Cholesterol is a fatty substance that is vital for the normal functioning of the body. But too much can cause it to build up in the arteries, restricting blood flow to the heart, brain and rest of the body. This raises the risk of angina, heart attacks, stroke and blood clots.

Cholesterol is made in the liver and is carried in the blood by proteins. The first - high-density lipoprotein (HDL) - carries cholesterol from cells to the liver where it is broken down or passed as waste. This is 'good cholesterol'. 'Bad cholesterol' - low-density lipoprotein (LDL) - carries cholesterol to cells, with excessive amounts that build into the artery walls.

High cholesterol can be genetic but it is also linked to a diet rich in saturated fat, as well as smoking, diabetes, high blood pressure and a family history of stroke or heart disease.

Blood cholesterol is measured in units called millimoles per litre of blood, often shortened to mmol/L. A healthy adult's overall level should be 5mmol/L or less, while their LDL level should be no more than 3mmol/L. An ideal level of HDL is above 1mmol/L.

Cholesterol can be lowered by eating a healthy, low-fat diet; not smoking, and exercising regularly. If these do not help, cholesterol-lowering medication like statins may be prescribed.

Source: UK - NHS