A LIPID that is an important constituent of body cells and is widely distributed throughout the body. It is especially abundant in the brain, nervous tissue, adrenal glands and skin. It is also found in egg yolk and gall-stones (see GALL-BLADDER, DISEASES OF). Cholesterol plays an important role in the body, being essential for the production of the sex hormones as well as for the repair of membranes. It is also the source from which BILE acids are manufactured. The total amount in the body of a man weighing 70 kilograms (10 stones) is around 140 grams, and the amount present in the blood is 3·6–7·8 mmol per litre (or 150–250 milligrams per 100 millilitres).

A high blood-cholesterol level – that is, one over 6 mmol per litre or 238 mg per 100 ml – is undesirable as there appears to be a correlation between a high blood cholesterol and ATHEROMA, the form of arterial degenerative disease associated with coronary thrombosis and high blood pressure. This is well exemplified in DIABETES MELLITUS and HYPOTHYROIDISM, two diseases in which there is a high blood cholesterol, sometimes going as high as 20 m.mol per litre; patients with these diseases are known to be particularly prone to arterial disease. There is also a familial disease known as hypercholesterolaemia, in which members of affected families have a blood cholesterol of around 18 m.mol per litre or more, and are particularly liable to premature degenerative disease of the arteries. Many experts believe that there is no ‘safe level’ and that everybody should attempt to keep their cholesterol level as low as possible.

Cholesterol exists in three forms in the blood: high-density lipoproteins (HDLs) which are believed to protect against arterial disease; a low-density version (LDLs); and a very low-density type (VLDLs) – these latter two being risk factors.

The rising incidence of arterial disease in Western countries in recent years has drawn attention to this relationship between high levels of cholesterol in the blood and arterial disease. The available evidence indicates that there is a relationship between blood-cholesterol levels and the amount of fat consumed; however, the blood-cholesterol level bears little relationship with the amount of cholesterol consumed, most of the cholesterol in the body being produced by the body itself.

On the other hand, diets high in saturated fatty acids – chiefly animal fats such as red meat, butter and dripping – tend to raise the blood-cholesterol level; while foods high in unsaturated fatty acids – chiefly vegetable products such as olive and sunflower oils, and oily fish such as mackerel and herring – tend to lower it. There is a tendency in Western society to eat too much animal fat, and current health recommendations are for everyone to decrease saturated-fat intake, increase unsaturated-fat intake, increase daily exercise, and avoid obesity. This advice is particularly important for people with high blood-cholesterol levels, with DIABETES MELLITUS, or with a history of coronary thrombosis (see HEART, DISEASES OF). As well as a low-cholesterol diet, people with high cholesterol values or arterial disease may be given cholesterol-reducing drugs such as STATINS.