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Cholesterol is a steroidal lipid molecule that involves in the building and maintenance of cell membranes of the body. It is a precursor for synthesis of various important chemical compounds. It also involves in several other physiological functions of the body. Within the body, cholesterol is synthesized in endoplasmic reticulum of the various cells from acetyl-CoA using HMG-CoA or mevalonic acid pathway. The main sources are liver, adrenal gland, intestine, brain and reproductive system. Cholesterol is also obtained from diet, mainly from animal products like milk, creams, egg and meat. Cholesterol is not present in plant sources. Fruits and vegetables contain very less amounts of fats.
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Involves in construction and integration of cell membranes
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Provides structural and physical balance of cell membranes
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It is a precursor for synthesis of sex hormones
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It is a precursor for synthesis of bile
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It involves in metabolism of fat soluble vitamins like vitamin A, D, E and K
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· Involves in insulating myelin sheath of the nerves
Lipoproteins are lipids that are linked to protein molecules. Cholesterol should be traveled in the blood to various cells and tissues of the body. Due to its hydrophobic nature, it cannot travel alone in the blood stream. Therefore, it should be linked to plasma proteins and form lipoproteins. These lipoproteins are carried through blood and deliver cholesterol to targeted cells.
There are three types of cholesterol
Low Density Lipoprotein (LDL) - Cholesterol
High Density Lipoprotein (HDL) - Cholesterol
Very Low Density Lipoprotein (VLDL) - cholesterol
Cholesterol is circulated in the form of lipoproteins in the blood. Low density lipoproteins (LDL) are known to carry cholesterol to various cells of the body. If there is an excess amount of LDL circulating in the blood, they deposit on blood vessels. Further, they damage, obstruct blood vessels and restrict the blood flow. Therefore, Low density lipoproteins (LDL) are referred as LDL cholesterol or bad Cholesterol.
From various cells of the body, High density lipoproteins (HDL) carry cholesterol to liver. From the liver, cholesterol is excreted into intestine along with bile. Since HDL removes cholesterol from blood it is referred to good cholesterol.
Very low density lipoproteins (VLDL), like LDL and HDL, contains cholesterol, protein and triglyceride. VLDL contains more of triglycerides. Therefore, VLDL also considered as bad cholesterol.
High Density Lipoproteins (HDL) are considered as good cholesterol. High density lipoproteins (HDL) carry cholesterol to liver. From the liver, cholesterol is excreted into intestine along with bile. Since HDL removes cholesterol from blood, it is referred to good cholesterol.
High levels of circulating Low Density Lipoproteins (LDL) and Very Low Density Lipoproteins (VLDL) accumulate on blood vessels. Further, they damage, obstruct blood vessels and restrict the blood flow. Therefore, the Low density lipoproteins (LDL) and Very low density lipoproteins (VLDL) are referred as bad Cholesterol.
According to American Heart Association guidelines, plasma cholesterol levels are:
Total cholesterol < 200 mg/dl (desirable) (above> 200mg/dl risk of heart disease)
Total cholesterol = LDL + HDL + VLDL
Low Density Lipoproteins (LDL) <100 mg/dl (optimal) (above> 100mg/dl risk of heart disease)
High Density Lipoproteins (HDL) > 40 mg/dl for males (and) >50 mg/dl for females (optimal) (below<40 mg/dl risk of heart disease)
Triglycerides < 150 mg/dl (optimal) (above>150mg/dl risk of heart disease)
High levels of fats or cholesterol is called hyperlipidemia. Specifically, elevated levels of cholesterol above normal levels are termed as hypercholesterolaemia.
Lipid profile is a group of tests performed to measure the different types of cholesterol levels in blood plasma. Lipid profile provides information about whether a person is at risk of heart diseases or other health problems. A lipid profile includes estimation of blood plasma total cholesterol, Low Density Lipoproteins (LDL), High Density Lipoproteins (HDL) and Triglycerides.
Chemically, fats and oils are triglycerides (triacetylglycerols with three long chain carboxylic acids). When they are hydrolyzed, they give glycerol and fatty acids. Glycerol is converted to glucose in the liver. Fatty acids are transported to fatty tissues or adipose tissues and are stored. These provide energy when body requires additional energy.
Triglycerides less than 150 mg/dl are considered optimal. Above 150mg/dl, there could be risk of heart disease and other health problems like diabetes.
High cholesterol levels and High triglycerides are risk factors of heart diseases and other health problems like diabetes.
Cholesterol can be reduced by maintaining proper diet, physical activity and by modifying life style changes.
Diet: Diet from plant sources doesn’t contain cholesterol. Moreover, fruits and vegetables contain fewer amounts of fats. Therefore, diet containing more amounts of fruits and vegetables and reducing intake of animal products is one way of reducing cholesterol.
Replace high fat foods with fruits and vegetables.
Physical activity: A daily moderate to vigorous exercise for half an hour or more also is one of the ways to reduces high cholesterol.
Check Body Mass Index BMI and try to keep optimal weight
Life style
If you have a habit of smoking and drinking heavily, try to avoid them. Smoking is found to decrease high density lipoproteins (HDL). HDL is good cholesterol. Decreasing HDL is risk factor of heart disease. Alcohol increases the plasma triglycerides.
Avoid smoking and excess alcohol drinking
Cholesterol is required to maintain cell structure and other physiological functions. Therefore, target of reducing cholesterol should be focused when cholesterol levels are higher than normal levels. There are few over the counter products available for reducing cholesterol. However, it is important that you contact your physician if you have abnormal lipid profile. Some of the OTC products include Niacin, Garlic preparations, Phytosterols, Pectin, Lecithin and Vitamin C. You need to check if the food and drug administration or other authorized body have suggested for use. For example, US FDA requires a statement on the label of herbal and dietary products that “This product has not been evaluated by the FDA. It is not intended to diagnose, treat, cure or prevent.”
Prescription medications are available for lowering cholesterol. Those fall in different categories
Bile acid sequestrants : Cholestyramine (e.g.: Cholestyramine light), colestipol (e.g.:Colestid), colesevelam (e.g.:Welchol)
HMG-CoA reductase inhibitor or Statins: Lovastatin, Pravastatin, Simvastatin, Atorvastatin, Fluvastatin
e.g. brand names Lipitor, Lescol, Mevacor, altocor, Zocor, Crestor
Fibric acid derivatives : Gemfibrozil (e.g.: Lopid), fenofibrate (e.g.: Tricor, Triglide, Lofibra), clofibrate (e.g.: Atromid- S)
Nicotinic acid (E.g.: Niacor, Nicolar)
Bile acid sequestrants are insoluble and non-absorbable anion exchange resins. These resins bind to bile acids in the intestine and inhibit their re-absorption. Bile acids are derived from cholesterol and when they are attached to resins, they are not reabsorbed and secreted through stools.
HMG-CoA reductase inhibitor or Statins inhibit the enzyme HMG-CoA reductase. This enzyme is crucial for synthesis of cholesterol through mevalonic acid pathway. Therefore, by inhibiting this enzyme, cholesterol synthesis can be prevented in the body.
Fibric acid derivatives: Although the clear mechanism of action is not established, fibric acid derivatives presume to inhibit cholesterol synthesis and lower low density lipoproteins.
Nicotinic acid (Niacin, Vit B) involves in tissue oxidation and reduction reactions that decreases liver low density lipoproteins and very low density lipoproteins production. Niacin also inhibits the lypolysis.
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