Why should you have your cholesterol levels tested?

A cholesterol level gauge showing normal levels

BHF Associate Medical Director Mike Knapton tells Senior Cardiac Nurse Emily Reeve what causes high cholesterol, how it affects your heart, and what you can do about it.

What is cholesterol?

Cholesterol is a kind of fatty substance found in the blood. It is made by the liver and we all have some of it circulating naturally in our bodies. The body needs it to work – it is used by every cell, helps make vitamin D and some hormones, and is a component of bile.

The higher your cholesterol, the higher your risk of going on to have a heart attack or stroke. But you can’t tell how high it is without a test, which is why it’s important to get tested.

Why does high cholesterol increase your risk of heart attack and stroke?

Too much cholesterol in your blood can cause fatty material to build up in your artery walls. This can lead to a heart attack or stroke. This can happen if a piece of the fatty material breaks off, causing a blood clot to form, which might block an artery. If this happens in an artery supplying your heart, this is a heart attack, or if it’s an artery supplying your brain, this is a stroke.

What should I find out when I get tested?

You’ll have a simple blood test as part of an NHS Health Check (in England, if you aren’t already diagnosed with a long-term condition). If you have coronary heart disease, your blood cholesterol should already be monitored by your doctor. When you get tested, ask your doctor to tell you the levels of your: total cholesterol, HDL cholesterol, LDL cholesterol, non-HDL cholesterol, and triglycerides.

But what do all these terms mean?

Cholesterol levels vary, but generally the lower the LDL and higher the HDL, the better

There are two main types of cholesterol – LDL or ‘bad’ cholesterol and HDL or ‘good’ cholesterol. LDL carries cholesterol from your liver to the cells that need it. But if you have too much in your blood, it can cause fatty material to build up in your artery walls, which raises your risk of heart attack and stroke. HDL carries cholesterol away from the cells back to the liver to get broken down, which is why it’s a ‘good’ type of cholesterol.

HDL stands for high-density lipoprotein and LDL stands for low-density lipoprotein. Lipoproteins are packages made up of fats (particularly cholesterol) and proteins. Cholesterol, like other fats, doesn’t dissolve easily in water, so it travels through the blood with protein. There are other types of ‘bad’ cholesterol too, which is why we talk about non-HDL cholesterol. The level of this is your total cholesterol minus HDL cholesterol level. This is important as it is a measure of all the ‘bad’ cholesterol.

Triglycerides are another kind of fat – a blood lipid test looks at all the fats in your bloodstream, not just cholesterol. Triglycerides are also made naturally in the body by your liver, and a high level also raises your risk of heart and circulatory disease. They are found in foods like meats, dairy produce and cooking oils.

What are normal cholesterol levels?

Cholesterol levels vary from person to person, but in general the lower the LDL and non-HDL, the better, and higher the HDL, the better. Your blood cholesterol is measured in mmol/L, which stands for millimoles per litre.

You should aim to have:

  • total cholesterol 4mmol/L or less for those at high risk
  • non HDL-cholesterol of 3mmol/L or less for those at high risk
  • LDL-cholesterol of 2mmol/L or less for those at high risk

When should I be worried?

There’s no level of cholesterol at which we can say you will or won’t have a heart attack. Most doctors don’t base advice or treatment on cholesterol results alone unless you have familial hypercholesterolemia. That’s why the numbers above only refer to those at high risk. If you’re not at high risk, your doctor looks at cholesterol alongside other risk factors (usually part of a NHS Health Check), such as blood pressure and body mass index (your weight/height ratio), and lifestyle factors such as smoking, diet and physical activity.

What cholesterol level means I need medication?

'Cholesterol levels vary, but generally the lower the LDL and higher the HDL, the better

A decision about medication is based on all your risk factors, not just cholesterol. A cardiovascular risk assessment predicts your risk of heart attack or stroke in the next 10 years. The computer programme that predicts it is called QRISK, so you may hear your doctor talk about a ‘QRISK score’. If it suggests a 10 per cent risk or higher, you may be offered dietary advice and drug treatment (usually a statin) to help lower your cholesterol. The treatment is usually long-term. Increasingly, we are looking at an individual’s lifetime risk, rather than just a 10-year risk, and basing the advice on that figure. You can get an idea of your lifetime risk, or ‘heart age’, by using the online Heart Age Tool, which was developed by the BHF with Public Health England.

If you already know your cholesterol levels, that will make the tool more accurate. If you have already developed heart disease, then taking statins has been proven to reduce your risk of a heart event, even if your cholesterol levels aren’t high.

Can I control my cholesterol through diet, without taking medication?

Eating lots of fruit and vegetables, whole grains (especially oats), and beans and lentils can help lower your cholesterol. You can also help by losing weight, avoiding foods that are high in saturated fat, quitting smoking and being active. It’s important to understand that though lifestyle measures can help, in some circumstances you may still be recommended to take medication as well. If you’re concerned about taking medication, discuss this with your doctor.

What’s changed when it comes to cholesterol?

We now have some very good studies from the 1990s and onwards, which show that those who have had a heart attack will reduce their risk of having another one by taking a statin. People who haven’t had a heart attack, but are at high risk of one, can also reduce their risk by taking a statin. Because we know more about the different types of ‘bad’ cholesterol, you’re now much more likely to be told about non-HDL cholesterol, rather than just LDL and HDL cholesterol. And these days, cholesterol tests don’t usually require you to fast beforehand.

We now know more about the inherited nature of high cholesterol in some people – in particular, an inherited condition called familial hypercholesterolaemia (FH), which causes very high cholesterol levels, and if left untreated can cause heart attacks at a young age. The BHF has funded a great deal of this research, as well as helping to implement nationwide screening, which means that people with FH can be identified at a young age and offered treatment to reduce their heart attack risk.


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