What is cholesterol?

Cholesterol is a fatty substance which is made in the liver and it’s found in some foods too. We all need some cholesterol in our bodies just to keep us ticking over but having too much can clog up your arteries and lead to health problems in the future.

By getting a simple cholesterol test and making positive lifestyle changes, most people can keep their cholesterol levels healthy.

Why do we need cholesterol?

Cholesterol plays a vital role in how your body works. There is cholesterol in every cell in your body, and it's especially important in your brain, nerves and skin.

Cholesterol has three main jobs:

  • It’s part of the outer layer, or membrane, of all your body’s cells
  • It’s used to make vitamin D and steroid hormones which keep your bones, teeth and muscles healthy
  • It’s used to make bile, which helps to digest the fats you eat

What are the different types of cholesterol?

Cholesterol is a type of blood fat – blood fats are known as lipids. Cholesterol is carried in the blood from the liver, where it’s made, to wherever it’s needed in the body. It’s carried attached to proteins and other fats, and together they form tiny spheres, or balls, known as lipoproteins – lipids plus proteins.

There are two main types of lipoproteins. When people talk about the different types of cholesterol, they’re usually talking about these lipoproteins.

  • LDL (low density lipoprotein)
    This is often called bad cholesterol, because too much in the blood can lead to health problems. They contain lots of fat. LDL cholesterols’ job is to deliver cholesterol to the cells where it’s needed. But if there’s too much it can start to build up in the arteries, clogging them up.
  • HDL (high density lipoprotein)
    This is often called good cholesterol because it helps your body stay healthy and prevents disease. They contain lots of protein, and very little fat. HDL cholesterol’s job is to carry cholesterol away from the cells, back to the liver, where it can be broken down and removed from the body.


There are other types of lipoproteins too.

  • VLDL (very low density lipoproteins)
    These are larger. They carry another type of fat called triglycerides, plus some cholesterol, from the liver around your body. They contain lots of fat and very little protein. If there is too much VLDL in your blood it can be laid down in your artery walls.
  • IDL (Intermediate density lipoproteins)
    These carry cholesterol and triglycerides.
  • Chylomicrons
    These are the largest lipoprotein. They carry triglycerides from the gut to the liver after a meal, where they are broken down and the fats are repackaged into the other lipoproteins.



There is another type of blood fat called triglycerides.

Triglycerides enter the blood stream after a meal, and normally your liver will clear them out of your blood. Triglycerides are packaged into lipoproteins in the liver, along with cholesterol. When they reach the cells throughout your body, they’re used for energy or stored for later.

A high triglyceride level in your blood can be a sign that fat has built up in your liver, and the liver can't clear fat from your blood as it should. This puts you at risk of developing liver disease. 

Fat can also build up in the pancreas, leading to type 2 diabetes, and in the heart, leading to heart disease.

A high triglyceride level can be caused by carrying too much weight around your middle. An unhealthy diet and lifestyle, your genes, and other illnesses can also lead to high triglycerides.

It is useful to have your triglycerides tested when you get a cholesterol check.

Read more about triglycerides on our factsheet.

How is cholesterol made?

Some of our cholesterol comes from the food we eat; but most is made in the liver.

After a meal, the fat in your food is broken down into triglycerides. Triglycerides from our food are absorbed in the intestines and transported around the body. Cholesterol and triglycerides cannot circulate loosely in the blood, so they are transported in “parcels” called lipoproteins.

The lipoproteins are then released into the blood and carried around the body to wherever they're needed.

How is cholesterol broken down?

Some cholesterol will be returned to the liver and broken down. It’s used to make bile acids which are released into the intestines to help with digestion, they break down fats in food.

A small amount of bile acids will be removed from the body as a waste product. But most will be absorbed back into the blood, returned to the liver and used again for digestion.

Some treatments for high cholesterol work by stopping bile from being absorbed back into the blood. So, the liver has to take more cholesterol out of the blood to make more bile, lowering your cholesterol levels.

What raises your cholesterol?

Your blood fats – that is, your cholesterol and triglycerides – can become raised for a number of reasons.

For example:

  • a diet which is high in saturated fats
  • not being active enough, so the fats aren't used up for energy
  • genetic conditions which mean the fats aren't processed in the usual way.

What if I have high cholesterol?

  • saturated fats
  • low activity
  • genetic conditions

Why should I get a cholesterol test?

High cholesterol usually doesn’t have any symptoms, so you won’t know if you have it. The first sign of it can be a heart attack.

There are different causes of high cholesterol – it can be to do with your lifestyle, but it can be genetic too. So even if you are young, fit, slim and otherwise healthy you could still have high cholesterol.

A simple blood test can show you how much of the different types of cholesterol you have in your blood. This can give an idea of your risk of heart disease and stroke. It can show if you need to make any healthy changes or have any treatments to bring your cholesterol under control.

The blood test is very quick and easy. It's usually a finger prick test where you feel a tiny pinch as a small amount of blood is taken. Your doctor or nurse can check your cholesterol level there and then.