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.
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).
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 and perhaps by modest amounts of alcohol.
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.
The levels of total cholesterol fall into the following categories:
- ideal level: cholesterol level in the blood less than 5 mmol/l
- too high cholesterol level: between 5 and 6.4 mmol/
- very high cholesterol level: between 6.5 and 7.8 mmol/l
- extremely high cholesterol level: above 7.8 mmol/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. These other factors when present increase the sensitivity of the body to harm through cholesterol.
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 4 mmol/l or their LDL below 2 mmol/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.
We know that diet is a 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 particularly when poorly controlled
- alcohol abuse
- being overweight – this is probably the commonest cause of high cholesterol levels.
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). Repeated strokes can lead to loss of use of the limbs, and unfortunately is also a common cause of dementia.
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: research shows that 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. Of course, smokers also have a greatly increased risk of cancer in many different sites, such as lung, breast and womb etc.
- Diet: food is another important factor. A Mediterranean diet made up of bread, fruits, vegetables and small amounts of lean meat, fish (especially oily 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
- total cholesterol in the blood
- triglyceride (a form of fat)
- glucose (sugar, to see if you have diabetes)
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.
How is high cholesterol treated?
Cholesterol-lowering medicine is needed in two situations:
- Firstly, if you do not have cardiovascular disease but your risk of developing cardiovascular disease is high. Risk is established from standard cardiovascular risk prediction charts, which use key numbers such as blood pressure, weight and medical history. Usually, you will need cholesterol-lowering medicines if your 10 year risk of developing cardiovascular disease is more than 15 per cent. Lifestyle changes are often also needed.
- Or, secondly, if you have established cardiovascular disease; virtually all people with cardiovascular disease will need cholesterol lowering drugs
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.
They are extremely effective drugs, and generally very safe, with a very low chance of side-effects.
Although statins are normally very effective, non-statin treatments such as Eezetimibe 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.