ASCORBIC ACID (VITAMIN C)

  

INTRODUCTION:  Vitamin C is a water soluble vitamin which is easily destroyed by heat, alkali and storage. In the process of cooking, 70% of vitamin C is lost. It is a reducing agent and it’s strong reducing property depends on the double-bonded (enediol) carbons.

METABOLISM OF ASCORBIC ACID: Ascorbic acid is readily absorbed from gastrointestinal tract. The vitamin is excreted in urine. Since vitamin C is a strong reducing agent, the Benedict's test will be positive in the urine sample after the vitamin administration.

Oxidation of ascorbic acid yields dehydro ascorbic acid, which is oxidized further to oxalic acid. Ascorbic acid is partly excreted unchanged and partly as oxalic acid. Most of the oxalates in urine are derived from ascorbic acid, and the rest from glycine metabolism. The ascorbic acid level varies between 0.7 to 1.2 mg/100 ml of plasma and 25 mg/100 cc of WBC. A low level in blood is noted in women taking contraceptive pills and also in chronic alcoholics.

BIOCHEMICAL FUNCTIONS OF VITAMIN C

1)  Reversible oxidation-reduction:  It can change between ascorbic acid and dehydroascorbic acid.

2)  Hydroxylation of proline and lysine: Ascorbic acid is necessary for the post-translational hydroxylation of proline and lysine residues. Hydroxyproline and hydroxylysine are essential for the formation of cross links in the collagen, which gives the tensile strength to the fibres. This process is absolutely necessary for the normal production of supporting tissues such as osteoid, collagen and intercellular cement substance of capillaries.

3)  Tryptophan metabolism:  Ascorbic acid is necessary for the hydroxylation of tryptophan to 5-hydroxy tryptophan. This is required for the formation of serotonin.

4.  Tyrosine metabolism:  Vitamin C helps in the oxidation of parahydroxy phenyl pyruvate to homogentisic acid.

5.  Iron metabolism:  Ascorbic acid enhances the iron absorption from the intestine.

6.  Hemoglobin metabolism:  It is useful for re-conversion of met-hemoglobin to hemoglobin.

7.  Folic acid metabolism:  Ascorbic acid is helping the enzyme folate reductase to reduce folic acid to tetrahydrofolic acid. Thus it helps in the maturation of RBC.

8.  Steroid synthesis:  Large quantities of vitamin C are present in adrenal cortex. The ascorbic acid is depleted by ACTH stimulation. So the vitamin has some role in adrenal steroidogenesis. Vitamin C helps in the synthesis of bile acids from cholesterol. The initial 7-alphahydroxylase step is stimulated by the vitamin.

9.  Phagocytosis: Ascorbic acid stimulates phagocytic action of leukocytes and helps in the formation of antibodies.

10.  Anti-oxidant property: As an anti-oxidant, it may prevent cancer formation. Aniline dyes are known to induce bladder cancer in factory workers. Daily intake of vitamin C reduces this risk for cancer.

11.  Cataract:  Vitamin C is concentrated in the lens of eye. Regular intake of ascorbic acid reduces the risk of cataract formation. Deficiency Manifestations of Vitamin C results in scurvy and Infantile scurvy (Barlow's disease).

RELATED;

1.  Vitamin A

2.  Magnesium

3.  Calcium and the human body

4.  Biomolecules of life

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