by Tarek Musslimani

Created on: January 24, 2008   Last Updated: January 19, 2010

Vitamins are essential compounds for the metabolism of humans body. There are water soluble vitamins and lipid soluble vitamins. Water soluble vitamins have been extensively studied and its chemistry is well known. On the other hand, lipid vitamins are less studied and its chemistry is less understood than its water soluble counterpart. This is mainly because the research on lipid soluble vitamins causes technical problems. The importance of vitamins manifests itself in the diseases that the lack of theses vitamins make in the body. For example, the lack of vitamin C or ascorbic acid in the diet can make scurvy in humans. While nicotinic acid deficiency, another water soluble vitamin can cause pellagra, a skin disease. Water soluble vitamins are called hydrophilic vitamins, that is to say they like water, while lipid soluble vitamins are called hydrophobic vitamins, that is to say they dislike water. There are four lipid soluble vitamins, and these are vitamins A,D, E, and K, while the rest of the vitamins are water soluble. Some of the vitamins are required for synthesis of coenzymes, these are compounds that without them enzymes cannot function properly. Water soluble vitamins in addition to vitamin C and nicotinic acid are riboflavin or vitamin B2 which its deficiency can cause growth retardation in children. The vitamin pantothenate or vitamin B3 is responsible for causing dermatitis in chicken if deficient in the diet. Another water soluble vitamin is thiamine or vitamin B1, which its deficiency can cause beriberi. Pyridoxal or vitamin B6 is another water soluble vitamin which its deficiency in the diet has rendered dermatitis in experimental rats. Biotin is an important water soluble vitamin which its deficiency causes dermatitis in humans. Folate or folic acid is an important vitamin in the biosynthesis of nucleic acids. Its deficiency can cause anemia of the blood in humans. Another vitamin that causes pernicious anemia in humans is B12 or cobalamin. B12 is also important for the proper functioning of the nervous system. Vitamin C was shown to be related to scurvy. Most animals can synthesize vitamin C. However, guinea pigs and humans do not have this ability. Vitamin C is found in citrus juice. As was mentioned earlier lipid soluble vitamins include vitamins A,D, E, and K. Vitamin A is obtained from the diet indirectly as beta-carotene or directly from eggs and liver products. Yellow vegetables have beta-carotene. Vitamin A exists in three oxidation states or three compounds. these compounds differ in the terminal -OH group. These compounds are called retinol, retinal and retinoic acid. All of these compounds or vitamin A forms have biological function in the body. Retinol and retinoic acid have cellular function of gene expression during cell differentiation. Retinal on the other hand is a light sensitive compound. It has an important role in vision. Another lipid soluble vitamin is vitamin D. It has a role in the absorption of calcium in the intestine. Therefor its importance in in bone formation and metabolism. The lack of vitamin D can cause rickets in children and osteomalacia in adults. The third lipid soluble vitamin is vitamin E. Its important function is to trap free radicals that form during matabolism. Therefor it is important as an antioxidant. This function prevents damage to fatty acids in tissue. Its deficiency can cause fragile red blood cells and neurological problems. The last vitamin in this series is vitamin K. It is important in the process of blood coagulation. There are medical analogues of vitamin K which are used to prevent excessive blood clotting.

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