What is cholesterol?
Cholesterol is an insoluble fatty substance that is needed by the body for many functions, such as building cell membranes, producing certain hormones and transporting fat soluble vitamins around the body. It is made in the liver and also obtained from the diet. Cholesterol is transported in the blood along with triglycerides, which is another type of fat. Since cholesterol is not soluble in blood it is carried to and from the liver by lipoproteins. These include low density lipoproteins (LDL) known as “bad” cholesterol because they carry cholesterol from the liver and deposit excess in the arteries. High density lipoproteins (HDL) carry cholesterol back to the liver and are therefore called “good” cholesterol.
High cholesterol and atherosclerosisIf there is more cholesterol in the blood than the body needs, it becomes deposited in the artery walls where it can build up, blocking the arteries and causing hardened areas called plaques, which increases risk of heart disease. This condition is known as atherosclerosis. High cholesterol in the blood and other fats (triglycerides) is known as hypercholesterolaemia and this condition is usually due to lifestyle, including high-fat diet, obesity and lack of exercise, but it can be inherited. The ratio of total cholesterol over HDL (good cholesterol) is also an important consideration.
Cholesterol lowering medicationsCholesterol lowering medications are available to treat hypercholesterolaemia in people who have not responded to a low-fat diet and lifestyle changes alone; also for those with an inherited condition and who cannot lower cholesterol levels by lifestyle changes alone. They include:
- Statins that block the production of cholesterol by the liver, by inhibiting the action of the enzyme HMG-CoA reductase that plays an important role in cholesterol synthesis. Statins only block cholesterol produced in the liver but have no effect on cholesterol that comes from fat in the diet. Several statins are available including, atorvastatin, simvastatin, pravastatin and rosuvastatin.
- Cholesterol absorption inhibitors, like ezetimibe act directly on the small intestine wall to block the action of the sterol transporter in the intestine wall. This action inhibits intestinal absorption of cholesterol from the diet and reduces cholesterol stores in the liver, which helps lower blood cholesterol levels.
- Fibrates like fenofibrate activate the enzyme Peroxisome Proliferator Activated Receptor type alpha (PPARα) that regulates the production of another enzyme involved in the breakdown of lipids in the blood. It also reduces the production of proteins that transport LDL lipids but increases the production of proteins that transport HDL. The overall effect is to lower triglycerides, total cholesterol, and LDL (bad) cholesterol, and increase HDL (good) cholesterol.