High cholesterol can lead to heart disease and stroke, so make sure yours is within healthy levels

It is often derided as a health baddie but the fatty substance called cholesterol is actually essential for making cell membranes, hormones and bile salts. High levels are associated with a higher risk of coronary artery disease due to hardening of the arteries - a condition known as atherosclerosis - and it is believed that around 70 per cent of adults in the UK have a blood level of cholesterol high enough to be a health risk.

What is it?
Cholesterol belongs to a chemical family called lipids, which are found in cell membranes throughout the body. Lipids, including fat and triglycerides, are also used to produce hormones, vitamin D and the bile acids that aid the digestion of fat. But you don't need to worry about getting enough in your diet, as the body is able to meet its needs by producing cholesterol in the liver.

The good and the bad
Not all cholesterol is bad. It is transported around the body in three forms known as 'lipoproteins.'

• LDL or low-density lipoprotein. Often called 'bad' cholesterol, because too much can lead to cholesterol build-up and blockage in the arteries. LDL cholesterol carries most of the cholesterol in the blood.
• HDL or high-density lipoprotein, or 'good' cholesterol, helps transport cholesterol from other parts of the body to the liver. This helps remove it from the body, therefore preventing it from piling up in the arteries.
• A third type of lipoprotein, which is very low in density, transports triglycerides in the blood; high levels of triglycerides have also been linked to increased risk of heart disease.

Cholesterol and hardening of the arteries
The level of cholesterol in the blood increases as we eat more amounts of saturated fats. Most people with high cholesterol have a diet rich in whole-milk dairy products, eggs, animal fats or meat. If extra cholesterol and fat in the blood undergo a chemical reaction called oxidation, they are taken up by scavenger cells which, when over-laden, become trapped and are deposited in the inner walls of the arteries that supply blood to the heart. These deposits make the arteries narrower and narrower, contributing to atherosclerosis and, if unchecked, coronary heart disease.

Eating plenty of fruit and vegetables supplies substances called antioxidants which protect circulating cholesterol from oxidation, and lowers the risk of atherosclerosis.

What is coronary heart disease?
The single biggest killer in the UK is coronary heart disease. Like any muscle, the heart needs a constant supply of oxygen and nutrients, which are carried to it by blood in the coronary arteries. When these arteries become narrowed or clogged and cannot supply enough blood to the heart, the result is CHD.

Measuring cholesterol
Blood cholesterol levels are measured by means of a small blood sample with a syringe and needle, or from a finger prick. The initial test measures the total amount of cholesterol, good and bad. This level can vary from day to day, or even during the day, so a series of tests may be needed if your doctor has any worries that your results may be high. Further testing may be done to measure the exact amounts of the various different types of lipoprotein.

The units used to measure blood levels of cholesterol are mmol/l - or millimoles per litre.

What's a safe level?
Not all doctors agree on exactly what the normal or 'safe' level of cholesterol in the blood should be but most authorities agree that, in adults aged under 60, total cholesterol should be less than 5 mmol/l; LDL should be less than 3.0 mmol/l; and HDL should be more than 1 mmol/l for men, or 1.2 mmol/l for women.

If you are at high risk of developing CHD within the next 10 years, total cholesterol should be even lower below 4mmol/l, with LDL-cholesterol below 2 mmol/l. This usually means having to take a cholesterol-lowering drug called a statin.

An estimated 72% of men and 69% of women aged 35 to 64 years have raised total cholesterol levels above 5mmol/l in the UK, with an average of 5.8mmol/l. This means that many people in this country have a cholesterol level that carries health risks. The higher the level of cholesterol, the higher the risk of heart disease.

Those at risk
If you have heart disease or risk factors for heart disease, such as diabetes, a family history of the disease, or if you smoke, you should pay even more attention to cholesterol level. Your doctor may suggest treatment to lower your cholesterol to keep it within a healthy range.

Treatment
If your cholesterol was found to be high on routine testing, or you have already had problems related to arterial disease, your doctor will probably advise medication and lifestyle changes.

Lifestyle changes

• Lose weight, or avoid becoming overweight. Even 5-10 pounds will have a significant effect on your cholesterol.
• Take more exercise. Exercise helps increase the amount of HDL, the 'good' cholesterol, as well as helping with weight loss.
• Modify your diet. It's important to reduce the amount of saturated fats, usually fats from animal sources, while still having a well-balanced, nutritious and enjoyable diet. Changing your diet can achieve up to a 10 per cent fall in cholesterol levels.

Medication
In addition to lifestyle changes your doctor may prescribe drugs to lower your cholesterol. This will depend on risk factors such as age, smoking, high blood pressure, low levels of HDL cholesterol and a family history of heart disease, particularly in men younger than 55 or women younger than 65.

If you don't achieved your target LDL cholesterol level after three months on a single medication, your doctor may recommend adding a second one. Various combinations have been shown to be effective and safe. Lower doses of each individual drug can reduce the risk of side effects.

Types of drugs
Statins. Introduced in the mid 1990's, these drugs can lower cholesterol by up to 20 per cent by inhibiting an enzyme called HMG-CoA reductase, which controls the body's cholesterol production rate.

The two prescribed in the UK are simvastatin and pravastatin. A trial has shown statins to be effective in reducing the risks of heart attack and stroke in high-risk people by around one third.

Statins are taken once a day in the evening or before bed. The timing is important, since the body makes more cholesterol at night than during the day. It takes about four to six weeks to achieve the full effect.

A selective cholesterol absorption inhibitor, called ezetimibe, works by reducing the amount absorbed from the intestines. It is used in addition to a statin drugs and helps 72% of those unable to reach recommended cholesterol levels with a statin alone to reach their goal.

A bile acid sequestrant (colestryramine) and an anion-exchange resin can typically lower cholesterol by 10-20 per cent and are available as powders or tablets. They bind with bile acids that contain cholesterol in the intestines, and the cholesterol complexes are then eliminated in the stool. They may be prescribed in combination with another drug if you have high triglycerides or a history of severe constipation.

Fibrates. These drugs reduce triglycerides by 20-50 per cent and raise HDL cholesterol 10-15 per cent. Fibrates drugs include bezafibrate, ciprofibrate, fenofibrate and gemfibrozil. They are not recommended as the sole drug therapy for women with heart disease for whom LDL cholesterol reduction is necessary. Fibrates are usually prescribed in twice-daily doses before breakfast and dinner. Side effects are rare, with gastrointestinal problems the most common. They may also increase the risk of cholesterol gallstones and can boost the effects of anticoagulants.

Combination drug therapy. If you haven't achieved your target LDL cholesterol level after three months on a single medication, your doctor may recommend adding a second one. Various combinations have been shown to be effective and safe. Lower doses of each individual drug can reduce the risk of side effects.

Preventing high cholesterol
Keeping to a low-saturated fat, low-cholesterol diet, being physically active and sticking to a healthy weight are all great ways to keep your levels down. But keeping your intake of cholesterol down will only win half the battle - and the lesser half at that. What's more important is to reduce your intake of saturated fat because it boosts your blood cholesterol level more than anything else.

Saturated fat is found mainly in food that comes from animals. Whole-milk dairy products such as butter, cheese, milk, cream and ice cream all contain high amounts. The fat in meat and poultry skin is loaded with saturated fat. A few vegetable fats, coconut oil, cocoa butter, palm kernel oil and palm oil are also high in saturated fat.

Polyunsaturated fats, such as safflower and corn oil, and monounsaturated fats, such as olive and canola oil, may lower LDL cholesterol levels. Polyunsaturated fats lower both HDL 'good' cholesterol and LDL cholesterol, while monounsaturated fats lower LDL. However, you should not try to boost your intake of these fats. Instead, concentrate on cutting back fat from all sources, but with an eye toward using these 'healthier' fats in place of saturated fats.

Eat more fat
Omega-3 fatty acids, which are found in fish, soybean and canola oil, appear to lower blood levels of LDL cholesterol and triglycerides. You may want to add fish to your diet once or twice a week and choose these oils over others.

Fish-oil supplements are also beneficial and are available on prescription to reduce a raised triglyceride level, as an alternative to a fibrate, and in addition to a statin.

Omega-6 fatty acids such as linoleic acid, found in corn, soybean and safflower oil have also received widespread publicity for cholesterol-lowering effects, but again, the best advice is to avoid adding any fats to your diet.