Cholesterol is a fatty substance known as a lipid. It's vital for the normal functioning of the body. Cell membranes, hormones and vitamin D are created by your body using cholesterol.
There are 2 main sources of the cholesterol in your blood:
- cholesterol in the food you eat
- cholesterol produced by your liver
Having an excessively high level of lipids in your blood (hyperlipidemia) can have an effect on your health.
High cholesterol, on its own, doesn't usually cause any symptoms but increases your risk of serious health conditions.
Cholesterol is carried in your blood by proteins. When the two combine, they're called lipoproteins. There are two main types of lipoprotein.
High-density lipoprotein (HDL) carries cholesterol away from the cells and back to the liver. From there it's either broken down or passed out of the body as a waste product. For this reason, HDL is referred to as "good cholesterol" and higher levels are better.
Low-density lipoprotein (LDL) carries cholesterol to the cells that need it. If there's too much cholesterol for the cells to use it can build up in the artery walls, leading to disease of the arteries. For this reason, LDL is known as "bad cholesterol".
The amount of cholesterol in the blood, both HDL and LDL , is measured with a blood test.
The recommended cholesterol levels in the blood vary between those with a higher or lower risk of developing arterial disease.
Why should I lower my cholesterol?
Evidence strongly indicates that high cholesterol can increase the risk of:
- narrowing of the arteries (atherosclerosis)
- heart attack
- transient ischaemic attack (TIA) – often known as a "mini stroke"
- peripheral arterial disease (PAD)
This is because cholesterol can build up in the artery wall, restricting the blood flow to your heart, brain and the rest of your body. It also increases the risk of a blood clot developing somewhere in your body.
Your risk of developing coronary heart disease also rises as your blood's cholesterol level increases. This can cause pain in your chest or arm during stress or physical activity (angina).
What causes high cholesterol?
Many factors can increase your chances of having heart problems or a stroke if you have high cholesterol.
- an unhealthy diet – in particular, eating high levels of saturated fat
- smoking – a chemical called acrolin, found in cigarettes, stops HDL transporting cholesterol from fatty deposits to the liver, leading to narrowing of the arteries (atherosclerosis)
- having diabetes or high blood pressure (hypertension)
- having a family history of stroke or heart disease
There's also an inherited condition called familial hypercholesterolaemia. This can cause high cholesterol even in someone who eats healthily.
Read more about the causes of high cholesterol
When should my cholesterol levels be tested?
Your GP may recommend that you have your blood cholesterol levels tested if you:
- have been diagnosed with coronary heart disease, stroke or mini stroke (TIA), or peripheral arterial disease (PAD)
- have a family history of early cardiovascular disease
- have a close family member who has a cholesterol-related condition
- are overweight
- have high blood pressure, diabetes or a health condition that can increase cholesterol levels
Read more about how cholesterol is tested
What should my cholesterol levels be?
Blood cholesterol is measured in units called millimoles per litre of blood, often shortened to mmol/L.
As a general guide, total cholesterol levels should be:
- 5mmol/L or less for healthy adults
- 4mmol/L or less for those at high risk
As a general guide, LDL levels should be:
- 3mmol/L or less for healthy adults
- 2mmol/L or less for those at high risk
An ideal level of HDL is above 1mmol/L. A lower level of HDL can increase your risk of heart disease.
Your ratio of total cholesterol to HDL may also be calculated. This is your total cholesterol level divided by your HDL level. Generally, this ratio should be below four, as a higher ratio increases your risk of heart disease.
Cholesterol is only one risk factor. The level at which specific treatment is required will depend on whether other risk factors, such as smoking and high blood pressure, are also present.
How can I lower my cholesterol level?
The first step in reducing your cholesterol is to maintain a healthy, balanced diet. It's important to keep your diet low in fatty food.
You can swap food containing saturated fat for fruit, vegetables and wholegrain cereals. This will also help prevent high cholesterol from returning.
Other lifestyle changes, such as taking regular exercise and giving up smoking, can also make a big difference in helping to lower your cholesterol.
If these measures don't reduce your cholesterol and you continue to have a high risk of developing heart disease, your GP may prescribe a cholesterol-lowering medication, such as statins.
Your GP will take into account the risk of any side effects from statins. The benefit of lowering your cholesterol must outweigh any risks.
Read more about how high cholesterol is treated