Cholesterol

Introduction

Cholesterol is a body fat, or lipid. It is an important part of a healthy body, being a building block for steroids such as the sex hormones, and the hormones of the adrenal cortex. It is also the basis of the body’s manufacture of bile salts.

Cholesterol is mainly produced in the liver, and has a further use in forming cell membranes and other needed tissues.

Cholesterol is carried in the blood by special molecules called lipoproteins. The three main forms of lipoproteins are:

Low density lipoprotein (LDL). This is often known as ‘bad cholesterol’ and is thought to promote arterial disease. It carries cholesterol from the liver to the cells and can cause harmful cholesterol build-up if there is too much to be used up by the cells.  

High density lipoprotein (HDL). This is often referred to as 'good cholesterol', and may oppose arterial disease. It takes cholesterol away from the cells and back to the liver, where it's either broken down or excreted. 

Triglycerides.

The amount of cholesterol present in the blood can range from 3.6 to 7.8 mmol/litre. A level above 6 mmol/litre is regarded as high, and is a risk factor for arterial disease. Government advice recommends a target cholesterol level of under 5, but on average men in England have a level of 5.5, and women a level of 5.6.

Evidence strongly indicates that high cholesterol levels can cause narrowing of the arteries (atherosclerosis), heart attacks, and strokes. The risk of coronary heart disease also rises as blood cholesterol levels increase. When other risk factors, (such as high blood pressure and cigarette smoking), are present, this risk increases even more.

In atherosclerosis, deposits of fatty substances, cholesterol, cellular waste products, calcium and other substances build up in the inner lining of an artery. This build up is called plaque, and it usually affects arteries of small and medium size. The flow of blood through these arteries is restricted as the inside diameter is reduced. Clotting of the blood, which often happens in the coronary arteries during a heart attack, is most likely to develop when arterial walls are roughened by such plaques.

Symptoms

High cholesterol levels is not a disease in itself, but it is linked to other serious conditions. A large amount of cholesterol in the blood, together with triglycerides, can increase your risk of developing coronary heart disease.

The cause of coronary heart disease is a narrowing of the arteries that supply the heart with blood. Fatty material, such as cholesterol, is deposited in the arteries, causing them to become clogged, which is known as atherosclerosis. High cholesterol levels may only be revealed through the symptoms of atherosclerosis, which include the following:

Blood clots and ruptured blood vessels, sometimes resulting in a stroke.

Angina, caused by narrow coronary arteries in the heart ruptured plaques. This causes coronary thrombosis, and may lead to heart failure if a significant amount of heart muscle is damaged. 

Leg pain on exertion. This is experienced due to atherosclerosis in the arteries that supply the lower limbs.

High cholesterol is also linked to diseases such as reduced metabolism (due to thyroid hormone problems, for example), kidney diseases, and diabetes and alcohol abuse.

Causes

Atherosclerosis and related heart disease, along with conditions such as diabetes mellitus, are on the increase in the Western world. Research has shown that there may be a link between these diseases and high blood cholesterol, and between high blood cholesterol and the amount of fat in the diet. People with high levels of cholesterol and trigylcerides, and low levels of HDL are particularly at risk. Foods high in cholesterol and fat increase cholesterol levels in the body, and include:

• Meats
• Poultry
• Fish
• Seafood
• Dairy products.

When saturated solid fats, such as butter, are added to the diet, the amount of cholesterol in the blood increases.

Take the 5-a-day fruit and veg test

The body can make all the cholesterol it needs without having to take in any additional cholesterol from the food we eat. Blood cholesterol levels are affected by the speed at which your body makes LDL cholesterol and disposes of it. This level is affected by:

• Heredity;
• Weight;
• Physical activity/ exercise;
• Age and sex;
• Alcohol consumption; and
• Stress.

Diagnosis

A blood sample is taken to test for the level of cholesterol, LDL-cholesterol, HDL-cholesterol and triglyceride in your blood. For this test to be accurate you should fast for 12 hours before the test. You should not eat or drink anything except for clear fluids such as water or tea or coffee without milk. The best time to do the test is therefore probably in the morning after a nights sleeping.

The cholesterol ratio should not be taken on its own as a predictor of the risk of heart attack or stroke. Smoking, body mass index (weight related to height), blood pressure, diabetes and any ECG (electrocardiogram) abnormalities are equally important.

Blood cholesterol checks should be done in people with:

A family history of cholesterol disorders

A history of many heart attacks in the family, especially if some of these have occurred at a young age

• Obesity
• Diabetes
• Thick yellow patches (xanthomas) around the eyes or elsewhere on the skin. (These are cholesterol deposits and can often be seen in some patients with inherited or familial cholesterol.)
• High blood pressure
• Acute inflammation of the pancreas (acute pancreatitis).

Some people may have a high blood cholesterol level, but still have a low cardiovascular risk due to the absence of other risk factors, and a family medical history that is free from coronary disease. It is also worth bearing in mind that cholesterol levels rise slightly with age, and women often have a higher DL-cholesterol level than men. Women over the age of 45 and men over the age of 35 should have their blood cholesterol levels checked periodically.

Treatment

The first level of treatment is a trial of a low-fat diet and exercise. If, after a few months, cholesterol levels have not dropped, then cholesterol-lowering drug treatment is sensible, whatever the cause of the raised blood cholesterol.

People who naturally have abnormally high levels of cholesterol (especially low-density lipoproteins) can reduce their risk of heart attack by lowering their blood cholesterol. This can be done by following a diet low in saturated fats, and by using cholesterol-lowering drugs.

Complications

High cholesterol levels can be exacerbated by additional medical conditions. Medical problems such as an underactive thyroid gland, an overactive pituitary gland, liver disease or kidney failure can contribute to high cholesterol levels. Some people have inherited disorders that prevent their bodies from properly using and eliminating fats. This allows cholesterol to build up in the blood.

The major complications of raised blood cholesterol are heart attacks, strokes and arterial disease. The risks of all of these are increased if you:

• Are overweight, 
• Smoke, 
• Have high blood pressure,
• Have a strong family history of these problems, 
• Are diabetic

Prevention

The best way to prevent high blood cholesterol is to eat a healthy balanced diet low in animal fats.

Take the 5-a-day fruit and veg test

If there is a family history of cholesterol problems, a blood test is advisable, as treatment may be necessary. If the person is very overweight, weight loss will also help reduce the cholesterol level. Regular exercise can help weight loss, and is also beneficial.

If liquid, unsaturated fats or oils, (particularly the polyunsaturated type), replace solid fats in the diet, the amount of cholesterol decreases. Foods high in unsaturated fats include olive oil and oily fish. Current thinking is that the traditional Mediterranean diet, with its emphasis on raw olive oil in many foods and low animal-fat content, is one of the best there is for cardiovascular health (the health of the heart and blood circulation).

Healthcentral 2005

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