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| High cholesterol level (hypercholesterolaemia) |
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Reviewed by Dr Neal Uren, consultant cardiologist and Dr Stephen CP Collins, GP
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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).
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HDL has a useful effect in reducing cholesterol and taking it
back to the liver. HDL actually protects against atherosclerosis.
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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?
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Did you know?
Cholesterol levels rise slightly with age.
Women generally have a higher HDL cholesterol level than
men.
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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:
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ideal level: cholesterol level in the blood
less than 5mmol/l.
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mildly high cholesterol level: between 5 to
6.4mmol/l.
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moderately high cholesterol level: between
6.5 to 7.8mmol/l.
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very high cholesterol level: above 7.8mmol/l.
As well as this figure, doctors also have to take into
account:
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the ratio between good and bad cholesterol
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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:
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.
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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.
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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.
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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.
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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:
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the aorta, the main artery in the chest and abdomen
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renal (kidney) arteries
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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.
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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.
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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.
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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.
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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.
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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:
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LDL cholesterol
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HDL cholesterol
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triglyceride
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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.
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Did you know?
There are now national guidelines to help your doctor estimate
the cardiovascular risk for your cholesterol and blood pressure readings.
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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.
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Based on a text by Dr Annebirthe Bo Hansen, specialist
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Last updated 04.07.2008
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