Vitamin K, Sources of Vitamin K, RDA of Vitamin K, Biochemical functions of Vitamin K, Dietary Sources of Vitamin K , Hypervitaminosis of Vitamin K

1. VITAMIN K
DR NERUSU SAI PRIYANKA
MPT NEUROSCIENCES

2. INTRODUCTION
 Vitamin K is the only fat soluble vitamin with a specific coenzyme function. It
is required for the production of blood clotting factors, essential for
coagulation.
 Vitamin K1 (phylloquinone) is present in plants.
 Vitamin K2 (menaquinone) is produced by the intestinal bacteria and also
found in animals.
 Vitamin K3 (menadione) is a synthetic form.
 All the three vitamins (K1, K2, K3) are naphthoquinone derivatives.
 The three vitamins are stable to heat.
 Their activity is, however, lost by oxidizing agents, irradiation, strong acids
and alkalies.

4. ABSORPTION, TRANSPORT AND STORAGE
 Vitamin K is taken in the diet or synthesized by
the intestinal bacteria.
 Its absorption takes place along with fat
(chylomicrons) and is dependent on bile salts
 Vitamin K is transported along with LDL and is
stored mainly in liver and, to a lesser extent, in
other tissues.

5. BIOCHEMICAL FUNCTIONS
 The functions of vitamin K are concerned with blood clotting
process.
 It brings about the posttranslational (after protein biosynthesis in
the cell) modification of certain blood clotting factors.
 The clotting factors II (prothrombin), VII, IX and X are synthesized
as inactive precursors (zymogens) in the liver.
 Vitamin K acts as a coenzyme for the carboxylation of glutamic
acid residues present in the proteins and this reaction is catalysed
by a carboxylase (microsomal).
 It involves the conversion of glutamate (Glu) to gamma -
carboxyglutamate (Gla) and requires vitamin K, O2 and CO2 .
 The formation of gamma carboxyglutamate is inhibited by
dicumarol, an anticoagulant found in spoilt sweet clover.
 Warfarin is a synthetic analogue that can inhibit vitamin K action .

7. BIOCHEMICAL FUNCTIONS
 Vitamin K is also required for the carboxylation of
glutamic acid residues of osteocalcin, a calcium binding
protein present in the bone.
 The mechanism of carboxylation is not fully understood.
 It is known that a 2,3-epoxide derivative of vitamin K is
formed as an intermediate during the course of the
reaction.
 Dicumarol inhibits the enzyme (reductase) that converts
epoxide to active vitamin K.

9. ROLE OF GLA IN CLOTTING
 The gamma-carboxyglutamic acid (Gla) residues of
clotting factors are negatively charged (COO–) and they
combine with positively charged calcium ions (Ca2+) to
form a complex.
 The mechanism of action has been studied for
prothrombin.
 The prothrombin Ca complex binds to the phospholipids
on the membrane surface of the platelets.
 This leads to the increased conversion of prothrombin to
thrombin.

10. RECOMMENDED DIETARY ALLOWANCE (RDA)
Strictly speaking, there is no RDA for
vitamin K, since it can be adequately
synthesized in the gut.
Accordingly, the suggested RDA for
an adult is 70-140 Micro g/day.

11. DIETARY SOURCES OF VIT K
 Cabbage
 Cauliflower
 Tomatoes
 Alfa Alfa
 Spinach and other green vegetables are good sources.
 It is also present in egg yolk, meat, liver, cheese and dairy
products.

12. DEFICIENCY SYMPTOMS
 Vitamin K deficiency may occur due to its
 Faulty absorption (lack of bile salts)
 Loss of vitamin into feces (diarrheal diseases) and
 Administration of antibiotics (killing of intestinal flora).
 Deficiency of vitamin K leads to the lack of active prothrombin in
the circulation. The result is that blood coagulation is adversely
affected.
 The individual bleeds profusely even for minor injuries.
 The blood clotting time is increased.

13. HYPERVITAMINOSIS K
Administration of large doses of
vitamin K produces hemolytic
anaemia and jaundice, particularly
in infants.
 The toxic effect is due to increased
breakdown of RBC.

14. ANTAGONISTS OF VITAMIN K
 The compounds—namely heparin,
bishydroxycoumarin— act as anticoagulants and
are antagonists to vitamin K.
 The salicylates and dicumarol are also
antagonists to vitamin K.
 Dicumarol is structurally related to vitamin K and
acts as a competitive inhibitor in the synthesis of
active prothrombin.

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