Cholesterol facts
| Diet is just one of the things that can reduce cholesterol. |
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:
Each group has a different function in the body.
high-density lipoproteins (HDL)
low-density lipoproteins (LDL)
very low-density lipoproteins (VLDL)
chylomicrons.
How do they affect cardiovascular health?
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.
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:
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.
LDL cholesterol
People with diabetes who have an LDL cholesterol level of more than 2mmol/l should generally receive cholesterol-lowering drug treatment.
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.
When the HDL is greater than 1, this has the effect of lowering the TC/HDL ratio, lowering your risk.
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).
Some people find they are intolerant of statins and experience side-effects, such as muscle pains, fatigue and nausea. If that occurs, there are a number of prescribable alternatives - such as ezetimibe or fibrate drugs, which may not cause these problems.
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