In this article

What is CHD? What are the symptoms of CHD? Other CHD symptoms

Heart attack? What causes CHD?

Other heart diseases Who's at risk?

Your weight

Even being moderately overweight increases your risk of CHD. This may be because you're more likely to develop diabetes, have raised blood cholesterol levels and high blood pressure. It's also more difficult to be physically active if you are carrying excess pounds.

Your shape

Apple-shaped people who carry fat around their waist are more at risk of CHD than pear-shaped people who carry excess weight around their hips. The tendency to a particular shape is largely inherited, so if one or both your parents are 'apples', it's worth taking particular care over diet and exercise to lose excess fat.

Your activity levels

Watching too much television and taking the car instead of walking both increase your risk of obesity and, consequently, your risk of CHD. Lack of activity also decreases your body's ability to extract oxygen from your blood, weakens your bones (leading to a risk of osteoporosis) and your muscles, and encourages high cholesterol levels.

Blood pressure

Blood pressure is the force of blood in your arteries and is determined by how hard your heart works and the health of your blood vessels.

High blood pressure (or hypertension) is when the pressure is persistently higher than it should be (above 140/90 in healthy individuals), causing increased strain on your arteries. Over time, the force of the blood flowing through the arteries causes the smooth lining to roughen and the walls to become thicker. This causes the arteries to narrow and become less elastic.

Because high blood pressure often has no symptoms it's important to have your blood pressure checked regularly, so you can take steps to reduce it if it's raised, before it leads to heart disease or a stroke.

Your cholesterol

Cholesterol is a waxy, fatty substance made by your liver. It's also present in some foods such as animal fats, eggs and shellfish. Your body needs some cholesterol to produce hormones and to produce the bile needed to digest fat. It's also the main ingredient of cell membranes.

Cholesterol travels around your bloodstream in special proteins called lipoproteins. There are two types: low-density lipoproteins or LDL (also known as 'bad cholesterol'), which carries cholesterol to your body's cells, and high-density lipoproteins or HDL (also known as 'good cholesterol'), which helps clear excess cholesterol from your arteries and carries it back to your liver to be destroyed.

If you have high levels of LDL and low levels of HDL you're more at risk of heart disease.

Factors predisposing towards unhealthy cholesterol levels include eating a diet high in saturated (animal) fats and/or transfats found in processed foods, being overweight, drinking too much alcohol and not doing enough exercise.

Cholesterol and atherosclerosis

Atherosclerosis, a build up of fatty materials within the walls of arteries, is set off when LDL cholesterol undergoes a chemical reaction called oxidation - the same reaction that causes butter to go rancid.

Oxidation is caused by free radicals - harmful molecules produced as a result of the normal metabolism that occurs within the body.

Free radicals also come from ionising radiation from the sun's rays, ozone and nitrous oxide from car exhausts and cigarette smoke. These free radicals contribute to atherosclerosis that results in heart disease.

Smoking

Smoking increases your risk of having a heart attack two-fold or three-fold. In fact, if you're under 50 and smoke, you're five times more likely to die of CHD than a non-smoker.

There are several reasons for this. Nicotine triggers the release of the stress hormone adrenalin, which raises your heart rate and blood pressure, increasing your heart's need for oxygen.

Carbon monoxide, found in tobacco smoke, displaces oxygen from your blood cells, depriving your heart of oxygen. Other chemicals in cigarette smoke trigger the release of free radicals, the harmful molecules involved in the development of atherosclerosis.

Smoking also decreases the level of ‘good fats’ in the body, such as HDL, and may increase blood pressure and make the blood more likely to form clots. Smoking is particularly dangerous when other risk factors such as diabetes or high blood pressure are also present.

Raised homocysteine levels

Some people with CHD have raised levels of a substance called homocysteine, an amino acid (one of the building blocks that make up protein) that your body uses to build tissues.

Raised homocysteine levels are thought to damage the lining of arteries, a crucial step in the development of atherosclerosis. They've been found to be a factor in the oxidation of cholesterol and also appear to increase blood clotting.

Smoking and inactivity lead to raised homocysteine levels, and low levels of folic acid and vitamins B6 and B12, in particular, have also been linked to this.

However, recent studies have failed to show convincingly that high homocysteine levels are associated with an increased risk of CHD, and there's no proof that efforts to lower homocysteine (such as taking folic acid supplements) can protect from atherosclerosis.

Because the evidence remains uncertain, experts are reluctant to designate a raised homocysteine level as a risk factor for CHD until further research provides a clearer answer.

This article was last medically reviewed by Dr Trisha Macnair in March 2007.
First published in June 2001.