What is cholesterol?

Cholesterol is a fatty substance which is made in the liver. 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.

See how you can get a cholesterol test 

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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

Where is cholesterol made?

Some of our cholesterol comes from the food we eat, but most (about 80%) is made in the liver in a complex 37-step process. 

Cholesterol and another type of blood fat called triglycerides cannot circulate loosely in the blood, so the liver packages them into  “parcels” called lipoproteins.

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

How is it broken down?

Once in the blood stream, 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 – bile acids break down the fats in food.

A small amount of bile acids will be removed from the body as a waste product in your poo. 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. The liver has to take more cholesterol out of the blood to make more bile, lowering your cholesterol levels.

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

Learn more about what raises your cholesterol


  • saturated fats
  • low activity
  • genetic conditions

What are triglycerides?

There is another type of blood fat called triglycerides.

Triglycerides enter the blood stream after a meal. Some are also made by your liver. Triglycerides are packaged into lipoproteins along with cholesterol. When they reach the cells throughout your body, the triglycerides are used for energy or stored for later.

A high triglyceride level in your blood should be investigated by your GP. There can be many reasons for a high triglyceride level and it's important to find out the exact cause. Raised triglycerides can add to your overall risk of developing heart disease, and if they're very high, they can cause other serious problems such as pancreatitis. 

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

Read more about triglycerides and what can raise them


What are the different types of cholesterol?

Cholesterol is a type of blood fat, and blood fats are known as lipids. Cholesterol and other lipids are carried in the blood attached to proteins, forming tiny spheres, or "parcels" known as lipoproteins. So, lipoproteins are 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 cholesterol (low density lipoprotein)
    This is often called bad cholesterol, because too much in the blood can lead to health problems. These lipoproteins contain lots of cholesterol. Their job is to deliver cholesterol to the cells where it’s needed. But if there’s too much LDL cholesterol in your blood it can build up in the arteries, clogging them up.
  • HDL cholesterol (high density lipoprotein)
    This is often called good cholesterol because it helps prevent disease. They contain lots of protein, and very little cholesterol. 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 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, fat can be laid down in your artery walls, clogging them up. 
  • IDL (Intermediate density lipoproteins)
    These lipoproteins also carry cholesterol and triglycerides. They are in fact VLDL lipoproteins – after some of the triglycerides have been taken out of them. They sit between VLDL and LDL cholesterol in terms of how much fat they carry. 
  • Chylomicrons
    These are the largest lipoprotein. They carry triglycerides from the gut to the liver after a meal. They are broken down in the liver and the fats are repackaged into the other lipoproteins.


Learn how cholesterol levels differ for men and women

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