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The term high cholesterol is a bit misleading, because there are two types of cholesterol. If you've been told you have high cholesterol, it usually means you have more of the bad type and less of the good type. This may put you at higher risk of having a heart attack or a stroke.

You won't notice if you have too much bad cholesterol, because you won't have any symptoms. The only way you can find out is to have a blood test.

• There are two main kinds of cholesterol: good cholesterol (HDL cholesterol) and bad cholesterol (LDL cholesterol).
• Eating saturated fats and trans fats can increase the amount of bad cholesterol in your blood. Saturated fats are found in foods such as meat, butter and cream. Trans fats are found in cookies, cakes, pastries and fast food.
• Too much bad cholesterol won't cause any symptoms, but it can increase your risk of having a heart attack or a stroke.
• You can lower your bad cholesterol by changing what you eat, taking medicines or both. This will lower your risk of having a heart attack or a stroke.
• If you smoke, stopping smoking can increase the amount of good cholesterol in your blood, which can lower your risk of having a heart attack or stroke.

Cholesterol is a fatty substance that is found in every cell in your body. Only a small amount of the cholesterol in your body comes directly from food. Most is made in your liver from saturated fats that you eat.

We've all started to think that fats are bad for us, but the body needs some fats to work properly. For example, fats are a source of energy and some vitamins.

There are several different types of fat in the food we eat.

Saturated fats are found in meat, butter and other dairy products. Your liver turns saturated fats into cholesterol. So if you want to lower your cholesterol level, you need to eat less saturated fat.

Unsaturated fats are divided into polyunsaturated and monounsaturated. They are found in vegetable oil and olive oil.

Omega-3 fatty acids are a type of polyunsaturated fat. They are found mainly in oily fish such as mackerel, salmon, sardines and herring, and fresh (but not canned) tuna. They can help make the blood less sticky and reduce the chances of a clot forming, which can lead to a heart attack. Other "good" unsaturated fats are found in leafy green vegetables, vegetable oils and margarine.

Trans fats are solid fats found in cookies, cakes, pastries and fast food. Scientists think that your body handles these fats in the same way as saturated fats. So if you want to lower your cholesterol you need to eat fewer trans fats.

You don't need to know what these names mean. All you need to remember is that saturated fats and trans fats may be harmful. Eating these tends to increase the amount of bad cholesterol in your blood.

To learn more, see A guide to fats in food and More about cholesterol and triglycerides.

Cholesterol can't travel around the body by itself. It has to link up with other substances in the body called proteins to form particles called lipoproteins. There are several different types of lipoproteins in your blood. The two most important are called LDL and HDL.

• Low-density lipoprotein (LDL): This moves cholesterol from your liver and through your blood to your body's cells. LDL cholesterol is called bad cholesterol. This is because it can build up in your blood vessels and this increases your risk of getting heart disease. The more LDL cholesterol there is in your blood, the greater your risk of getting heart disease. When doctors say you have high cholesterol, they mean you have a lot of bad (LDL) cholesterol in your blood.
• High-density lipoprotein (HDL): This picks up any extra cholesterol from your body and takes it back to your liver. Because it clears cholesterol from your blood, it's often called good cholesterol. The more good (HDL) cholesterol you have in your blood, the lower your risk of heart disease.

If you have high cholesterol it means that the level of cholesterol in your blood is outside of the normal range. For example, you may have too much bad (LDL) cholesterol and not enough good (HDL) cholesterol.

If you have too much bad cholesterol in your blood it builds up to form fatty deposits or plaques along the inside of the blood vessels. These plaques clog up the blood vessels, making them narrower. This condition is called atherosclerosis. It is harder for blood to flow through narrowed blood vessels and this puts you at increased risk of heart disease.

Sometimes the plaques make the walls of the blood vessels bumpy. This can lead to blood clots forming inside them. When a blood clot forms on a plaque, it can block the flow of blood to your heart or brain and this can cause a heart attack or a stroke.

To learn more, see What is a stroke?

The types of fats that you have to worry about the most are saturated fats and trans fats. These are the solid fats found in meat and meat products (such as hotdogs and hamburgers), and in dairy products (such as butter, hard cheese, milk and cream). If you eat too much of this type of fat, the amount of bad (or LDL) cholesterol in your blood rises.¹

Some people are more likely to get high cholesterol than others. The things that raise your chances of getting a condition are called risk factors. You can control some of the risk factors for high cholesterol, such as your diet, but you can't control others, such as your family history.

For more information, see Risk factors for high cholesterol.

When doctors talk about risk factors for heart disease, they are talking about the things that raise your chances of having a heart attack or a stroke. Having a high level of bad cholesterol is not the only risk factor for heart disease. Other things count, too, especially your age, blood pressure, whether or not you have diabetes and whether or not you smoke. Your doctor will consider these before deciding whether you should have a cholesterol test to see whether you need treatment.

For example, if your level of bad (LDL) cholesterol is slightly high, but you have no other risk factors for heart disease, your doctor will probably not worry too much. He or she may give you some advice about what you eat and check your cholesterol again after a few months. But you probably won't need drug treatment.

On the other hand, if you have low levels of good (HDL) cholesterol and high levels of bad (LDL) cholesterol, as well as high blood pressure and diabetes, then your doctor may consider drug treatment.

Many people who have too much bad cholesterol in their blood also have too much triglyceride in their blood. Triglycerides are another type of fat in the blood. High levels of triglycerides can be harmful. But it's not clear how triglycerides might cause heart disease. For the past 30 years, doctors have been arguing over whether or not triglycerides are important in causing heart disease.

But most doctors now agree that there is more and more evidence that having a lot of triglycerides in the blood raises your chance of getting narrowing of the arteries (atherosclerosis) and heart disease.^{2 3 4 5 6}