Fat soluble Vitamins Flashcards
How does vitamin K specifically participate in the formation of clotting factors?
y function as co-factor of the carboxylase
enzyme in the synthesis of blood-clotting factors;
in the conversion of pre-prothrombin to
prothrombin in the liver
How does Warfarin ( blood thinning medication) interfere with vitamin K activity?
The medication Warfarin inhibits the enzyme enzyme
epoxide reductase which reduces oxidised
vitamin
Why is a high dose of vitamin E contradicted when someone is taking Warfarin?
?
What does it mean that the RDI for vitamin A is expressed in RE?
RDI: Vitamin A as retinol equivalent (RE)*
. How does vitamin E specifically act as an antioxidant? What is its fate after that?
Antioxidant activity: scavenging activity on lipid-derived peroxyl radicals in lipid bilayer. Retinoids do not donate hydrogen atoms, but rather act as a trap for lipoperoxyl radicals + regenerating of vitamins E and C.
What is the active form of vitamin A?
Retinoids Exist in 3 forms that can be interconverted: • Retinol (an alcohol) or retinyl esther (retinol bound to a fatty acid) • Retinal (an aldehyde) • Retinoic acid
Formation of active Vitamin D,
Ultraviolet light converts 7-dehydrocholesterol to vitamin D (cholecalciferol) in the skin.
Dietry vitamin D is absorbed with dietry fat in the intestine
Vitamin D from both dietary sources and syntheisis in the skin is bound to carrier protiens in the bloodstream and transported to liver.
Vitamin D in food or supliments is converted in the liver to 25-OH vitamin D
Vitamin D is converted in the kidney to 1,25(OH)2 VItamin D
Is the yellowing of the palms of your hands when consuming a lot of carrot juice a sign
of vitamin A toxicity? Why?
???
Which fat soluble vitamins (FSV) are stored in the body, and where?
Vitamin A
> 90% retinoids stores found in stellate cells of the liver, as retinyl esters (enough to
last several months), small amounts in adipose tissue, kidney, bone marrow, testicles,
eyes. Some stores of carotenoids in adipose tissue, cell membrane, in the eye
(lutein, zeaxanthin, beta carotene
vitamin D • In adipose tissue, liver, kidney
VItamin E adipose tissue
VItamin K Minimal, some in the liver. Recycled rapidly by the K-epoxide cycle for
optimal re-use
Function of VItamin D
Regulation of renin (blood pressure regulation), insulin, parathyroid hormone
secretion
• Gene expression signal for cell differentiation
• Regulation of immune function
• Protection against diabetes type 2, cancer, dementia (ongoing
investigations)
How does vitamin D specifically contribute to calcium homeostasis?
Vitamin D regulates calcium homeostasis by promotion of calcium absorption in the intestine, by reabsorption of calcium by the kidney, and by mobilization of calcium from the bone. 1,25(OH)2D through a negative feedback loop regulates the synthesis of PTH and of CYP27B1 (a) [4–6, 10].
2.Which vitamin is more potent in its natural form compared to synthetic form? Why?
Vitamin E
Why are International Units (IU) used for vitamins A, D and E?
The goal of the IU is to be able to compare these, so that different forms or preparations with the same biological effect will contain the same number of IUs.
Vitamin D deficiency
Deficiency - In children: Ricket's (bowed legs). Ricket’s is linked to vitamin D deficiency since 1918 - In adults: osteomalacia = soft bones • Deficiencies are related to: - season - location - ageing skin, always covered skin - chronic liver and kidney disease (Why?) - dark skin - intestinal disease (malabsorption issues, e.g. Crohn’s disease)
VItamin D toxcicity
Toxicity
- Does not occur from sunlight or dietary sources
- Occurs with supplementation overuse
- UL (80 µg or 3200IU) based on studies assessing effect
of vitamin D on blood calcium levels
- Above UL: can cause over absorption of calcium
and thus hypercalcaemia, calcium deposit in kidney,
joints, blood vessels, heart
- Vitamin D excess can also lead to bone
demineralisation (via too much bone resorption) =>
review diagram on role of vitamin D on bone calcium),
and can be fatal in chronic excess
VITAMIN E
DIGESTION, ABSORPTION, TRANSPORT AND EXCRETION
Absorption
- Absorption depends on presence of dietary fat and amount consumed
- 20-70% of dietary intake is usually absorbed
Transport
- Micelles to enterocytes: dependent on bile and pancreatic lipase
- Chylomicrons, through lymphatic system and to the liver (with some tissue delivery)
- Transported from liver via lipoproteins (VLDL, LDL, HDL) to tissues
Storage
- Stored in adipose tissue (90%) not in the liver
Excretion
- Bile, urine and skin
Vitamin E functions
Main function as antioxidant: as a peroxyl radical
scavenger (in membrane phospholipids and plasma
lipoproteins e.g. LDL).
Free radicals have 1000 fold greater reactivity with vitamin E
than with PUFA
- The phenolic hydroxyl group of tocopherol reacts with an
organic peroxyl radical to form an organic hydroperoxide and
the tocopheroxyl radical
- The tocopheroxyl radical must be reduced by other
antioxidants to tocopherol, or reacts with another tocopheroxyl
radical to form non-reactive products (tocopherol dimers), or
undergoes further oxidation to tocopheryl quinone (an anticoagulant –see later), or can act as a prooxidant and oxidize
other lipids
VItamin E defficiency
Deficiency
- Hemolytic anemia: premature hemolysis of red blood cells
- Impaired immune function, neuropathy, retinal damage
- Oxidative stress related and unspecific
- Reasons: malabsorption disease, genetic defects of transporters, and smoking
increase requirements of alpha tocopherol
VItamin E toxicity
Toxicity
- High-dose vitamin E (supplement) interfere with Vitamin K activity in blood clotting,
increasing risk of hemorrhaging (see explanation in vitamin K section)
- High-dose vitamin E (supplement) enhance blood thinning medication activity with
the same outcome
DIGESTION, ABSORPTION, TRANSPORT AND EXCRETION OF VITAMIN K
Absorption and transport
- Since K1 is mainly found in green leafy vegetables, absorption can be impaired by
plant tissue (bound to chloroplast), unless in presence of fat in the meal. Vitamin K is
otherwise found in vegetable oils (soybean, canola)
- 80% of dietary vitamin K absorbed in small intestine, via micelle (lipase and bile
activity required)
- Taken in chylomicrons through the lymphatic system to the liver
- Colonic bacteria produced menaquinones: absorbed in the colon by passive
diffusion
- Transported via lipoproteins (VLDL and LDL) to peripheral tissue
• Storage: Minimal, some in the liver. Recycled rapidly by the K-epoxide cycle for
optimal re-use
• Excretion: Primarily via bile in faeces, small amount in urine
vitamin K functions
- Primary function as co-factor of the carboxylase
enzyme in the synthesis of blood-clotting factors;
in the conversion of pre-prothrombin to
prothrombin in the liver - In bone health: vitamin K is a co-factor in
carboxylation of the glutamic amino acid in
extra-hepatic vitamin K dependent proteins
involved in bone structure: e.g. osteocalcin
Vitamin K is the
cofactor of the
carboxylase
The medication Warfarin inhibits the enzyme enzyme
epoxide reductase which reduces oxidised
vitamin K
Vitamin K deficiency
Deficiency
- May increase risk of osteoporosis /fracture
- Risk of hemorrhaging
- Precaution in new-born baby: injection at birth to
prevent bleeding. Why is this measure required?
- Can be due to long term antibiotic use, or fat
malabsorption disease
Vitamin K interaction toxicity
Nutrient interaction
- High-dose (supplemental) vitamin A interferes with
vitamin K absorption from GIT
- High-dose (supplemental) vitamin E interferes with
vitamin K activity on clotting factors
Toxicity
- No UL as no known toxicity
Menaquinones are more biologically active than phylloquinones
False
vitamin K
How many international units are equivalent to 1650 micrograms of retinol equivalent?
+/-
0 (5500 - 5500)
How much betacarotene (in μg) is there in 4000 IU of vitamin A from vegetarian source?
+/-
0 (7200 - 7200)
Which of the following is a natural rich food source of vitamin D?
Answers:
1.
Dark leafy green vegetables
- Yellow-orange vegetables
- Enriched cereal products
- Fortified milk products
- Salmon and sardines
Correct5.
Salmon and sardines
Which of the following vitamin forms has hormone-like functions?
Answers:
1.
Phylloquinone
- Tocotrienol
- Calcitriol
- Menaquinone
- Retinol
Correct3.
Calcitriol
Vitamin D must be hydroxylated first in the kidney and then in the liver to become biologically active
CorrectFalse
Response Feedback:
Read the statement properly: the first hydroxylation is in the liver
Calcitriol functions in calcium and bone metabolism by:
.
Increasing vitamin A absorption from the GIT
- Increasing calcium excretion by the kidney
- Reducing calcium and phosphorus losses through feaces
- Reducing release of calcium from the bone
- Increasing calcium absorption from the GIT
Correct5.
Increasing calcium absorption from the GIT
The family of compounds known as vitamin K include [A] All Answer Choices Tocopherols and tocotrienols Retinol, retinal, and retinoic acid Phylloquinones and menaquinones Cholecalciferol and calcitriol Phyllopherols and tocoquinones
The family of compounds known as vitamin K include Correct Phylloquinones and menaquinones
What are characteristic differences between fat and water soluble vitamins?
1.
All of these are correct.
- Toxicity risks
- Type of transport from the GIT
- Storage in the body
- Mechanisms of absorption
Correct1.
All of these are correct.
Vitamin D supplementation excess leads to toxicity signs and symptoms, such as
1.
Decreased calcium absorption
- Increased vitamin D excretion
- Hypocalcemia
- Hypercalcemia
- Liver damage
Correct4.
Hypercalcemia
Which of the following vitamins is synthesised endogenously?
1.
Ergocalciferol
- Betacarotene
- 7-dihydroxycholesterol
- Alpha-tocopherol
- Calcitriol
Correct5.
Calcitriol
To become biologically active: [A]
Vitamin E must be hydroxylated in the kidney and liver
Vitamin K must be hydroxylated in the liver and kidney
Vitamin D must be hydroxylated in the kidney and liver
Vitamin K must be hydroxylated in the kidney and liver
Vitamin D must be hydroxylated in the liver and kidney
Vitamin D must be hydroxylated in the liver and kidney
The key point here is to remember that vitamin D is the vitamin that requires hydroxylation for activation, and that the first one occurs in the liver, followed by the kidney
Rhodopsin, the visual pigment in the retina of the eye, is regenerated when opsin combines with:
.
Beta-carotene
- 11-cis retinal
- Trans-retinal
- 13-cis-retinol
- Retinoic acid
Correct2.
11-cis retinal
How many micrograms of 25,hydroxyvitamin D3 is there in 3000 IU?
+/-
0 (15 - 15)
When measuring the vitamin D status of an individual, the molecule measured is:
1.
Calcitriol
- Cholecalciferol
- 25-hydroxy-vitamin D3
- 1,25 dihydroxy-vitamin D3
- Vitamins D2 + D3
Correct3.
25-hydroxy-vitamin D3
Vitamin D deficiency in adults results in a condition called:
.
Hypercalcemia
- Osteoporosis
- Hypercalcification
- Ricket’s disease
- Osteomalacia
Correct5.
Osteomalacia
As calcium levels in the blood drop below the normal range which vitamin is activated to increase calcium absorption?
1.
K
- D
- Carotenoids
- Retinol
- E
D
How many μg of retinol equivalent are there in 4000 IU?
0 (1200 - 1200)
Response Feedback:
Review the vitamin A section of the lecture material and practice the conversions
The family of compounds known as vitamin E include: [A] Phyllopherols and tocoquinones Cholecalciferol and calcitriol Retinol, retinal, and retinoic acid Tocopherols and tocotrienols Phylloquinones and menaquinones
Tocopherols and tocotrienols
