What is cholesterol?
Cholesterol is a fat chemical (lipid) that is made in the cells in your body. Many different cells make cholesterol but cells in the liver make about a quarter of the total. Although many foods contain cholesterol, it is poorly absorbed by the gut into the body. Therefore, cholesterol that you eat in food has little effect on your body and blood cholesterol level. A certain amount of cholesterol is present in the bloodstream. You need some cholesterol to keep healthy. Cholesterol is carried in the blood as part of particles called lipoproteins. There are different types of lipoproteins, but the most relevant to cholesterol are:
- Low-density lipoproteins carrying cholesterol – LDL cholesterol. This is often referred to as bad cholesterol. This is the one mainly involved in forming atheroma. Atheroma is the main underlying cause of various cardiovascular diseases (see below). The majority of cholesterol in the blood is LDL cholesterol, but how much varies from person to person.
- High-density lipoproteins carrying cholesterol – HDL cholesterol. This is often referred to as good cholesterol. This may prevent atheroma forming.
What are atheroma and cardiovascular diseases?
Patches of atheroma are like small fatty lumps that develop within the inside lining of blood vessels (arteries). Atheroma is also known as atherosclerosis and hardening of the arteries. Patches of atheroma are often called plaques of atheroma.
Over months or years, patches of atheroma can become larger and thicker. So in time, a patch of atheroma can make an artery narrower. This can reduce the blood flow through the artery. For example, narrowing of the heart (coronary) arteries with atheroma is the cause of angina.
Sometimes, a blood clot (thrombosis) forms over a patch of atheroma and completely blocks the blood flow. Depending on the artery affected, this can cause a heart attack, a stroke, or other serious problems.
Cardiovascular diseases are diseases of the heart (cardiac muscle) or blood vessels (vasculature). However, in practice, when doctors use the term cardiovascular disease they usually mean diseases of the heart or blood vessels that are caused by atheroma.
What factors affect the blood level of cholesterol?
To an extent your blood cholesterol level can vary depending on your diet. However, different people who eat the same diet can have different blood cholesterol levels. In general, however, if you eat less fatty food in your diet your cholesterol level is likely to go down.
In some people a high cholesterol level is due to another condition. For example, an underactive thyroid gland, obesity, drinking a lot of alcohol and some rare kidney and liver disorders can raise the cholesterol level.
In some people a very high level of cholesterol runs in the family, due to a genetic problem with the way cholesterol is made by the cells in your body. One example is called familial hypercholesterolaemia.
Everybody has some risk of developing atheroma which then may cause one or more cardiovascular diseases. However, some situations increase the risk. These include:
- Lifestyle risk factors that can be prevented or changed:
- Treatable or partly treatable risk factors:
- High blood pressure (hypertension).
- High cholesterol blood level.
- High triglyceride (another type of fat) blood level.
- Kidney diseases that affect kidney function
Cholesterol blood levels
The following levels are generally regarded as desirable:
- Total cholesterol (TChol) – 5.0 mmol/L or less. However, about 2 in 3 adults in the UK have a TChol level of 5.0 mmol/L or above.
- LDL cholesterol after an overnight fast: 3.0 mmol/L or less.
- HDL cholesterol: 1.2 mmol/L or more.
- TChol/HDL ratio: 4.5 or less. That is, your TChol divided by your HDL cholesterol. This reflects the fact that for any given TChol level, the more HDL, the better
Who should be treated to reduce their cardiovascular health risk?
Treatment to reduce the risk of developing a cardiovascular disease is usually offered to people with a moderate or high risk. That is:
- People with a risk assessment score of 10-20% or more. That is, if you have a 1 or 2 in 10 chance or more of developing a cardiovascular disease within the next 10 years.
- People with an existing cardiovascular disease (to lower the chance of it getting worse, or of developing a further disease).
- People with diabetes. If you have diabetes, the time that treatment is started to reduce cardiovascular risk depends on factors such as:
- Your age.
- How long you have had diabetes.
- Your blood pressure.
- If you have any complications of diabetes.
- People with certain kidney disorders.