Vit K Flashcards
What is the definition of Vitamin K?
Fat-soluble vitamin essential for blood clotting, bone metabolism, and cardiovascular health.
What are the main functions of Vitamin K?
- Coenzyme for post-translational carboxylation of glutamic acid residues in proteins
- Essential for calcium binding proteins involved in blood coagulation and bone health
What is Vitamin K1 also known as? how is it stored/transported in the body?
Phylloquinone
-stored in the liver (limited storage), transported in chylomicrons
Where is Vitamin K1 primarily found in food?
- Green leafy vegetables
- Plant oils
What is Vitamin K2 also known as? how is it different from K1?
Menaquinone
-it is more bioavailable and is transported in LDL/HDL
How is Vitamin K2 produced?
Produced by intestinal bacteria
What key property of Vitamin K allows for its absorption?
Fat-soluble vitamin stored in the liver
What enzyme is involved in the gamma-carboxylation of glutamic acid residues? what enzyme reduces vit K back to its preffered form? what is the purpose of this rxn?
Gamma-glutamyl carboxylase
VKOR
-carboxylation of glutamic acid produces a (-) charge, allows Ca2+ to bind for biological activity
What process allows Vitamin K to be reused in the body? explain the steps. what is an inhibitor of this cycle?
The Vitamin K cycle
- Vitamin K is reduced to Vitamin K hydroquinone (KH₂).
- KH₂ acts as a coenzyme for gamma-carboxylation of glutamate residues in proteins.
- This process creates γ-carboxyglutamic acid (Gla), enabling calcium binding.
- Vitamin K is converted to Vitamin K epoxide, which is recycled by Vitamin K epoxide reductase (VKOR).
Warfarin (a blood thinner) inhibits VKOR, preventing Vitamin K recycling, reducing clotting ability
Which factors in the coagulation cascade depend on Vitamin K?
- Factor II (Prothrombin)
- Factor VII (Proconvertin)
- Factor IX (Christmas factor)
- Factor X (Stuart factor)
What is Osteocalcin? what is the impact of vit K on it?
Small protein synthesized by osteoblasts, that repair bone
-dependent on Vitamin K for activation
What is the role of Matrix Gla Protein (MGP)? what affect does Vit K have on it?
MGP has a high affinity for Ca2+ and is essential for bone structure. However, in excess it can cause calcification in vessels
Vit K Inhibits abnormal calcification of arteries and soft tissues
How is Vitamin K absorbed in the body? how does storage differ between K1/K2?
Absorbed in the jejunum, requiring bile salts and lipids -> transported by chylomicrons -> incorporated into LDL / HDL for circulation
K1 ~10% of liver storage (limited storage)
K2 ~the rest
What is the Adequate Intake (AI) of Vitamin K for adult men and women?
120 μg/day for men and 90 for women
What is a common cause of Vitamin K deficiency in newborns?
- Low placental transfer of Vitamin K.
- Lack of gut bacteria in newborns.
What are symptoms of Vitamin K deficiency?
- Increased bleeding tendency
- Prolonged prothrombin time
- Abnormal bone metabolism
What is Warfarin used for? how does it work?
An anticoagulant used to prevent blood clots
-Warfarin blocks Vitamin K epoxide reductase (VKOR), preventing the recycling of Vitamin K back to its active form
What should Warfarin users do to manage their Vitamin K intake?
Maintain consistent Vitamin K intake to avoid altering Warfarin effectiveness
What is the primary method to assess Vitamin K status? How does it work? what other marker of Vit K status are there?
Prothrombin Time (PT test)
-Measures time taken for blood to clot.
Not a specific test for Vitamin K but used in clinical settings.
- serum Phylloquinone Levels:
Half-life is <8 hours, making it not a good long-term marker
-Undercarboxylated Proteins (PIVKA-II Test):
Protein Induced by Vitamin K Absence-II (PIVKA-II) levels >3 ng/mL indicate deficiency.
What does an increase in Protein Induced by Vitamin K Absence-II (PIVKA-II) indicate?
levels >3 ng/mL indicate
Vitamin K deficiency
What are the richest food sources of Vitamin K1and K2?
Vitamin K1 (Phylloquinone):
-Green leafy vegetables (spinach, kale, broccoli, turnip greens).
-Cooking oils (canola, olive, soybean)
Vitamin K2 (Menaquinone):
-Fermented foods (natto, cheese).
-Animal products (liver, dairy, egg yolks).
What is the half-life of serum Phylloquinone? why does this matter?
Less than 8 hours
- this means that it is not a good marker for long term levels
True or False: There is an established Upper Limit (UL) for Vitamin K.
False
-No Upper Limit (UL) for Vitamin K
how can liver disease impact vit K?
1) Impaired fat absorption due to reduced bile production, leading to poor Vitamin K absorption.
2) Decreased production of Vitamin K-dependent clotting factors (Prothrombin, Factors VII, IX, and X).
3) Even with adequate Vitamin K intake, the liver may not efficiently synthesize clotting proteins if liver damage is sever
