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Cholesterol - Health Information

Health Information

What is cholesterol

Cholesterol is a fatty substance which is found throughout the body and circulates in the bloodstream. It is vital to the normal functioning of the body and is an important constituent of body cells. It is an essential ingredient of vital body chemicals such as hormones produced by various glands e.g. the thyroid and ovaries. It is also a component of certain chemicals such as bile acids, which help in the natural digestive processes of fat taken in the diet.

How is cholesterol formed

Nearly all of the cholesterol in the body is manufactured by the liver, whilst a small amount is derived from the diet, formed from burning of foods which contain fat. This diet-derived fat is of two types, namely saturated and unsaturated.

The saturated form is found mainly in the following foods:

  • Meat and meat products (beef, lamb, pork, suet, lard dripping) derived from animal sources
  • Dairy products (milk, butter, cream, cheese)
  • Hard margarine and cooking fat
  • Cakes, biscuits, puddings, and chocolate

The unsaturated form is found in the following:

  • Vegetable oils
  • Soft margarine
  • Oily fish e.g. herring, mackerel, tuna, pilchards and sardines

The more saturated fats that are eaten the higher the blood cholesterol is likely to be, and therefore the higher the risk of developing coronary heart disease (as described later).

Cholesterol is transported around the body in the bloodstream by attachment to specific proteins, called lipoproteins, along with other small chemical substances derived from the breakdown of fat. These substances are known as triglycerides.

There are two types of lipoproteins each containing different amounts of protein and cholesterol. These are high density lipoprotein (HDL), which contains a high amount of protein and a relatively small amount of cholesterol, and low density lipoprotein (LDL) containing a smaller amount of protein and a high amount of cholesterol. These are the major cholesterol carrying substances and about 75% of the circulating cholesterol is carried in the form of LDL, whilst HDL's carry about 25% of the circulating cholesterol.

Why is high blood cholesterol important

If cholesterol is present in abnormally high quantities in the circulating blood, the body is unable to process this amount of fat and so excess cholesterol builds up in the body. It may be deposited in various parts of the body, especially on the walls of the arteries where it forms clumps, or plaques. These can severely narrow and eventually block off the blood supply in the arteries. This results in a loss of oxygen and glucose supply to tissues and muscles supplied by these arteries which can then become damaged.

The most important area where this build up can occur is in the coronary arteries. These form a network of blood vessels around the heart and if they are narrowed by becoming furred up with cholesterol deposits, then damage can occur to the heart muscle. This may take the form of angina or even a heart attack.

A similar problem can occur in the arteries in the legs, where impaired circulation can lead to pain on walking (called intermittent claudication) and if very severe can actually stop the circulation altogether.

A high level of HDL cholesterol is considered to be "good" in protecting against heart disease because it is not found in the body tissues and does not fur up the arteries. LDL cholesterol on the other hand, is found in body tissues and can be deposited in blood vessels. A high level of LDL type can therefore be regarded as a risk factor for the development of arterial disease.

There is no doubt that lowering of the blood cholesterol level will reduce the risk of developing coronary heart disease but the lowest cholesterol level which is desirable is, as yet, unknown.

When should it be measured

There are often no symptoms associated with high cholesterol and there is ongoing debates as to whether routine measurement should form part of the health screening examinations. There are however groups at risk, who should also be screened regularly:

  • Those with a family history in either parent or sibling of high cholesterol levels. The condition is likely to be inherited
  • Those patients who have a family history of premature (or early onset) heart disease, or high blood pressure
  • Those patients who are very overweight, who are smokers, or who themselves have suffered heart related symptoms. Along with high cholesterol, these constitute risk factors for coronary heart disease
  • Those who have other medical conditions such as alcohol problems diabetes, or kidney disease, all of which can be associated with a high blood cholesterol
  • patients who have received coronary artery bypass surgery

How is it measured

This involves a simple blood test. Cholesterol can be measured by means of an ordinary blood sample sent to the laboratory, or by a finger prick sample which is fed into a desk top analyser machine. Normally, there can be great variation in the level of cholesterol in a healthy, non-fasting person, so undue significance should not be given to a single reading of blood cholesterol. The family doctor or practice nurse will have more information about this.

The blood cholesterol and other fat components (such as triglycerides) are measured in units called millimoles per litre (mmol/l). A blood cholesterol below 4.5 mmol/l would be considered to be normal. Increasing levels ranging up to 8.0mmol/l and beyond, demand stricter dietary control and possibly tablets from the Gp. If a non-fasting (or "random") blood sample is found to be elevated, then a more accurate cholesterol level can be measured after having fasted for 10 hours. This will determine the LDL and HDL cholesterol levels and give a better idea of the risk of developing coronary disease.

What is the treatment

Treatment involves dietary modification and, where necessary, tablets to control obesity and reduce the cholesterol level.

Dietary control: Weight reduction, by avoiding dietary fat, will help reduce the cholesterol level. The following measures will aid in this:

  • Use skimmed or semi skimmed milk
  • Grill, bake or steam foods rather than fry them
  • Eat smaller portions of meat and trim off any fat
  • Eat low fat cheeses and margarine. Spread margarine and butter thinly
  • Do not add fat or oil in cooking
  • Make sure low fat foods are labelled "low in saturated fat" if a specific low cholesterol diet is required

Medication: These work by lowering the blood cholesterol, the triglyceride level, or both. There is now overwhelming evidence that lowering the blood cholesterol by diet and/or drugs will reduce the chances of patients suffering a heart attack. Cholesterol lowering tablets are not a substitute for a low fat diet. There are a number of groups of drugs:

  • Agents which bind bile acids in the bowel and interfere with absorption and digestion of fat and therefore reduce the amount of circulating cholesterol
  • The statins. These interfere with the production of cholesterol in the liver
  • The fibrates. Their main action is to reduce the triglyceride component

All these drugs work by lowering the blood cholesterol but each may be used appropriately in different circumstances.

Where can I get further information

Apart from contacting your Gp, the following organisations may be of further help:

British Heart Foundation
14 Fitzhardinge Street
London
W1H 4DH
Telephone: 020 7935 0185
Infoline: 08705 200656

Flora project for Heart Disease prevention
Van Den Bergh Foods
Brooke House
Manor Royal
Crawley
West Sussex
RH10 2RQ
Helpline: 0800 446464

Sources

  1. MONTAGUE, T., TSUYUKI, R., BURTON, J. et. al., (1994) prevention and regression of coronary atherosclerosis: is it safe and efficacious therapy Chest, 105(3) pp.718-26
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