamin E
3. Tissue levels of the vitamin
4. Do large doses of vitamin E protect tissues against peroxidation , as they protect
LDL against oxidation?
5. Clinical trial to determine if vitamin E can reduce or prevent a whole range of
chronic diseases
I. Expert Opinion “Vitamin E: An exception to the rule that synthetic and natural forms of
vitamins are identical”
V. Vitamin K (Phylloquinones and Menaquinones)
A. Structure and Nomenclature
B. Absorption, Transport, Storage, and Excretion of Vitamin K
1. 80% taken up by enterocytes and incorporated into chylocmicorns
2. Menoquinones synthesized by bacteria in coon are absorbed but amount is unknown
3. Some vitamin K is stored in liver, some is inactivated, and some incorporated into
lipoproteins for transport throughout body
4. Mineral oil and other non-absorbable lipids interfere with vitamin K absorption
5. Most vitamin K excretion occurs via the bile, a small amount via urine
C. Functions of Vitamin K
1. Contributes to the synthesis of seven blood-clotting factors
2. Converted to an inactive form once it has acted and must be reactivated for its biological
action to persist
a. Anticoagulants strongly inhibit the reactivation process
3. Functions as a cofactor
a. For the enzyme that catalyzes conversion of glutamate to gamma- carboxyglutamate
b. For synthesis of osteocalcin and matrix Gla protein
c.
Deficiency most likely to occur when individual takes antibiotics or has impaired fat
absorption
D. Dietary Sources of Vitamin K
1. Most nutrient dense source of vitamin K (mg/kcal) are liver, green leafy vegetables,
broccoli, peas, and green beans
2. Vitamin K is abundant in diet and quite resistant to cooling losses
E. Vitamin K Needs
1. RDI
a. Adequate Intake for women ages 19-70+ is 90 ug/day
b. Adequate Intake for men ages 19-70+ is 120 ug/day
2. Megadoses of vitamins A and E may pose a risk to vitamin K status
3. Vitamin k deficiency can occur in newborns because they lack GI bacteria to synthesis v
vitamin K
a. Within 6hours of birth, vitamin K routinely given IM
4. Toxicity is unlikely because vitamin K is readily excreted
F. Nutrition Perspective: Nutrient Supplements: Who Needs Them?
1. Dietary Supplement Health and Education Act of 1994
a. a supplement is a product intended to supplement the diet and contains one or more
of the following dietary ingredients
i. Vitamin, Mineral, herb or another botanical
ii. An amino acid, a dietary substance to supplement the diet which could be an
extract or a combination of the first four ingredients noted above
2. $13 billion business)
3. Supplement makers can make broad claims about their product under the “structure or
function” provision of the law
4. Products cannot claim to prevent, treat or cure a disease
5. People most likely to need supplements
a.
b.
c.
d.
e.
6.
Women in child-bearing years may need extra synthetic folate
Women with excessive bleeding during menstruation may need extra iron
Women who are pregnant or breastfeeding may need extra iron, folate and calcium
Strict Vegans may need extra calcium, zinc, iron, and vitamin B 12
People with low energy intakes, some women and many older people, may need a
range of vitamins and minerals
f. Newborns need a single dose of vitamin K
g. People with limited milk intake and sunlight exposure may need extra vitamin D
h. People with lactose intolerance or allergies to dairy products may need extra calcium
i. People with very low fat diets may need extra vitamin E
j. Individuals with certain medical conditions
Which supplement to choose?
a. If you choose to take a vitamin/mineral supplement choose:
i. A national brand from a supermarket or pharmacy
ii. One that contains no more than the Upper Level of each vitamin and mineral
iii. One that is low or free of iron for men
iv. One that is fortified with vitamin B12 for older people
b. Avoid superfluous ingredients
ACTIVITIES, EXERCISES, AND ASSIGNMENTS (Additional Activities in
Text)
1.
Assign students to conduct a library search of current literature to determine the magnitude of
vitamin A deficiency and report on techniques that have been successfully used to prevent vitaminA deficiency blindness in children.
2.
Assign students to select food or vitamin supplement labels and convert IUs into retinol equivalents
of vitamin A, IUs into milligrams of vitamin D, and 1U of vitamin E to milligrams.
3.
Because many foods are fortified with vitamins A and D, assign students to check a variety of labels
to determine which foods are fortified with these vitamins, such as cereals, cereal products, milk,
dairy products, margarine.
4.
Request students to consult printouts from previous FoodWorks computer assignments to determine
the level of vitamins A, D, and E and report on the best sources of these vitamins in their menu.
5.
Research the biochemical pathways and mechanisms in which Vitamin E, Selenium, glutathione
peroxidase and catalase act as antioxidants. Do these have food sources in common? If so, list these
foods.
ANNOTATED REFERENCES AND READINGS (Annotated References in
Text)
1.
Vitamin and Nutritional Supplements: Nutrition, Annual Editions 98/99, Article 48, pp.181-195,
1997.
2.
Halliwell, B: Antioxidants in Human Health and Disease, Ann. Rev. Nutr., 16:33-50, 1996.
3.
Norman, AW (1996): Vitamin D. In Ziegler EE and Filer LJ (eds.), Present Knowledge in Nutrition,
7th ed., International Life Sciences Institute, Washington, DC pp. 120-129.
4.
Canfield, LM, et. al.: Carotenoids in Human Health, Ann NY Acad Sci, 691:1-300, 1995.
5.
Olson, JA: Vitamin A, retinoids and carotenoids. In Shils ME, Olson JA, Shike M (eds), Modern
Nutrition in Health and Disease, 8th ed., Lea & Fibiger, Philadelphia, pp. 287-307, 1994.
6.
Gopalan, C: Keratomalacia and nutritional blindness in: The contribution of nutrition research to the
control of undernutrition: the Indian experience, Annual Review of Nutrition 12:6, 1992.
7.
Hill, DL and CJ Grubbs: Retinoids and cancer prevention, Annual Review of Nutrition 12:161,
1992.
8.
Byers, T and G Perry: Dietary carotenes, vitamin D, and vitamin E as protective antioxidants in
human cancers, Annual Review of Nutrition 12:139, 1992.
9.
Suttie, JW: Vitamin K and human nutrition, Journal of the American Dietetic Association 92:585,
1992.
10.
Smigel, K: Vitamin E moves on stage in cancer prevention studies, Journal of the National Cancer
Institute 84:996, 1992.
11.
Slater, TF and G Block, eds.: Antioxidant vitamins and beta-carotene in disease prevention.
Proceedings of a conference held in London, UK, The American Journal of Clinical Nutrition
53:(January Supplement) 189S, 1990.
MEDIA RESOURCES
Slides:
1.
Foods and Immunity: Complete Slide Presentation. NCES, 1904 East 123rd Street, Olathe, KS
66061-5886.
2.
Nutrition: Vitamins and Minerals. Milner-Fenwick Corp., Timonium, MD
Films:
1.
Vitamins, What Do They Do? Alfred Higgins Productions, Los Angeles, CA.
Filmstrips:
1.
Fat-Soluble vitamins. Educational Audio Visual, Inc., 17 Marble Avenue, Pleasantville, NY 10570.
Video:
Vitamins I, II (fat-soluble vitamins). Audio-Visual Department, Pennsylvania State University, University
Park, PA 16803.