What is cholesterol?

Cholesterol is a type of blood fat 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, including heart disease.

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

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Why do we need cholesterol?

There is cholesterol in every cell in your body. It plays vital roles in how your body works, 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 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 is LDL cholesterol?

There are different types of cholesterol which have different effects in the body. You might hear your healthcare professional talk about LDL cholesterol and HDL cholesterol, which are the two main types.

LDL cholesterol

LDL cholesterol is often called ‘bad cholesterol’ because too much of it can clog up your arteries and lead to health problems later on, such as heart disease, heart attacks and strokes. You do need some LDL cholesterol in your blood. It’s when there’s too much that it’s a problem.

HDL cholesterol

HDL cholesterol is often called ‘good cholesterol’ because it carries cholesterol away from your cells, back to your liver to be broken down. So, it helps prevent disease.

Read more about the types of cholesterol

Where is cholesterol made?

Some 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 can't circulate loosely in the blood, so the liver packages them into  “parcels” called lipoproteins, including LDL and HDL cholesterol. 

They are released into the blood to carry the fats around the body to wherever they're needed. 

How is it broken down?

Once in the blood stream, some cholesterol will be carried back to the liver and broken down. The liver uses cholesterol to make bile acids which are released into the intestines to help with digestion. They break down the fats in food.

A small amount of bile acids will leave 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.

What raises your cholesterol?

Your cholesterol and triglycerides can become raised for a number of reasons. For example:

Learn more about what raises your cholesterol

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What are tryglycerides?

Triglycerides are another type of blood fat. Most triglycerides enter the blood stream after a meal, and some are also made by your liver.

Triglycerides are packaged into lipoproteins along with cholesterol. When they reach the cells throughout your body, they are used for energy or stored for later.

It's useful to have your triglycerides tested when you get a cholesterol check. A high triglyceride level should be investigated by your GP. There can be many reasons for raised triglycerides and it's important to find out the exact cause. Raised triglycerides can add to your risk of developing heart disease, and if they're very high, they can cause other serious problems such as pancreatitis. 

Read more about triglycerides and what can raise them

What are  lipoproteins?

Cholesterol is a type of fat, and fats can’t travel in the blood on their own. They need to be attached to proteins.

Lipoproteins are little parcels made of fats and proteins that carry fats around the body. Lipid is another name for fat, so ‘lipoprotein’ means fat plus protein.

LDL cholesterol and HDL cholesterol are the two main types of lipoprotein, but there are other types too. They are named according to how ‘dense’ they are. Protein is heavy. So, lipoproteins that contain more protein are more heavy or ‘high density’. Those that contain less protein and more fat are ‘low density’. 

  • LDL cholesterol (low density lipoprotein)
    These lipoproteins contain lots of cholesterol so they are ‘low density’. Their job is to deliver cholesterol to the cells where it’s needed. If there is too much LDL in the blood, cholesterol can fur up the blood vessel walls, clogging them up, so it’s sometimes called ‘bad cholesterol’.
  • HDL cholesterol (high density lipoprotein)
    These contain lots of protein and very little cholesterol. So they are ‘high density’. They carry cholesterol away from the cells and back to the liver, which removes the cholesterol from the body.  HDL cholesterol is sometimes called good cholesterol because it can help prevent disease.
  • VLDL (very low density lipoproteins)
    These are larger and contain lots of fat and very little protein, so they are very low density. They carry triglycerides and some cholesterol from the liver around your body. Like LDL cholesterol, too much VLDL cholesterol in your blood means fat can be laid down in your artery walls, clogging them up.
  • IDL (Intermediate density lipoproteins)
    These also carry cholesterol and triglycerides. They are 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.