by Tarek Musslimani

Created on: December 09, 2009   Last Updated: January 19, 2010

Vitamins are organic compouds which are important for the normal metabolism inside our body.  They function there as coenzymes.  Vitamins are divided according to their solubility in water and lipids.  There are water soluble vitamins and fat soluble vitamins.  

Fat soluble viatamins are designated vitamins A,D,E, and K.  Water soluble vitamins are the B vitamins and vitamin C.  Vitamins B include: thiamine, riboflavin, nicotinamide, pyridoxine and folic acid and vitamin B12.

Vitamin A or retinol is important for normal vision.  It is absorbed in the intestine and is transported to the liver for storage.  The clinical manifestation of vitamin A deficiency includes night vision loss which is called medically nyctalopia.  In complete deficiency of vitamin A vision during the day is also lost.  Vitamin A is lipid soluble.

Another important vitamin and which is lipid soluble is vitamin D.  This vitamin is important for the bone metabolism.  It facilitates the absorption of calcium ions in the intestine. 

It has two sources.  One is from the diet and the other is from exposure of the skin to UV radiation from the sun.  One of the disorders of vitamin D deficiency is called rickets.  It is common in children.  Osteomalacia is a similar disease which occurs in the elderly people.

Vitamin D overdose can lead to hypercalcemia with its consequences of deposition of calcium salts in different body tissues such as the kidney and the blood vessels.  Thus forming stones in these tissues.

Vitamin K is another lipid soluble vitamin.  It is important for the proper function of an enzyme that is responsible for the synthesis of clotting factors for the blood.  Deficiency of this vitamin can occur due to malabsorption or due to administration of antibiotics.

Bacteria in the intestine usually secrete vitamin K analogues in the intestine.  Killing these bacteria by the administration of antibiotics can lead to shortage of vitamin K and subsequently to hemorrhage symptoms.  The presence of vitamin K antagonists such as those poisons used to kill rats can lead to vitamin K deficiency.

Vitamin E is another fat soluble vitamin.  It functions as an antioxidant in the cells.  Thus it can protect the cell from the effect of free radicals that can be generated from ionizing radiation such as UV radiation. 

Vitamin C is a water soluble vitamin. 

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