Why cholesterol matters

It is often derided as a health baddie but the fatty substance called cholesterol is actually essential for making cell membranes, hormones and bile salts. High levels are associated with a higher risk of coronary artery disease due to hardening of the arteries - a condition known as atherosclerosis - and it is believed that around 70 per cent of adults in the UK have a blood level of cholesterol high enough to be a health risk.

What is it?
Cholesterol belongs to a chemical family called lipids, which are found in cell membranes throughout the body. Lipids, including fat and triglycerides, are also used to produce hormones, vitamin D and the bile acids that aid the digestion of fat. But you don't need to worry about getting enough in your diet, as the body is able to meet its needs by producing cholesterol in the liver.

The good and the bad
Not all cholesterol is bad. It is transported around the body in three forms known as 'lipoproteins.'

• LDL or low-density lipoprotein. Often called 'bad' cholesterol, because too much can lead to cholesterol build-up and blockage in the arteries. LDL cholesterol carries most of the cholesterol in the blood.
  
• HDL or high-density lipoprotein, or 'good' cholesterol, helps transport cholesterol from other parts of the body to the liver. This helps remove it from the body, therefore preventing it from piling up in the arteries.
  
• A third type of lipoprotein, which is very low in density, transports triglycerides in the blood; high levels of triglycerides have also been linked to increased risk of heart disease.

Cholesterol and hardening of the arteries
The level of cholesterol in the blood increases as we eat more amounts of saturated fats. Most people with high cholesterol have a diet rich in whole-milk dairy products, eggs, animal fats or meat. If extra cholesterol and fat in the blood undergo a chemical reaction called oxidation, they are taken up by scavenger cells which, when over-laden, become trapped and are deposited in the inner walls of the arteries that supply blood to the heart. These deposits make the arteries narrower and narrower, contributing to atherosclerosis and, if unchecked, coronary heart disease. Eating plenty of fruit and vegetables supplies substances called antioxidants which protect circulating cholesterol from oxidation, and lowers the risk of atherosclerosis.