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Reviewed by Professor Ian Campbell, consultant physician
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| Diet is just one of the things that can reduce
cholesterol. |
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A high level of cholesterol is one of the factors that can
increase your risk of cardiovascular disease, eg
angina,
heart disease and
stroke.
This is because high levels of cholesterol lead to fatty
deposits that cause the arteries to narrow (atherosclerosis) and
restrict blood flow to the heart. This is what causes cardiovascular
disease.
What is cholesterol?
Cholesterol is an important substance that's used by the body
in many ways.
It's the starting point of manufacture for many of the body’s
natural steroid hormones and for vitamin D, which controls calcium in the
body.
It is also an essential component of the membrane that forms the
walls of individual cells in all tissues.
Eighty per cent of the cholesterol we have is produced within
our own body – mostly by the liver. It's then transported from the liver via
the blood stream to other tissues.
Cholesterol travels through the blood in minute packages mixed
with large molecules called lipoproteins. Lipoproteins are themselves
combinations of fats and proteins.
Fats such as cholesterol don't dissolve well in the blood
stream, but become soluble when coated with lipoproteins.
What are lipoproteins?
Four main groups of lipoproteins exist, based mainly on their
different sizes and density:
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high-density lipoproteins (HDL)
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low-density lipoproteins (LDL)
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very low-density lipoproteins (VLDL)
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chylomicrons.
Each group has a different function in the body.
How do they affect cardiovascular health?
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High-density lipoproteins (HDL) mop up excess
cholesterol in the body and return it to the liver for re-processing. HDL is
often called good cholesterol and raised levels give
protection against heart disease.
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Low-density lipoproteins (LDL) transport
cholesterol from the liver to be deposited elsewhere in the body. LDL is known
as bad cholesterol because it deposits cholesterol in the
lining of your arteries. The more LDL you have, the more likely you are to
develop heart disease.
What affects levels of lipoproteins?
Men generally have higher levels of LDL compared to
women.
This is probably because of the protective effect of oestrogen,
one of the female hormones. Following the
menopause, this
difference disappears.
Exercise raises HDL levels, as does modest alcohol intake.
Why test cholesterol?
Every adult should have it measured at least once before they
are far past middle age.
Cholesterol is easily measured in a blood sample. If high
cholesterol runs in your family, it's better to measure cholesterol at a much
younger age - some time in your 20s.
Cholesterol levels don't tend to fluctuate, so if you have a
normal level it doesn't need to be repeated for many years.
If it's high, it may need quite frequent re-testing to gauge the
effect of treatment.
What do the figures mean?
Total cholesterol
This is the single figure for your cholesterol level, which is
all the subtypes combined.
The desirable upper limit of total cholesterol (TC) for people
who have diabetes is 4mmol/l.
As with the other risk factors for cardiovascular disease,
raised cholesterol is of more concern if there are other factors
present:
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someone who has a TC of 6mmol/l, but is fit, is not
overweight, has no family history of heart disease and doesn't have
diabetes or
smoke will have little or no benefit
from lowering their cholesterol.
-
someone with the same cholesterol level but who smokes, is
overweight and has
high blood pressure
will reduce his cardiovascular risk quite a lot by getting his cholesterol
down.
HDL cholesterol
The usual range of HDL levels is 0.5 to
1.6mmol/l.
Higher levels are good. Cholesterol experts often divide the
total cholesterol (TC) by the HDL level to give a better judge of your risk
level than the TC alone.
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When the HDL is greater than 1, this has the effect of
lowering the TC/HDL ratio, lowering your risk.
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When the HDL is low, the TC/HDL ratio goes up and so does
your risk.
How can I lower my cholesterol levels?
Most cholesterol in the body is produced in the liver. This
means dieting only has a small effect on levels.
Even so, this amount is still helpful, especially as part of a
healthier diet in general. Some cholesterol-lowering margarines may also be
helpful.
A large proportion of the UK population will not achieve target
cholesterol levels without extra help in the form of cholesterol-lowering drug
treatment.
Cholesterol treatment and diabetes
The most common drug that is prescribed is a
statin. Statins
should be prescribed as primary prevention in all diabetic patients over 40
years old with a TC of more than 4mmol/l or and LDL-cholesterol of more than
2mmol/l.
Statins may be prescribed to younger diabetic patients if
there are additional risk factors for cardiovascular disease or there is
evidence of diabetic eye disease
(retinopathy) or diabetic kidney disease
(nephropathy).
All diabetic patients with a history of heart attack, stroke
or cardivascular disease should be prescribed a statin to preven further
attacks (secondary prevention).
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References
National Institute for Health and Clinical Excellence. The
management of Type 2 diabetes (update). www.nice.org.uk/CG66
Bhatnagar D, Soran H, Durrington PN. Hypercholesterolaemia and
it's management. BMJ 2008; 337: 503-8.
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Based on a text by Dr Dan Rutherford, GP
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Last updated 12.09.2008
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