Cholesterol is a fatty substance in the body that is vital for the normal functioning of the body. It is predominantly made by the liver from the nutrients we eat, but can also be found in some food.

High level of cholesterol and lipids (fat) in your blood (hyperlipidaemia) can have a negative impact on your health. High cholesterol itself does not cause any symptoms, but it increases your risk of serious health conditions.

Types of cholesterol

Cholesterol is carried in your blood by proteins, and when the two combine they are called lipoproteins. There are harmful and protective lipoproteins known as, LDL 'bad' and HDL 'good' cholesterol.

  • Low-density lipoprotein (LDL): LDL carries cholesterol from your liver to the cells that need it. If there is too much cholesterol for the cells to use, levels of LDL can build up along the artery walls, leading to disease of the arteries, or atherosclerosis. For this reason, LDL cholesterol is known as "bad cholesterol".
  • High-density lipoprotein (HDL): HDL carries cholesterol away from the cells and back to the liver, where it is either broken down or passed out of the body as a waste product. For this reason, it is referred to as "good cholesterol".

The amount of cholesterol in the blood (both LDL and HDL) can be measured with a blood test. The recommended cholesterol levels in the blood vary between those with a higher or lower risk of developing arterial disease.

Causes of high cholesterol

There are several factors that may contribute to you having high cholesterol. These include:

  • having a diet high in saturated fat
  • a lack of exercise
  • being overweight or obese (having a body mass index (BMI) more than 25)
  • drinking more than the recommended daily amount of alcohol (this increases the level of triglycerides in your blood)
  • smoking
  • age and gender – your cholesterol levels generally rise with increasing age and can be affected by your gender

High cholesterol can sometimes be caused by a condition that runs in your family called familial hypercholesterolaemia (FH). In the UK, about one in 500 people have this condition. It is not caused by an unhealthy lifestyle but is passed through a family's genetics. However, the above lifestyle factors are still relevant risk factors for those with FH and maintaining a healthy diet and lifestyle is extremely important.

Other conditions, such as poorly controlled diabetes, certain kidney and liver diseases and underactive thyroid (hypothyroidism) may also cause your levels of cholesterol or triglycerides to be high. Some medicines such as the oral contraceptive pill, beta-blockers, steroids or thiazides (a type of diuretic) may also affect your blood lipid levels.