Transcript The Fat-Soluble Vitamins

The Fat-Soluble Vitamins
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Vitamin A
Vitamin D
Vitamin E
Vitamin K
Dr. Latifah Al-Oboudi 2012
Vitamins: Essential Dietary
Components
• Vitamins are essential, organic compounds
needed for important metabolic reactions in
the body.
• They are not a source of energy. Instead, they
promote many energy-yielding and other
reactions in the body, thereby aiding in the
growth, development, and maintenance of
various body tissues.
Dr. Latifah Al-Oboudi 2012
•Vitamins cannot be synthesized in the body at all or
are synthesized in insufficient amounts.
•Vitamins A, D, E, and K are fat soluble, whereas the Bvitamins and vitamin C are water soluble.
Dr. Latifah Al-Oboudi 2012
Absorption of vitamins
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Fat-soluble vitamins are
absorbed along with dietary
fat. Thus adequate absorption
depends on the efficient use
of bile and pancreatic lipase in
the small intestine to digest
dietary fat and the adequate
absorptive capacity of the
intestinal mucosa.
• Under optimal condition,
about 40 to 90% of the fatsoluble vitamins are absorbed
when they are consumed in
recommended amounts.
Dr. Latifah Al-Oboudi 2012
Malabsorption of vitamins
• Fat malabsorption (resulting from GI tract and
pancreatic disease) may cause poor
absorption of fat-soluble vitamins.
• In disease states that limit fat digestion, fatsoluble vitamin absorption may be
compromised, thereby increasing the risk of
deficiency in these individuals.
Dr. Latifah Al-Oboudi 2012
Transport of vitamins
• They travel by way of the lymphatic system
into general circulation, carried by
chylomicrons.
Dr. Latifah Al-Oboudi 2012
Vitamin Toxicity
• Fat –soluble vitamins are excreted less readily
from the body than water-soluble vitamins
and thus pose a potential threat for toxicity,
especially of vitamins A and D.
• Toxicities of these fat- soluble vitamins
generally occur with high doses of
supplements, rather than from foods
Dr. Latifah Al-Oboudi 2012
Vitamin A
• Vitamin A contributes to the maintenance of
vision, the normal development of cells
(especially mucous-forming cells), and
immune function.
Dr. Latifah Al-Oboudi 2012
Vitamin A
• Vitamin A refers to the preformed retinoids
and provitamin A carotenoids that can be
converted to vitamin A activity.
• Retinoids is a collective term for the
biologically active forms of vitamin A because,
unlike carotenoids, they do not need to be
converted to become biologically active.
Dr. Latifah Al-Oboudi 2012
Vitamin A
• Retinoids exist in 3 forms: retinal(an aldehyde), retinol(an
alcohol), and retinoic acid.
• Carotenoids are yellow-orange pigmented materials in
vegetables and fruits, some of which are provitamins--that is, they can be converted into vitamin A.
• A plant derivative, known as beta-carotene, along with 2
other carotenoids(alpha-carotene and beta- cryptoxanthin),
yields vitamin A after metabolism by the small intestine or
liver.
Dr. Latifah Al-Oboudi 2012
Interconversions of beta-carotene and various retinoids. Notice that the synthesis of
retinoic acid is a “dead end” in metabolic terms.
Dr. Latifah Al-Oboudi 2012
Dr. Latifah Al-Oboudi 2012
Vitamin A in Foods
• Retinoids (preformed vitamin A) are found in
foods of animal origin, such as liver, fish, fish
oils, fortified milk and eggs.
• A carotenoids are found mainly in dark green
and yellow-orange vegetables and fruits, such
as carrots, spinach and other greens, winter
squash, sweet potatoes, broccoli, mangoes,
cantaloupe, peaches, and apricots.
Dr. Latifah Al-Oboudi 2012
Food sources of vitamin A
Dr. Latifah Al-Oboudi 2012
• At one time the amounts of vitamin A were
expressed in International Units (IUs). Today,
there are more sensitive means for measuring
nutrients. Consequently, milligram (1/1000 of
a gram) and microgram (1/1,000,000 of a
gram) measurements have generally replaced
IUs as the units of measure. However, some
food and vitamin supplement labels may still
display the older IU value.
• Dietary vitamin A activity is currently
expressed in Retinol Activity Equivalents(RAE)
Dr. Latifah Al-Oboudi 2012
Dr. Latifah Al-Oboudi 2012
Vitamin A Needs
• The RDA for vitamin A is 900 µg Retinol
Activity Equivalents(RAE) per day for adult
men and 700 µg RAE per day for adult women.
Dr. Latifah Al-Oboudi 2012
Absorption, Transport, Storage, and
Excretion of Vitamin A
• Up to 90% of retinol is absorbed into the cells
of the small intestine.
• After absorption, a fatty acid is attached to
retinol to form a new retinyl ester. These
retinyl esters are packaged into chylomicrons
before entering the lymphatic circulation.
Dr. Latifah Al-Oboudi 2012
Absorption, Transport, Storage, and
Excretion of Vitamin A
• The provitamin A carotenoids can be
enzymatically split within the intestinal cells
or liver cells to form retinal or, to lesser
extent, retinoic acid.
• The carotenoid absorption is much lower than
that of retinol.
• After being absorbed in the small intestine ,
carotenoids can be cleaved to yield retinal,
which is then converted to retinol.
Dr. Latifah Al-Oboudi 2012
Absorption, Transport, Storage, and
Excretion of Vitamin A
• The chylomicrons deliver vitamin A to tissue
for storage or cellular use.
• Storage: Over 90% of the body’s vitamin A
stores are found in the liver, with small
amounts in adipose tissue, kidneys, bone
marrow, testicles, and eyes. Normally, the liver
stores enough vitamin A to last for several
months to protect against vitamin A
deficiency.
Dr. Latifah Al-Oboudi 2012
Excretion of Vitamin A
• Although vitamin A is not readily excreted by
the body, some is lost in the urine.
• Kidney disease increases the risk of vitamin A
toxicity because this urinary route of excretion
is compromised.
Dr. Latifah Al-Oboudi 2012
Functions of Vitamin A ( Retinoids)
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Growth and Development.
Cell Differentiation.
Vision.
Immune Function.
Dr. Latifah Al-Oboudi 2012
Vitamin A deficiency Diseases
• Conjunctiva:
• Xerophthalmia:
Dr. Latifah Al-Oboudi 2012
Vitamin A Toxicity
• Preformed vitamin A can be quite toxic when
taken at doses 2 to 4 times or more the RDA.
• Use of vitamin A supplements is especially
dangerous during pregnancy because it can lead to
fetal malformations.
Dr. Latifah Al-Oboudi 2012
Vitamin A Toxicity
• Consuming the right amount of vitamin A is critical to overall health. Avery
low (deficient) or very high (toxic)vitamin A intake (as retinoids) can
produce harmful symptoms and can even lead to death.
Dr. Latifah Al-Oboudi 2012
Golden rice was genetically engineered to synthesize beta-carotene. This rice was
developed for use as a fortified food in areas of the world that have limited access to
vitamin A-rich foods.
Dr. Latifah Al-Oboudi 2012
Dr. Latifah Al-Oboudi 2012
Vitamin D
• In presence of sunlight, skin cell synthesize a
sufficient supply of vitamin D from a derivative
of cholesterol.
• Dietary source is not required if synthesis is
adequate to meet needs, the vitamin is more
correctly classified as a “conditional” vitamin
or prohormone (a precursor of an active
hormone).
Dr. Latifah Al-Oboudi 2012
Vitamin D
• In the absence of UV light exposure, an adequate
dietary intake of vitamin D is essential to prevent the
deficiency diseases rickets and osteomalacia and to
provide for cellular needs.
• After exposure to the sun, humans produce vitamin D₃
(cholecalciferol) from a derivative of cholesterol.
• The liver and kidneys each add a hydroxyl group(-OH)
to this to yield the active form of vitamin D ( 1,25
dihydroxy D₃, or calcitriol).
Dr. Latifah Al-Oboudi 2012
Vitamin D₂ in foods
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The best food sources of vitamin D are:
Fatty fish (e.g. sardines, mackerel, and salmon).
Cod liver oil.
Fortified milk.
Some fortified breakfast cereals.
Although eggs, butter, liver, and a few brands of
margarine contain some vitamin D, large servings
must be eaten to obtain an appreciable amount
of the vitamin. Thus, these foods are not
considered a significant source.
Dr. Latifah Al-Oboudi 2012
Cod liver oil was a common supplements for children in the US until 1933, when milk
was first fortified with vitamin D
Dr. Latifah Al-Oboudi 2012
Vitamin D₂ in foods
• Most fortified foods and supplements
containing vitamin D are in the form of
ergocalciferol, or vitamin D₂, the same form
found naturally in foods.
• Ergocalciferol has vitamin D activity in
humans, but in lesser amounts than provided
by cholecalciferol (vitamin D₃).
Dr. Latifah Al-Oboudi 2012
Food sources of vitamin D
Dr. Latifah Al-Oboudi 2012
Dr. Latifah Al-Oboudi 2012
Vitamin D₃ Formation in the Skin
• The synthesis of vitamin D₃ begins with a compound
called 7-dehydrocholesterol, a precursor of cholesterol
synthesis located in the skin.
• 1 ring on the molecule undergoes a chemical
transformation, forming the more stable vitamin D₃
(cholecalciferol).
• This change allows vitamin D₃ to enter the bloodstream
for transport to the liver and kidneys, where it
undergoes hydroxylation (the addition of -OH) and
subsequent conversion to its bioactive form 1,25
dihydroxy D₃ (calcitriol).
Dr. Latifah Al-Oboudi 2012
Vitamin D₃ Formation in the Skin
• For many individuals, sun exposure provides
80 to 100% of the vitamin D₃ required by the
body.
• The amount of sun exposure needed ,
however, depend on the time of day, the
geographic location, the season of the year,
one’s age, one’s skin color, and the use of
sunscreen.
Dr. Latifah Al-Oboudi 2012
• The production of vitamin D₃ in the skin
decreases by about 70% when one reaches
the age of 70. older people are advised to get
small amounts of sun exposure, or to take
vitamin D supplements to prevent deficiency.
• The large amount of melanin (skin pigment) in
dark-skinned individuals may block UV light
and prevent adequate vitamin D₃ synthesis.
Dr. Latifah Al-Oboudi 2012
• Scientists recommend that people expose their
hands, face, and arms to UV light at least 2 or 3
times a week for 10 to 15 minutes.
• Individuals with dark skin may need sun exposure
of 3o minutes or more (or vitamin D
supplementation).
• People who do not receive enough UV light
exposure to synthesize adequate amounts of
vitamin D₃ should make certain that they have
adequate sources of vitamin D in their diets.
Dr. Latifah Al-Oboudi 2012
Vitamin D Needs
• The adequate intake for vitamin D is 5µg/day (200 IU/day)
for people under age 51, 10µg/day (400 IU/ day) for people
between 51 and 70, and 15µg/day (600 IU/ day) for older
adults.
• Older adults may need 20 to 25µg/day (800 to 1000 IU/
day) from a combination of vitamin D-fortified foods and a
supplement to decrease the risk of bone loss and other
chronic diseases.
• The daily value used on food and supplements labels is 10
µg.
• Breastfed infants recommended to be given a vitamin D
supplement of 5 µg/day (200 IU) until they are weaned to
infant foods fortified with, or rich in, vitamin D .
Dr. Latifah Al-Oboudi 2012
Absorption, Transport, Storage, and
Excretion of Vitamin D
• About 80% of vitamin D₂ is incorporated
(along with other dietary fats) into micelles in
the small intestine, absorbed, and transported
to the liver by chylomicrons through the
lymphatic system.
Dr. Latifah Al-Oboudi 2012
Whether synthesized in the skin or obtained from dietary sources, vitamin D
ultimately function as a hormone: 1,25(OH)₂ vitamin D₃ (calcitriol)
Dr. Latifah Al-Oboudi 2012
Function of Vitamin D
• Vitamin D has hormone like functions, which
help regulate the body’s concentration of
calcium and phosphorus
Dr. Latifah Al-Oboudi 2012
Figure 12-13 The active vitamin D
Hormone– 1,25 (OH)₂ vitamin D₃ --and
parathyroid hormone interact to control
blood calcium concentration. Low blood
calcium is a trigger for the following
actions, all of which raise blood calcium
levels.
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Parathyroid hormone (PTH) and
1,25(OH)₂ vitamin D₃ mobilize calcium from
the bone.
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PTH also
a. Reduces calcium excretion by the
kidneys.
b. stimulates kindly synthesis of
1,25(OH)₂ vitamin D₃.
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1,25(OH)₂ vitamin D₃ stimulates
intestinal calcium absorption.
Conversely, when calcium levels in the
blood become too high, the hormone
calcitonin responds by promoting calcium
disposition in the bone (see chapter 14)/.
Dr. Latifah Al-Oboudi 2012
Function of Vitamin D
• Vitamin D promotes increased intestinal
absorption of calcium and phosphorus from
foods to maintain blood levels of these minerals.
This makes calcium and phosphorus available for
body cells and for incorporation into bones when
there is more than needed for basic functions.
Dr. Latifah Al-Oboudi 2012
Function of Vitamin D
• When blood levels of calcium and phosphorus start to
fall, vitamin D (with PTH from the parathyroid gland) can
release calcium and phosphorus from bone into the
blood to restore blood levels of these minerals.
• This action can eventually weaken the bones if it
continues for a prolonged period of time, it helps provide
the calcium and phosphorus needed for many basic life
functions. If the bones did not supply calcium and
phosphorus for these functions, a person could quickly
have serious, even fatal, health consequences. Thus,
vitamin D preserves these important functions even if
dietary intakes of these minerals are inadequate.
Dr. Latifah Al-Oboudi 2012
Function of Vitamin D
• Vitamin D has important functions beyond its
role in maintaining calcium and phosphorus
homeostasis and bone health.
• Vitamin D also is involved in immune function
and cellular metabolism.
Dr. Latifah Al-Oboudi 2012
Function of Vitamin D
• Vitamin D also may be involved in cell cycle
regulation.
• Additionally, vitamin D may decrease the risk
of certain types of infections and autoimmune
diseases, such as multiple sclerosis, through
its action in the immune system and offer
protection against diabetes, hypertension, and
certain cancers.
Dr. Latifah Al-Oboudi 2012
Vitamin D Deficiency Diseases
• Vitamin D deficiency results in harmful
changes in bone, a condition known as rickets
in children and osteomalacia in adults.
Dr. Latifah Al-Oboudi 2012
The bone deformities and bowed legs of rickets,
a vitamin D deficiency disease in children.
Dr. Latifah Al-Oboudi 2012
Vitamin D Toxicity
• Vitamin D toxicity can occur from excessive
vitamin D supplementation, causing the
deposition of calcium in the kidneys, heart,
and lungs.
Dr. Latifah Al-Oboudi 2012
Vitamin E
• The importance of vitamin E was first noted in
1922 in rats.
• Vitamin E was not fully recognized as an essential
nutrient in humans until the mid-1960s.
• The first RDA for vitamin E was established in
1968.
• Vitamin E is a family of 8 naturally occurring
compounds- 4 tocopherols ( alpha, beta, gamma,
delta) and 4 tocotrienols (alpha, beta, gamma,
delta)—with widely varying degrees of biological
activity.
Dr. Latifah Al-Oboudi 2012
Vitamin E
• The most active form of the vitamin E is alphatocopherol.
• This is the form found in some foods and in
varying amounts in vitamin supplements.
• Gamma-tocopherol is a potentially beneficial
form of vitamin E found in many vegetable
oils. It does not have as much biological
activity as alpha-tocopherol.
Dr. Latifah Al-Oboudi 2012
Vitamin E in foods
• Vitamin E is plentiful in plant
oils(e.g., cottonseed, canola,
safflower, and sunflower
oils), wheat germ, asparagus,
almonds, peanuts, and
sunflower seeds.
• Products made from the
plant oils—margarine,
shortenings, and salad
dressings– also are good
sources.
Dr. Latifah Al-Oboudi 2012
Food sources of vitamin E
Dr. Latifah Al-Oboudi 2012
Vitamin E in foods
• Animal fats and dairy products contain little
vitamin E.
• The vitamin E content of a food depends on
harvesting, processing, storage, and cooking
because vitamin E is highly susceptible to
destruction by oxygen, metals, light, and
deep-fat frying. Thus, foods that are highly
processed and/or deep-fried are usually poor
sources of vitamin E.
Dr. Latifah Al-Oboudi 2012
Vitamin E needs
• The RDA for vitamin E is 15 mg/day of alphatocopherol for both men and women.
• The 15-mg allotment is equivalent to 22 IU of a
natural source and 33 IU of a synthetic source of
vitamin E .
• Adults consume, on average, only two-thirds of
the RDA for vitamin E each day.
Dr. Latifah Al-Oboudi 2012
Absorption, Transport, Storage, and
Excretion of Vitamin E
• Absorption can vary from 20 to 70% of dietary
intake. Vitamin E must be incorporated into
micelles in the small intestine, a process
dependent on bile and pancreatic enzymes.
• Once taken up by the intestinal cells, vitamin E
is incorporated into chylomicrons for transport
by the lymph and eventually the blood.
Dr. Latifah Al-Oboudi 2012
Absorption, Transport, Storage, and
Excretion of Vitamin E
• As chylomicrons are broken down, most of the
vitamin E is carried to the liver as chylomicron
remnants. A small amount is carried directly to
other tissues.
• The liver repackages the vitamin E from the
chylomicron remnants with other lipoproteins
(VLDL, LDL, and HDL) for delivery to body tissues.
• Vitamin E carried by these lipoproteins.
• Vitamin E does not accumulate in the liver;
instead, most of the vitamin E in the body is
localized in adipose tissue.
Dr. Latifah Al-Oboudi 2012
Excretion of Vitamin E
• Vitamin E can be excreted via the bile, urine,
and skin.
• However, because vitamin E absorption is
often low, most vitamin E is excreted via the
small amount of bile that exits the body in the
feces.
Dr. Latifah Al-Oboudi 2012
Function of Vitamin E
• Vitamin E is an antioxidant that stops chain
reactions caused by free radicals that can
potentially damage cells. Vitamin E acts
primarily in lipid-rich areas of the body,
where free radicals can initiate a chain of
reactions known as peroxidation.
Dr. Latifah Al-Oboudi 2012
Function of Vitamin E
• Lipid peroxidation reactions break apart fatty
acids and create free radicals called lipid
peroxyl radicals (also called reactive oxygen
species because they contain oxygen radicals).
• The chain of reactions continues to break
apart fatty acids until 2 free radicals pair and
stabilize each other. However, many lipid
peroxyl radicals may be produced through
these reactions before stabilization occurs.
Dr. Latifah Al-Oboudi 2012
Function of Vitamin E
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Vitamin E is one of the most effective
mechanisms for stopping lipid peroxidation
chain reaction in the body. By donating
hydrogen to lipid radicals, vitamin E stops the
chain of oxidation reaction, which protects the
lipids in the body. For example, recall that cell
membranes are composed of a phospholipid
bilayer
Dr. Latifah Al-Oboudi 2012
Fat-soluble vitamin E can donate an electron to stop free radical chain
reaction. If not interrupted, these reactions cause extensive damage to
cell membranes
Dr. Latifah Al-Oboudi 2012
Function of Vitamin E
• To vitamin E, the body has various other
antioxidant compounds, such as glutathione
peroxidase, catalase, and superoxide dismutase,
to protect against oxidative damage.
Dr. Latifah Al-Oboudi 2012
The body does not rely solely on vitamin E for antioxidant protection. Such
protection is a team effort, utilizing a number of nutrients, metabolites, and
enzyme systems.
Dr. Latifah Al-Oboudi 2012
Vitamin E Deficiency
• Overt vitamin E deficiency is rare in humans.
• Vitamin E deficiency is characterized by the
premature breakdown of red blood
cells(hemolysis) and the development of
hemolytic anemia.
• Vitamin E deficiency also can impair immune
function and cause neurological changes in
the spinal cord and peripheral nervous
system.
Dr. Latifah Al-Oboudi 2012
Vitamin E Toxicity
• Toxicity from megadose therapy inhibits
vitamin K activity and, in turn, increases the
risk of hemorrhage.
Dr. Latifah Al-Oboudi 2012
Vitamin K
• The discovery of vitamin K centered on its role
in blood clotting.
Dr. Latifah Al-Oboudi 2012
Vitamin K
• Vitamin K contributes to the body’s bloodclotting ability by facilitating the conversion of
precursor proteins, such as prothrombin, to
active clotting factors that promote blood
coagulation.
Dr. Latifah Al-Oboudi 2012
Vitamin K Sources
• About 10% of the vitamin K absorbed each day
comes from bacterial synthesis in the colon.
• The remainder comes from dietary sources,
green leafy vegetables (e.g., Kale, turnip greens,
parsley, salad greens, cabbage, and spinach),
broccoli, peas, and green beans are the best
sources.
• Vegetable oils, such as soy and canola, also are
good sources.
• Vitamin K can be destroyed by exposure to light.
Dr. Latifah Al-Oboudi 2012
Food sources of vitamin K
Dr. Latifah Al-Oboudi 2012
Vitamin K Needs
• For women, the adequate intake for vitamin K
is 90µg/day; for men, it is 120µg/day.
• The daily value for vitamin K is 80µg/day.
Dr. Latifah Al-Oboudi 2012
Absorption, Transport, Storage, and
Excretion of Vitamin K
• Approximately 80% of dietary vitamin K as
phylloquinone and menaquinone is taken up by
the small intestine and incorporated into
chylomicrons. This process requires bile and
pancreatic enzymes.
• The menquinones synthesized by bacteria in the
colon also are absorbed, but provide only 10% of
the vitamin K we need.
• Vitamin K can be incorporated into the
lipoproteins VLDL and LDL for transport
throughout the body or for storage in the liver.
Dr. Latifah Al-Oboudi 2012
Excretion of Vitamin K
• Most vitamin K excretion occurs via the bile
that passes out of the body in the feces, with
a small amount of excretion via the urine.
Dr. Latifah Al-Oboudi 2012
Function of Vitamin K
• Vitamin K is needed for the synthesis of bloodclotting factors by the liver and the conversion
of preprothrombin to the active blood-clotting
factor called prothrombin.
Dr. Latifah Al-Oboudi 2012
Forming a blood clot requires the participation of vitamin K in both the intrinsic
and extrinsic blood-clotting pathways. Vitamin K specifically imparts calciumbinding capacity to the proteins in these pathways, as in the conversion of
preprothrombin to prothrombin, an active clotting factor.
Dr. Latifah Al-Oboudi 2012
Function of Vitamin K
• Vitamin K also may play a role in bone
metabolism.
• Vitamin K also may help protect the body
from inflammation, thereby providing
protection against cardiovascular disease and
osteoporosis.
Dr. Latifah Al-Oboudi 2012
Vitamin K deficiency
• A deficiency of vitamin K is rare, but it can
occur with prolonged use of antibiotics that
disrupt vitamin K synthesis or with impaired
fat absorption.
• Vitamin K deficiency also can occur in
newborns. Newborn infants are given vitamin
K injections within 6 hours of delivery to
prevent this possible vitamin K deficiency.
Dr. Latifah Al-Oboudi 2012
Vitamin K Toxicity
• To date, no upper level has been set for
vitamin K.
• Although vitamin K can be stored in the liver
and bone, it is more readily excreted than
other fat-soluble vitamins.
• Can cause hemolytic anemia.
Dr. Latifah Al-Oboudi 2012
Dr. Latifah Al-Oboudi 2012
Dietary supplements: Healthful
or Harmful?
Dr. Latifah Al-Oboudi 2012
Which food provide very little vitamin A?
a. Mango
b. Spinach
c. Banana
d. Liver
Dr. Latifah Al-Oboudi 2012
Vitamin D deficiency in children results in a condition
called-------a. osteomalacia
b. Berberi
c. Rickets
d. xerophthalmia
Dr. Latifah Al-Oboudi 2012
Which vitamin aids in blood clotting?
a. Vitamin A
b. Vitamin D
c. Vitamin E
d. Vitamin K
Dr. Latifah Al-Oboudi 2012