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What is cholesterol?

Cholesterol in an egg

Cholesterol is a waxy substance, one of the wide range of fats (lipids) present in the body. It is essential to life.

Cholesterol is an important component of all cell membranes, with about 25% of the body’s total cholesterol in the cell membranes of the nervous system, where it is a major component of the fatty sheaths that insulate nerves.

It also provides the basic skeleton for the synthesis of many hormones – the sex steroids, such as oestrogen and testosterone, the steroid hormones made by the adrenal gland, for example cortisol, as well as for vitamin D.

Cholesterol is also essential for making bile acids and is therefore vital to digesting fats. An adult body contains about 150g of cholesterol.

How much cholesterol comes from the diet?

Although nearly all body tissues can make cholesterol, most is made by the liver and intestine. It is therefore naturally present in the blood, irrespective of how much cholesterol is consumed in the diet. The liver must produce a certain amount of cholesterol - without it the body would cease to function properly. It is estimated that an adult makes 0.5-1.0g of cholesterol per day, which is more than would usually be absorbed from the diet.

The total amount of cholesterol in our bodies at any one time will depend on the amounts made by the body, the amount of cholesterol absorbed from the diet and the amount eliminated from the body in the faeces. Usually only about one third of the cholesterol in the body comes from the diet.

In most people, the amount of cholesterol made by the body will decline when more is absorbed from the diet.

LDL and HDL cholesterol

Fats are mainly carried around the body attached to specialised proteins, the lipoproteins. These lipoproteins are constantly changing in composition as they deposit and receive fats from blood and body tissues and their chemistry and involvement in metabolism is complex.

In simple terms, most cholesterol in the blood (70%) is carried by low-density lipoproteins (LDL), which take cholesterol from the liver to body tissues. High blood levels of LDL-cholesterol (sometimes called "bad cholesterol") are associated with an increased risk of CHD. Much of the remaining cholesterol is carried as high-density lipoproteins (HDL), so-called "good cholesterol", which is involved in the disposal of cholesterol, and which is associated with a decreased risk of CHD.

CHD and cholesterol

Many factors influence the risk of cardiovascular disease, coronary heart disease (CHD) and stroke. These include non-modifiable factors such as inherited (genetic) risks (reflected in family history), increasing age and male gender, and the well-established modifiable risks such as smoking, raised blood pressure, elevated cholesterol levels, lack of physical activity, obesity and Type 2 diabetes.

Coronary heart disease can result in death when the blood supply to the heart is severely interrupted by a blockage of the coronary arteries which supply oxygen to the heart. There are two main parts of this process: the build-up of fatty plaques (atheroma) in the artery (atherosclerosis) and thrombosis – when some of the fatty material breaks away and causes a blood clot to form that blocks the artery.

A high level of cholesterol-rich LDL is believed to be one of several factors that contribute to build up of atheroma in the arteries.

All information checked by an independent Registered Nutritionist/Dietitian.