High cholesterol level (hypercholesterolaemia)
Reviewed by Dr Neal Uren, consultant cardiologist and Dr Stephen CP Collins, GP 103
What is cholesterol?
Cholesterol is one of the body's fats (lipids). Cholesterol and another lipid, triglyceride, are important building blocks in the structure of cells and are also used in making hormones and producing energy.To some extent, the cholesterol level in blood depends on what you eat, but it is mainly dependent on how the body makes cholesterol in the liver.
Having too much cholesterol in the blood is not a disease in itself, but can lead to the hardening and narrowing of the arteries (atherosclerosis) in the major vascular systems.
For the sake of simplicity, there are two sorts of cholesterol: a 'good' sort called high-density lipoprotein (HDL) and a 'bad' sort called low-density lipoprotein (LDL).
HDL has a useful effect in reducing cholesterol and taking it back to the liver. HDL actually protects against atherosclerosis.
LDL can contribute to diseases of the heart and circulation (cardiovascular disease).
It is the proportion of LDL cholesterol to HDL cholesterol that influences the degree to which atherosclerosis is likely to cause problems (cardiovascular risk).
LDL cholesterol level can be lowered by eating a low fat diet and, if necessary, taking medication. HDL cholesterol level can be raised by exercising.
What is high cholesterol?
Did you know?
Cholesterol levels rise slightly with age.
Women generally have a higher HDL cholesterol level than men.
A blood sample, taken after a person has fasted for several hours, can be used to measure the levels of all forms of cholesterol.
In the UK, the average total cholesterol level is 5.7mmol/l.
The levels of total cholesterol fall into the following categories:
ideal level: cholesterol level in the blood less than 5mmol/l.
mildly high cholesterol level: between 5 to 6.4mmol/l.
moderately high cholesterol level: between 6.5 to 7.8mmol/l.
very high cholesterol level: above 7.8mmol/l.
As well as this figure, doctors also have to take into account:
the ratio between good and bad cholesterol
the presence of other risk factors for cardiovascular disease, such as smoking, diabetes and high blood pressure.
It is possible for someone to have a high level of total cholesterol and still have a relatively low cardiovascular risk because of an absence of other risk factors or because their family history is free from coronary disease.
Anyone with an established track record of cardiovascular disease such as angina (chest pain), a previous heart attack, coronary angioplasty or coronary bypass surgery should seek advice to keep their total cholesterol level below 5mmol/l or their LDL below 3mmol/l.
What can cause high cholesterol levels?
Both hereditary and environmental factors affect the cholesterol level.
Cholesterol levels can run in families. If the inherited cholesterol levels are very high, this is called familial hypercholesterolaemia (FH). Familial combined hyperlipidaemia (FCH) is where the triglyceride levels are very high as well.
Levels can also be influenced by the part of the world you live in: cholesterol levels in northern European countries are higher than in southern Europe and much higher than in Asia.
We know that diet is a major factor, with diets that are high in saturated fat (cakes, pastry, meat, dairy products) raising cholesterol.
High cholesterol is also seen in connection with other diseases such as:
reduced metabolism due to thyroid problems
kidney diseases
diabetes
alcohol abuse.
What are the symptoms of high cholesterol in the bloodstream?
You can't feel whether you have high cholesterol levels in the same way that you can a headache, but a high level combined with other risk factors can lead to atherosclerosis and symptoms of cardiovascular disease.
Atherosclerosis is the build up of cholesterol and fat (fatty deposits or plaques) in the artery walls. The arteries become narrow and hardened, their elasticity disappears and it becomes difficult for blood to flow through.
These fatty plaques can rupture, causing blood to clot around the rupture. If blood can't then flow to a part of the body, the tissue dies.
The following are all symptoms of cardiovascular disease. They depend on the degree of narrowing, the likelihood that the plaque is going to rupture (vulnerability), and the organ supplied by the affected arteries.
If the arteries that supply the lower limbs narrow, this can cause leg pain when walking or running (intermittent claudication). If a clot suddenly blocks the major peripheral vessel to the lower limb, it may starve the leg of blood to such an extent that it requires amputation.
In the brain, a blood clot (thrombus) may block an artery or a smaller blood vessel may rupture, causing local haemorrhage (bleeding). Either will result in a stroke.
In the heart, narrowed coronary arteries cause angina and ruptured plaques cause blood clots that can lead to a heart attack. This may lead to reduced heart function if a significant amount of heart muscle is damaged.
If the carotid arteries in the neck become narrow, clots may form and float to the brain. This can result in a stroke or repeated 'mini-strokes' (transient ischaemic attacks or TIAs).
It's common for those most affected by atherosclerosis to have the disease in several arteries, including:
the aorta, the main artery in the chest and abdomen
renal (kidney) arteries
mesenteric (intestinal) vessels.
What can be done to prevent cardiovascular disease?
High cholesterol is only one of many risk factors that lead to hardening of the arteries. Other major risk factors are listed below.
Smoking: recent research shows that middle-aged women and men who smoke have a much higher risk of suffering a heart attack. The risk drops in the years following giving up smoking.
Diet: food is another important factor. A Mediterranean diet made up of bread, fruits, vegetables and small amounts of lean meat, fish, and olive oil is recommended.
Alcohol: moderate consumption reduces the negative effect of the LDL cholesterol and increases HDL cholesterol. Too much raises blood pressure and damages the liver, having an adverse overall effect.
Exercise: even on a small scale this can reduce the chance of coronary artery disease. Hard physical exercise increases the blood's ability to break up blood clots.
Body weight: it is important to avoid obesity, especially when fat is around the stomach.
How does the doctor make the diagnosis?
After a 12-hour fast in which only water is consumed, a blood sample is taken to determine the level of:
LDL cholesterol
HDL cholesterol
triglyceride
total cholesterol in the blood.
Test levels are adjusted to take into account age, weight, diabetes, kidney diseases and decreased metabolism.
Cholesterol count also rises during pregnancy and drops significantly for at least three months after a heart attack.
The doctor can make a rough estimate of the extent of cardiovascular disease by checking the pulse, the blood pressure, listening to the heart and large arteries, checking kidney function with a blood test and arranging an exercise stress test.
How is high cholesterol treated?
Cholesterol-lowering medicine is needed if your total cholesterol level remains higher than 5mmol/l and you already have cardiovascular disease.
Medication may also be needed when changes to diet and lifestyle fail to reduce your risk of cardiovascular disease.
Did you know?
There are now national guidelines to help your doctor estimate the cardiovascular risk for your cholesterol and blood pressure readings.
Your doctor can calculate your 'cardiovascular risk' based on key numbers such as blood pressure, weight and medical history.
UK guidelines are that medication should be started when an individual's risk of coronary disease is greater than 30 per cent over 10 years.
Statins (eg simvastatin, atorvastatin, rosuvastatin) are the most effective medicines for lowering cholesterol. These reduce the production of 'bad' LDL cholesterol by the liver, which decreases LDL cholesterol blood levels by up to 50 per cent.
Although statins are normally very effective, non-statin treatments such as Ezetrol (ezetimibe) are available if there are any problems with side-effects such as muscle pains. These can also be used in conjunction with statins if cholesterol levels remain high, or if a high level of statin causes side effects. Older treatments also exist such as fibrates which can be very effective when used in conjunction with more modern treatments.
Based on a text by Dr Annebirthe Bo Hansen, specialist
