Cholesterol is a fat-like substance which cannot travel in the blood on its own and so it must group with special proteins to form a lipoprotein. The main groups of lipoproteins based mainly on their different sizes and density are: high-density lipoproteins (HDL), low-density lipoproteins (LDL), very low-density lipoproteins (VLDL). Each group has a different function in the body. The majority of cholesterol is actually produced in the body by the liver but it is also consumed via the diet in animal products such as eggs, meat and dairy. The body uses cholesterol usefully to manufacture hormones, make vitamin D, build cell walls, and create bile salts that are needed to digest fat. Cholesterol is therefore an important molecule, though too much cholesterol may cause fat to build up in the walls of the larger arteries, leading to plaque formation. Otherwise known as atherosclerosis, this can cause narrowing of the arteries, leading to heart attacks and strokes. LDLs are produced by the liver and carry cholesterol and other fats from the liver to the different areas of the body, like muscles, tissues, organs, and the heart. If levels of LDL are high then this is an indication that there is an excess which then has the ability to stick to blood vessels, causing plaque build up. LDL is therefore known as “bad cholesterol”. VLDLs are another type of lipoprotein that carry cholesterol and triglyceride from the liver to organs and tissues in the body. VLDLs can become LDLs, and are also associated with atherosclerosis and heart disease. In contrast, HDL is known as “good cholesterol”. Rich in protein, it also carries cholesterol away from the cells and back to the liver, where it is broken down ready to be excreted from the body. Most importantly, HDL can actually remove cholesterol from plaques that have built up on artery walls, also helping to lower the risk of heart disease. High levels of HDL cholesterol are therefore beneficial; ideally the amount of HDL should be more than 20% of total cholesterol, which should be less than 5mm/L.
|Level mg/dL||Level mmol/L|
|Lower risk for heart disease|
|200–240||5.2–6.2||Borderline high risk|
|> 240||>6.2||>High risk|
Figure 1: Total cholesterol levels and risk of heart disease.