Cholesterol


Cholesterol is a soft, wax-like substance which is found in every cell in our body. It has an important role as it is part of the walls or membranes of each cell. It is also a key component in the manufacture of hormones (chemical messengers in our body) and bile acids which work in our intestines to help promote the absorption of fat from our diets.

Cholesterol and fats do not dissolve in the blood and thus they are bound to special proteins called apoproteins which keep the cholesterol and fat soluble. The complex of fats, cholesterol and apoproteins is called a lipoprotein. There are many different lipoprotein particles in the blood stream which differ in their size and composition of fats and proteins. The largest lipoprotein is called a chylomicron which is produced in the intestinal cells. These lipoproteins help to deliver dietary fat to the liver. The liver then in turn produces very low density lipoproteins (VLDL) which are gradually broken down to form low-density lipoproteins (LDL). During this breakdown process fragments are released which join other apoproteins produced in the liver to form high density lipoproteins (HDL). Whereas VLDL and LDL deliver cholesterol and fat to all our cells, HDL is thought to be responsible for transporting cholesterol back from our cells to the liver where it is sent into the intestine for excretion.

Normally, if the transport system was working well like smooth running traffic, there would be no large build up of lipoprotein particles in the blood stream. However, due to genetic abnormalities in our lipoprotein particles or in the receptors on cells which help clear these particles, there are potential road blocks in the system. If we then increase the amount of lipoprotein particles in the blood stream by eating a high fat diet, we basically increase the number of vehicles on the roads and if genetic road blocks exist, then there will be lipoprotein traffic congestion. When there is excess amounts of LDL particles we get the condition known as hypercholesterolaemia. High LDL cholesterol levels are a major risk factor for damaging the coronary arteries which may lead to a heart attack.

What is LDL cholesterol?
Low density lipoprotein (LDL)particles are the main ones involved in carrying cholesterol in the blood. LDL delivers its cholesterol to all body cells by binding to a receptor on the surface of cells called amazingly the "LDL receptor". When one has too much LDL cholesterol floating around in the blood stream, it can slowly build up within the inner walls of the arteries. The arteries supplying blood to the heart and brain are most often affected. When LDL levels are high especially in someone who smokes, has high blood pressure or diabetes, the build up in the arteries grows quicker to form plaques. These plaques are thick deposits which can be both hard and soft and can clog up the arteries. This condition is known as atherosclerosis (which means hard porridge because of how these plaques look inside the arteries). If one of these plaques tears, a clot (or thrombus) may form on the plaque which can block the flow of blood to part of the heart muscle and cause a heart attack. If a clot blocks the flow of blood to part of the brain, the result is a stroke. Therefore having a high level of LDL cholesterol in the blood stream is a bad thing. A quick way to remember that LDL is the bad cholesterol is L for LDL , L for "Lousy cholesterol"

What is HDL cholesterol?
High-density Lipoproteins are considered by many researchers to be responsible for transporting cholesterol back from cells to the liver for removal from the body. Depending on the individual, about one-fourth of blood cholesterol is carried by HDL. HDL may also remove excess cholesterol from atherosclerotic plaques and thus slow down the growth of plaques. HDL is known as "good" cholesterol because a high level of HDL seems to protect against heart attack, whereas a low HDL level offers less protection from heart disease. A quick way to remember that HDL is the good cholesterol is H for HDL , H for "Healthy cholesterol"

What is Lp(a) cholesterol?
Lp(a) is a cholesterol carrying particle that looks very like LDL but additionally it carries a small protein called apo(a). The level of Lp(a) in our bodies is genetically determined. High levels are associated with an increased risk of heart disease particularly when LDL cholesterol levels are also high. Because Lp(a) also has effects in promoting clot formation, it is considered an important risk factor for heart disease.

How does exercise affect cholesterol ?
Exercise has a number of beneficial effects on cholesterol and blood fats (triglycerides). Regular exercise is associated with an increased ability to clear fat particles from the blood stream after meals. This is because the exercised muscles need more energy from fat and thus utilize the fat quickly so that it is cleared from the blood stream. Exercise also affects blood cholesterol levels by increasing HDL levels ("healthy" cholesterol). A higher HDL level is linked with decreased risk of heart disease. Long term exercise programs may also reduce LDL cholesterol levels. It has been established that exercise can also help control weight, diabetes, and high blood pressure all of which would reduce the risk of heart disease.

Not taking exercise is now accepted as a major risk factor for heart disease. Even mild activities, if done daily, help reduce your risk. Examples are walking for pleasure (see Sli na Slainte), gardening, housework, aerobics and dancing.

Smoking and cholesterol ?
Among the many harmful affects of cigarette smoking is the fact that it can lower the level of the healthy HDL cholesterol. Smoking also increases the potential to oxidise lipoprotein particles which is a damaged form of lipoproteins which really increases oneís risk of heart disease.

How does alcohol affect cholesterol?
In some studies, moderate use of alcohol is linked with higher HDL or "healthy" cholesterol levels. However, the benefit is not great enough to recommend drinking alcohol if you donít do so already.

If you drink, do so in moderation. Incidence of heart disease in those who consume moderate amounts of alcohol (an average of one to two drinks per day for men and one drink per day for women) is lower than in non-drinkers. However, with increased consumption of alcohol, there are increased public health dangers, such as alcoholism, high blood pressure, obesity, stroke, suicide, etc. We would therefore not recommend individuals to start drinking to reduce their risk of heart disease. It is best to consult your doctor for advice on consuming alcohol in moderation (no more than 2 drinks per day).


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