MRC/BHF Heart Protection Study

Questions and Answers about Cholesterol

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Questions and Answers about Cholesterol

QWhat is cholesterol?
AA type of fat, called a lipid, that is present in the blood and in all the cell membranes.
QWhere does cholesterol come from?
AIt is mainly made in the body, manufactured in the liver from a variety of foods, but mostly from saturated fats. Not much cholesterol is found in foods except for eggs, liver and kidneys.
QWhat is cholesterol's role in the body?
A It plays an important part in the functioning of every cell wall throughout the body so needs to be transported around the body. It is the material that the body uses to make other vital substances, including certain hormones.
QHow does it do that?
ABoth cholesterol and fats (triglycerides) travel around the body in particles associated with proteins. These are referred to as lipoprotein particles.
QWhat are lipoproteins?
AThese are particles with a core made up of cholesterol and triglycerides in varying proportions, and an outer wrapping of phospholipids and apolipoproteins (carrier proteins).
QAre all lipoproteins the same?
ANo. There are two main forms
  • low density lipoproteins (LDL) - often referred to as 'bad' cholesterol - which carry cholesterol from the liver to the cells, and have apolipoprotein B carrier proteins on their surface.
  • high density lipoproteins (HDL) - often referred to as 'good' cholesterol - which return excess cholesterol to the liver, and have apolipoprotein A carrier proteins on their surface.
QWhat are blood lipids?
AThis is the collective name for all the fatty substances in the blood, including HDL cholesterol, LDL cholesterol and triglycerides.
QWhat is the role of cholesterol in coronary heart disease (CHD)?
A CHD is caused when the blood vessels to the heart - the coronary arteries - become narrowed or 'furred up' by a gradual build-up of a fatty coating on the inside walls. This condition is called atherosclerosis. The fatty coating is called atheroma.
Q How does this process happen?
AAtheroma develops when LDL cholesterol undergoes a chemical process known as oxidation and is taken up by cells in the coronary artery walls, starting the narrowing process. But HDL cholesterol removes cholesterol from the circulation, thus protecting against CHD. So the balance between the two substances is vital, and individuals have least CHD with a high level of HDL and a low level of LDL in the blood (which can also be assessed by measuring the levels of apolipoprotein A and B).
QWhat factors influence this balance?
AA person's intake of fats is important - not only the total fat intake, but also the type of fat intake. The level of LDL cholesterol in the blood tends to rise when increasing amounts of saturated fats are eaten. But unsaturated fats, in particular polyunsaturated fats, have a beneficial effect as they tend to lower LDL.
QWhat causes high 'bad' cholesterol levels?
ASome people can have high LDL levels because of disease, such as an under-active thyroid gland or chronic renal failure. One person in 500 has high levels because of an inherited disorder called familial hypercholesterolaemia (FH) in which the mechanism that removes LDL cholesterol from the blood does not work efficiently. But, the most common cause of high blood cholesterol levels is too much saturated fat in the diet.
QHow is blood cholesterol measured?
ABy a blood test. This measures the level in units called millimoles per litre of blood, usually shortened to mmol/l. Levels can vary in an individual from day to day or at different times of the day. So, normally a series of readings is taken and the average used. In the USA they measure cholesterol in milligrams per decilitre which is shortened to mg/dl. A cholesterol level of 5 mmol/l is approximately equal to 200mg/dl. (N.B. The mmol/l of total or LDL cholesterol can be converted to mg/dl approximately by multiplying by 40).
QWhat is the mean blood cholesterol level?
A The mean blood cholesterol level for people aged 16 and above in the UK is about 5.5mmol/l, and about one-fifth have total blood cholesterol levels above 6.5mmol/l. This average of about 5.5mmol/l for total cholesterol typically reflects LDL cholesterol levels of about 3.5 to 4.0 and HDL cholesterol levels of about 1.0 (with the remainder being other lipid particles). In China (where there is much less heart disease), mean total cholesterol levels in the cities are about 4.5mmol/l for men and women aged 35-64 (with lower levels in the countryside), and only about one-fifth have levels higher than 5.2mmol/l.
QWhy does it matter if blood cholesterol levels are high?
A Because it increases the risk of coronary heart disease - it is one of the most important risk factors. In general, the higher your cholesterol level, the higher your risk of heart disease. (Other risk factors for heart disease are smoking, high blood pressure, lack of physical activity and obesity.) Heart attack risk also increases if you are diabetic, have familial hypercholesterolaemia, have already had a heart attack, angina or a stroke, or have circulatory problems in the legs. The more of these risk factors a person accumulates, the higher is the risk of a heart attack.
QHow can you lower blood cholesterol levels?
A A healthier diet (including replacing bad fats by good fats and being more active) is a good start. But you may need medication. If so, the likeliest drugs to be prescribed will be long-term treatment with statins - the subject, together with antioxidant vitamins, of the MRC/BHF Heart Protection Study. See also background information on statins and antioxidants.