What is Cholesterol?
Cholesterol is a waxy material that is found in many food items including milk, cheese, eggs, butter, fish, beef, pork, chicken and goat meat . It is a naturally occurring, fat like substance with a complex chemical formula, and is used to build cells and make hormones.
Some amount of cholesterol is necessary for the proper functioning of the body cells. For example, the presence of cholesterol is essential for the formation of sex hormones and vitamin D and metabolism in the body. In young children, cholesterol is required for the development of the brain cells. The membranes of many cells require a minimum quantity of cholesterol for healthy functioning.
Sources and Metabolism of Cholesterol
Cholesterol in the blood comes from the two main sources:
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The cholesterol ingested from outside, that is, taken in the daily diet. An average vegetarian consumes between 200-400 mg of cholesterol daily, while a non vegetarian usually consumes between 400-600 mg of cholesterol.
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A large part of the cholesterol in the blood comes from the cholesterol production within the liver; it has been seen that if the oral intake of cholesterol through food is reduced, the liver tends to produce a little extra cholesterol at least, during the initial few weeks.
The mechanism of metabolism of cholesterol is rather complex and involves several complicated pathways, receptors, and enzyme actions. Cholesterol itself cannot be dissolved in blood or water. Like many other food particles, after absorption from the intestine, the dietary fat and cholesterol are transferred to the liver for further metabolic action. In the liver, cholesterol combines with water soluble substances called apolipoproteins and phospholipids to form chlyomicrons. They are a form of complex particles called lipoproteins that is fats and they are combined with proteins.
Types of Lipoproteins
Three types of lipoproteins carry cholesterol from the liver through the blood circulation to the different parts of the body. These three lipoproteins play a major role in causing heart disease. They are distinguished from one another when the blood is centrifuged. Very dense particles settle down and the low density ones remain on the top.
Very Low Density Lipoprotein:
Large fat particles also called as chylomicrons, triglycerides and fatty acids from VLDL. As the name suggests, these particles have very low density and weight. Some of the VLDL is used for energy; the other is stored in the fat deposits. A good portion of ALDL is returned to the liver for excretion. VLDL is converted into intermediate density lipoprotein.
Low Density Lipoprotein
LDL is a product of VLDL after the removal of triglycerides. LDL is the most cholesterol rich lipoprotein in the blood. A portion of the LDL is used for the fat storage; the rest is sent back to the liver for the excretion. Excessive accumulation of LDL in the blood is definitely harmful, since it gets deposited in the walls of the blood and slowly results in clogging and narrowing of the arteries.
High Density Lipoprotein:
HDL is often referred to as ‘good ‘cholesterol. It is formed in the liver and walls of the small intestine. While maturing in the blood stream, it obtains cholesterol from the surrounding tissues. The blood circulation then transports the HDL back to the liver, from where the cholesterol is excreted in the bile. This is how HDL cleanses the body and helps a person get rid of excessive amount of cholesterol.