Cholesterol is transported around your body attached to a protein in your blood. This combination of fat and protein is called a lipoprotein. There are different types of lipoprotein, depending on how much fat there is in relation to protein.
A small amount of your body’s cholesterol is transported as high-density lipoprotein (HDL), which is mostly protein and not much fat. HDL transports excess cholesterol from your tissues (including the walls of arteries) to your liver for disposal. As HDL helps prevent cholesterol building up in your blood vessels, you have a reduced risk of heart disease if you have high levels of this type. This is why HDL is often referred to as ‘good’ cholesterol.
Most of your body's cholesterol is transported as low-density lipoprotein (LDL). It consists mainly of fat, with not much protein. LDL transports cholesterol from your liver to your cells. High levels of LDL increase your risk of cardiovascular disease because LDL causes cholesterol to build up in your blood vessels. LDL is often called ‘bad’ cholesterol.
Triglycerides are another type of lipid that mostly come from fats in your food. Energy from your food that isn’t used immediately is converted into triglycerides and transported to fat cells for storage. This provides you with an important source of stored energy. Although most triglycerides are stored as fat, low levels are also found in your blood. Having a raised level of blood triglycerides together with high LDL can increase your risk of heart disease, particularly if you have diabetes, high blood pressure or you smoke.
If you have a high total cholesterol level, this is a risk factor for future health problems, such as cardiovascular disease. But the ratio of how much HDL you have compared to total cholesterol is important too. This is called your total cholesterol (TC) to HDL cholesterol ratio (TC:HDL). You should aim for a high level of HDL cholesterol and a low level of LDL (a low TC to HDL ratio).
You may only find out that you have high cholesterol if you have a cholesterol test as part of a health check up, or if you develop symptoms of heart disease. Sometimes, yellow patches (called xanthomas) may develop around your eyes or elsewhere on your skin – these are cholesterol deposits and may show that you have high cholesterol.
Your cholesterol level is measured with a blood test. Usually you will be asked not to eat for 12 hours before the test so that your food is completely digested and doesn't affect the result. Your doctor or nurse may take a blood sample using either a needle and syringe, or a finger prick. You can have your cholesterol tested at your doctor’s surgery, at hospital, or as part of a health assessment examination.
Home-testing kits for cholesterol are also available but may not be very accurate. Speak to your pharmacist about your result if you use a kit.
The amount of cholesterol in your blood is measured in units called millimoles per litre of blood, usually shortened to 'mmol/litre', 'mmol/L' or 'mM'. When looking at your cholesterol levels, your doctor will consider how much HDL you have compared to total cholesterol. This is called your total cholesterol to HDL cholesterol ratio. You can work this out by dividing your total cholesterol level by your HDL level. It’s healthiest to have high HDL, low LDL and low total cholesterol, with total cholesterol to HDL ratio of less than four.
There is no recommended target level of cholesterol, unless you already have cardiovascular disease or are at high risk. In these instances, your cholesterol levels should ideally be:
- under 4mmol/l for total cholesterol
- under 2mmol/l for LDL cholesterol
- above 1mmol/l for HDL cholesterol
- under 1.7mmol/l for triglycerides
The levels of cholesterol in your blood can vary from day to day, so your doctor may take a series of different readings before recommending any treatment.
Who should have a cholesterol test?
If you’re at high risk of cardiovascular disease or you have a family history of high cholesterol, you should have your cholesterol levels checked. Speak to your doctor about how often it should be tested. Your doctor should check your cholesterol levels every year if you have cardiovascular disease.
If you have high cholesterol, there are two ways in which you can reduce it. The first is with lifestyle changes, which include changing your diet, managing your weight and exercising. The second is to combine lifestyle changes with cholesterol-lowering medicines.
By eating healthily, you can reduce your cholesterol levels. Your diet should be low in saturated fats in particular, and low in fat overall. Biscuits, cakes, pastries, red meat, hard cheese and butter all tend to be high in saturated fats, so it’s good to cut down on these foods.
Some foods such as eggs, prawns and offal (for example, liver and kidneys) contain cholesterol. This type of cholesterol is known as dietary cholesterol and it has a much lower effect on blood cholesterol than saturated fat in your diet. You may need to cut down on these foods if your doctor advises you to.
It's also important to include plenty of fibre in your diet, especially soluble fibre, which helps to lower cholesterol. There is soluble fibre in fruits and vegetables, beans and oats. Aim to eat at least five portions of fruit and vegetables each day. Eating foods containing substances called plant sterols or stanols, contained in some yoghurts or spreads, may help to lower high cholesterol, but they are not a substitute for a healthy diet.
If you're overweight, losing your excess weight can reduce your LDL levels and increase your HDL levels. Increasing your physical activity may enhance the cholesterol-lowering effects of your diet.
As high cholesterol can increase your risk of heart disease, you should reduce any additional risk of developing it, such as by stopping smoking.
Medicines are generally recommended either if you already have cardiovascular disease or if your risk of getting it is more than 20 percent over 10 years. Your risk can be calculated by your doctor, using a computerised calculation that takes into account a number of other risk factors. The aim of treatment for people with cardiovascular disease is to reduce total cholesterol levels by a quarter or to less than 4mmol/L.
The main group of medicines for lowering cholesterol are called statins. Statins available in the UK include simvastatin, atorvastatin, fluvastatin, pravastatin, and rosuvastatin. These medicines work by reducing the production of cholesterol in your liver, but can have side-effects such as indigestion and muscle pains.
Other types of medicines used to reduce cholesterol include fibrates, nicotinic acid and cholesterol-absorption inhibitors such as ezetimibe (Ezetrol), but these are generally less effective than statins or have more side-effects. If you have very high cholesterol, your GP may prescribe ezetimibe with statins. Your doctor can tell you more about these medicines and suggest the most suitable treatment for you.
There are several factors that may contribute to you having high cholesterol. These include:
- having a diet high in saturated fat
- a lack of exercise
- being obese (having a body mass index (BMI) of 30 or more)
- drinking more than the recommended daily amount of alcohol (this increases the level of triglycerides in your blood)
- age and gender – your cholesterol levels generally rise with increasing age and can be affected by your gender
If you're a man younger than 55 you're more likely to have high cholesterol than a woman. If you’re a woman over 55 and past the menopause, your cholesterol levels are likely to increase.
High cholesterol can sometimes be caused by a condition that runs in your family called familial hypercholesterolaemia (FH). In the UK, about one in 500 people have this condition. It’s not caused by an unhealthy lifestyle but is passed through families by a faulty gene.
Other conditions, such as poorly controlled diabetes, certain kidney and liver diseases and underactive thyroid (hypothyroidism) may also cause your levels of cholesterol or triglycerides to be high. Some medicines such as the oral contraceptive pill, beta-blockers, steroids or thiazides (a type of diuretic) may also affect your blood lipid levels.
If you have high cholesterol, it increases your risk of heart disease and stroke. It may also affect arteries elsewhere in your body such as your legs – this is known as peripheral arterial disease.
You may be able to prevent high cholesterol by keeping to a healthy weight and eating a diet that is low in saturated fat. Try to include at least two portions of fish per week in your diet, of which at least one should be an oily fish such as mackerel or salmon. Try to take regular exercise, avoid smoking and stick to recommended limits of alcohol.
If you don’t have high cholesterol, consuming products containing plant sterols or stanols, such as yogurts or spreads, is not recommended (and they are not suitable for women who are pregnant or breastfeeding).
Are all statins the same?
Statins available in the UK vary slightly in their cholesterol-lowering effects. Your doctor will prescribe you a statin at a dose that he or she thinks is suitable for reducing your cholesterol levels, with as few side-effects as possible.
There are different types of statin available in the UK. Examples include simvastatin, atorvastatin, and fluvastatin. All statins work in the same way, but may have different chemical structures. Statins lower the level of cholesterol in your blood, especially LDL or 'bad' cholesterol. Having a low cholesterol level reduces your risk of heart disease, including heart attacks.
The dose you take affects how much cholesterol the statin removes from your blood. Different statins may be prescribed at different doses to remove the same amount of cholesterol. These doses may also have different effects on your cholesterol levels over different periods of time. Your cholesterol levels will be checked regularly and the dose of your statin may be modified by your doctor.
As with any medicine, you may have some side-effects when taking statins, but these are generally mild and similar for all types of statin. Your doctor will monitor possible side-effects by doing a liver function blood test before you start taking the statin and again a few months later. If your liver function is affected, you may need to take a different statin.
How do the fats in my food affect my cholesterol levels?
Fat is a good source of energy but eating too much of the wrong types of fat increases your cholesterol levels and therefore your risk of heart disease.
Some fat is an essential part of a healthy diet, but it's important you don't eat too much of it and that you're careful about the type of fat that you eat.
Your liver turns the fat in your blood into cholesterol. Your blood then transports the cholesterol around your body. Not all cholesterol is bad for you; there is a harmful form and a protective form. The harmful form of cholesterol is called LDL or low-density lipoprotein. The protective form is called HDL or high-density lipoprotein.
You can help lower your cholesterol level by reducing the amount and type of fat that you eat. There are different types of fat in food.
- Saturated fats – these increase your cholesterol levels. Examples of foods high in saturated fat include cakes and biscuits, pastry, meat products and hard cheese.
- Trans fats – these have a similar effect on your cholesterol levels as saturated fats. Foods containing hydrogenated vegetable oil (which must be listed in the ingredients list on the label) might contain trans fats. Trans fats currently don't need to be labelled separately on food labels. They can be found in biscuits and cakes, fast food and some margarines.
- Monounsaturated fats – these help lower harmful cholesterol levels. Examples of foods high in monounsaturated fats include olive oil and rapeseed oil.
- Polyunsaturated fats – these lower both harmful and protective cholesterol levels. Examples of foods high in polyunsaturated fats include sunflower oil and soya oil.
When you're shopping for food, compare the labels so you can pick those with less total fat or less saturated fat. Buy lower fat versions of dairy foods, such as semi-skimmed or skimmed milk, and reduced-fat yoghurt, whenever you can.
There is a particular type of polyunsaturated fat called omega-3 which can help to reduce your cholesterol levels. The best source of omega-3 fats is oily fish, such as kippers, mackerel, sardines and salmon. You should aim to eat two portions of fish per week, of which one should be oily, but not more than two portions per week if you're pregnant or breastfeeding.
If you're worried about high cholesterol, ask your doctor for advice.
What is the normal level of cholesterol that I should have in my blood?
Too much cholesterol in your blood can increase your risk of heart problems. There is no recommended target cholesterol level unless you have cardiovascular disease or are at high risk of getting it. For example, if you already have heart disease, your doctor may advise you to aim for a total cholesterol level under 4mmol/L. Generally, the lower your cholesterol the better.
Cholesterol is a fatty substance that plays an essential role in how every cell in your body works. Your body makes most of your cholesterol and your blood transports it attached to a protein. This combination of fat and protein is called a lipoprotein and there are several types. LDL is often called 'bad' cholesterol because it causes cholesterol to build up in your blood vessels and HDL 'good' cholesterol because it helps prevent cholesterol building up.
There is no recommendation for the ideal level of total cholesterol or LDL. Your doctor will consider your cholesterol levels as part of your overall cardiovascular risk, taking into account other risk factors such as your age, sex, body mass index (BMI), blood pressure, family history and whether you smoke, drink alcohol or have any other illness such as diabetes.
When looking at your cholesterol levels, your doctor will consider how much HDL you have compared to your total cholesterol level. This is called your total cholesterol to HDL cholesterol ratio. You can work this out by dividing your total cholesterol level by your HDL level. It's healthiest to have high HDL, low LDL and low total cholesterol, with a total to HDL ratio of less than four.
If you have cardiovascular disease, have had a heart attack, get angina or have had an ischaemic stroke, your doctor will be aiming to help you reduce your total cholesterol level to less than 4mmol/L, and your LDL to less than 2mmol/L. He or she will be able to prescribe statins and give you advice about diet and exercise to help meet this target.
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- Joint Formulary Committee, British National Formulary. 64th ed. London: British Medical Association and Royal Pharmaceutical Society of Great Britain; 2012
- Lipid modification. Prodigy. www.prodigy.clarity.co.uk, accessed 16 November 2012
- Lipid modification: cardiovascular risk assessment and the modification of blood lipids for the primary and secondary prevention of cardiovascular disease. National Institute for Health and Clinical Excellence (NICE), May 2008. www.nice.org.uk
- Statins. British Heart Foundation. www.bhf.org.uk, published 1 April 2012
- Cholesterol and health. Heart UK. www.heartuk.org.uk, accessed 16 November 2012
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- Atherosclerosis. The Merck Manuals. www.merckmanuals.com, published January 2008
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