Cholesterol is a sterol (a chemical precursor of natural steroids). It’s an important part of a healthy body, being a building block for steroids such as the sex hormones produced in the gonads and the hormones of the adrenal cortex. It is also the basis of the body’s manufacture of bile salts.

It’s also used to form cell membranes and other needed tissues. It’s made in the body, mainly in the liver. The amount of cholesterol present in the blood ranges from 3.6 to 7.8 mmol/litre. A level above 6 mmol/litre is regarded as high, and is a risk factor for arterial disease.

Scientists have found two forms of cholesterol-carrying proteins in the blood: high-density and low-density lipoproteins. The low-density form is thought to promote arterial disease, whereas the high-density component may oppose it.

People who naturally have abnormally high levels of cholesterol (especially low-density lipoproteins) can reduce their risk of heart attack by lowering their blood cholesterol. This can be done by following a diet low in saturated fats (and by using cholesterol-lowering drugs).

The recommended average daily cholesterol intake is up to 300 milligrams. Research has shown that a diet rich in animal fats tends to raise the levels of cholesterol and the related fats and lipids in the blood.

Cholesterol is found in foods that come from animals, such as:

• Meats
• Poultry
• Fish
• Seafood
• Dairy products.

Foods from plants (fruits, vegetables, grains, nuts and seeds) do not contain cholesterol.

When saturated solid fats are added to the diet, the amount of cholesterol in the blood increases, but when liquid, unsaturated fats or oils (particularly the polyunsaturated type) replace solid fats in the diet, the amount of cholesterol decreases. Foods high in unsaturated fats include olive oil and oily fish.

Evidence strongly indicates that people with high cholesterol levels are more likely to develop atherosclerosis (also called arteriosclerosis), heart attacks and strokes than are people with lower levels. The risk of coronary heart disease rises as blood cholesterol levels increase. When other risk factors (such as high blood pressure and cigarette smoking) are present, this risk increases even more.

In atherosclerosis, plaques containing cholesterol are deposited on the walls of arteries, particularly those of small and medium size, reducing their inside diameter and the flow of blood. Clotting of blood (such as happens in the coronary arteries during a heart attack) is most likely to develop where arterial walls are roughened by such plaques.

The increase in the West in atherosclerosis and related heart disease and other conditions, such as diabetes mellitus, has focused research on a possible link between these diseases and high blood cholesterol, and between high blood cholesterol and the amount of fat in the diet. Current thinking is that the traditional Mediterranean diet, with its emphasis on raw olive oil in many foods and low animal-fat content, is one of the best there is for cardiovascular health (the health of the heart and blood circulation).

The most common cause is excess animal fat in the diet. Less often it is caused by genetic factors.

Treatment

Cholesterol-lowering drugs work in different ways. Cholesterol is made in the liver, and some drugs work here to reduce the amount it makes. Other treatments reduce absorption of cholesterol from food in the intestine.