In this article we will discuss about the functions of choline in human body.
It was first isolated by Stracker in 1849 from body fluids. It has got the following formula. It is a component of lecithin. Sphingomyelin, acetylcholine, etc., Butter, nervous tissue, yolk of eggs is very rich sources. It can be easily synthesised in the human body from methionine and ethanolamine.
i. Lipotropic Action:
Choline prevents the deposition of fats and accelerates the rate of removal of fat from the liver. Betaine, methionine, inositol, casein and certain other proteins are also lipotropic. The lipotropic action of choline has been studied in various ways, all of which shows that choline helps in the synthesis of phosphatides in the liver and to a lesser extent in other tissues. In this way it accelerates the rate of phospholipid formation and mobilization of fat.
Methionine exerts its effects by transferring its methyl group to ethanolamine, with the formation of choline. Betaine also acts similarly as a methyl donor. Inositol has similar action on a fat-free diet. Under certain conditions vitamin B12 and folic acid have lipotropic action. The lipotropic effect of casein is due to its methionine content.
Pancreatic extracts have been found to have strong lipotropic action, as they contain choline, methionine, inositol, lipotropic proteins and certain unidentified factors. This action of lipotropic substances, specially the easily available choline, is of considerable practical importance. Because it enables us to control the amount of liver fat by dietary means, and consequently may have a useful application in the treatment of fatty liver.
As found in rats, only small amount of choline is enough. A dose of 5 mgm of choline per day has been found to prevent a rise of 12% of fat in the liver. When these lipotropic factors are absent in the diet, liver become fatty and young animals develop haemorrhagic lesions in the skin, kidney and other tissues which may be fatal. Fibrotic changes appear in the liver due to prolonged lack of choline.
It is to be noted that cholesterol and cysteine exert an antilipotropic action and cause deposition of fat in the liver and various other tissues. In nature, cholesterol and lecithin (which contains choline) are constantly associated. This is important because they maintain a balance between the lipotropic and antilipotropic factors.
ii. Synthetic Functions:
Compounds of immense physiological importance are synthesised from choline, viz. lecithin, sphingomyelin, acetylcholine, etc. The first two belong to the group of phospholipids.
Acetylcholine is of utmost importance for the following:
a. Maintains Functional Integrity of the Nervous System:
Formation and destruction of acetylcholine and probably of other choline derivatives—which take place normally at all synapses—are believed to be responsible for the transmission of the nerve impulses through the synapses and thereby maintain the functional continuity of the nervous system.
b. Essential for Cholinergic Fibers:
It is produced at the motor ending (muscle or gland) of the parasympathetic fibres and certain sympathetic fibers and initiates their peripheral activities (i.e., contraction of plain muscles or secretion of relevant glands).
c. Helps Contraction of Skeletal Muscles:
Acetylcholine is produced at the myoneural junction of the skeletal muscles and initiates the chemical changes causing muscular contraction.
iii. Vitamin Action:
Choline is supposed to be a member of the vitamin B family and acts as a methyl donor in transmethylation.
iv. Essential Constituent of Diet:
Essential constituent of diet for lower animals, specially when supply of methionine is low. It promotes growth, controls storage and mobilisation of fat and other important physiological processes in them. Although it serves the same functions in man, yet it is not essential, because it can be synthesised in the human body.