Download LEARNING OBJECTIVES Vitamin B12, Folic Acid and B6 • To

LEARNING OBJECTIVES
Vitamin B12, Folic Acid and B6
•
To describe the sources, Recommended Daily Allowance and Chemical
nature of Vitamin B12, Folic Acid & Vitamin B6
•
To explain the absorption of B12, Folic acid & Pyridoxine
•
To discuss the metabolism of B12, folic acid & B6
•
To describe the deficiency states of B12, folic acid & B6
LECTURE OUTLINE
Vitamin B12, Folic Acid and B6
Vitamin B12 or Cyanocobalamin
Source:

Only synthesized by bacteria

Other source is food derived from animals e.g. Liver, Eggs, Milk, Seafood,

Complex Core ring with Cobalt in centre.
Absorption of B12
Intrinsic factor from Parietal cell
proteins in Blood


B12 from Diet
B12 complex in Ileum


B12 Binding
Mucosal cells
Actions

Synthesis of Methionine from Homocysteine

Isomerization of methyl malonyl CoA from odd Carbon numbered fatty acids.
When B12 is deficient these fatty acids accumulate in cell membrane of C.N.S
Causing Neurologic symptoms.
Folate trap
•
Hazards of B12 deficiency are more evident in mitotically active cell like bone
marrow & intestine. Such tissues need methylene & formyl THF for DNA
Replication
•
In B12 deficiency N5 Methyl from is not used & accumulates and leads to
MEGALOBLASTIC ANEMIA.
Methyl Synthase
•
Homocysteine
Methionine
Methyl Cobalamin
Pernicious Anemia
•
Occurs due to autoimmune destruction of parietal cells
•
Patients presents with neuro-psychiatric symptoms
•
Folic acid & B12 deficiency symptoms MIMIC. So if not sure give B12 first to
HALT CNS Symptoms or at least a combination.
•
Deficiency occurs in Sprue, Enteritis, Diphyllobothrium latum
•
RDA  3μg/day, 6μg/day in Pregnancy & Lactation
Folic Acid
Source:
•
Green leafy vegetables, liver, whole grain cereals.
•
Active form is THF acid produced by 2 step Reduction of folate by
DIHYDRO folate Reductase
Actions:
THF recieves on carbon donars as serine, Histidine & Glycine transfers them
for synthesis of
•
Amino Acids
•
Purines
•
Thymidine
Deficiency:
Characterized by Megaloblastic anemia & growth failure
CAUSES
•
Increase Demand e.g. pregnancy, lactation
•
Pathology of small Intestine
•
Alcoholism
•
Dihydrofolate Reductase Inhibitors
Fetal Neural Tube Development: Is dependent on folic acid 0.4 mg/day for all
pregnant women
•
RDA 
100μg/day
•
500 - 800μg in pregnancy & lactation.
Vitamin B6 or Pyridoxine
Sources:
Dried yeast, Rice Polishing, wheat germs, cereals, Oil seeds, green leafy
vegetables, egg, milk, meat fish and bacterial synthesis in small intestine.
Functions:
•
Protein metabolism: Active form of vitamin B6 is PLP i.e. pyridoxal phosphate
which is involved in transamination, decarboxilation.
•
Heme synthesis: ALA synthase enzyme is PLP dependent enzyme. This is
the rate limiting step in heme synthesis. Vitamin B6 deficiency is commonly
associated with anemia.
•
Transulfuration, desulfhydration, production of Niacin.
Deficiency:

Neurological Manifestation like Demyelination of nerves.

Can cause hypochromic microcytic anemia because of inhibition of heme
biosynthesis.
RDA:
o Male

2 mg
o Female

1.5 mg