What is high cholesterol ?

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.