Like all of the body’s organs and tissues, your heart needs a constant supply of oxygen-rich blood to function normally.
Blood is supplied to the heart by two large blood vessels that are known as the left and right coronary arteries. Stable angina is most commonly caused when the coronary arteries become narrow and hardened (atherosclerosis), which restricts the blood flow to the muscles of the heart.
Stable angina is essentially a supply and demand problem. When you are at rest, the muscles of your heart only need a relatively small supply of blood, so you will not experience any symptoms. However, when you exercise or feel stressed, your heart muscles have to work harder and the demand for blood increases.
Due to the narrowed coronary arteries, the required amount of blood is unable to reach the heart in time, which means that the demand for blood outstrips the supply, triggering the symptoms of angina.
Unstable angina
One of the underlying causes of atherosclerosis is a build-up of fatty deposits, known as plaques, in the arteries. If the plaques rupture (split) it will interfere with the normal flow of blood and cause a blood clot to form.
A blood clot can quickly grow, blocking one of the coronary arteries and significantly reducing the blood supply to the heart, triggering the symptoms of unstable angina.
Risk factors
Anything that causes the coronary arteries to narrow is a risk factor for both stable and unstable angina. For example:
These individual risk factors can often be inter-related. They are explained below in more detail.
High blood pressure
Your arteries are designed to pump blood at a certain pressure. If that pressure is exceeded, the artery walls will be damaged. High blood pressure can be caused by:
- being overweight
- drinking excessive amounts of alcohol
- smoking
- stress
- a lack of exercise
For reasons that are not fully understood, high blood pressure is more common among people of Afro-Caribbean and south Asian (Indian, Pakistani and Bangladeshi) origin.
A tendency to develop high blood pressure also often runs in families. This is known as a genetic predisposition.
Read more about how to prevent high blood pressure.
High-fat diet and cholesterol
Cholesterol is a type of fat that is essential for the functioning of the body. It helps produce hormones, protects nerve endings and makes up cell membranes (the walls that protect individual cells). There are two main types of cholesterol:
- low density lipoprotein (LDL) - is mostly made up of fat, plus a small amount of protein; this type of cholesterol can block your arteries so it is often referred to as ‘bad cholesterol’
- high density lipoprotein (HDL) - is mostly made up of protein, plus a small amount of fat; this type of cholesterol can help reduce a blockage in your arteries so it is often referred to as ‘good cholesterol’
Most of the cholesterol that the body needs is manufactured by the liver. However, eating foods that are high in saturated fat results in cholesterol being broken down into LDL (bad cholesterol).
Read more about how changes to your diet can help you reach and maintain a healthy weight, as well as lowering your cholesterol and blood pressure.
Lack of exercise
A lack of regular exercise can raise your blood pressure and increase your risk of developing type 2 diabetes. Both of these factors increase your risk of developing angina.
Alcohol
Drinking excessive amounts of alcohol will also increase your risk of developing angina.
Excessive drinking is defined as regularly exceeding the recommended daily allowance of three to four units of alcohol a day for men and two to three units a day for women. A unit of alcohol is approximately half a pint of normal strength lager, a small glass of wine or a single measure (25ml) of spirits.
Regularly exceeding the recommended alcohol limits will raise your blood pressure and your cholesterol level, both of which are risk factors for angina.
Smoking
Smoking can damage the walls of your arteries. If your arteries are damaged by smoking, blood cells called platelets will form at the site of the damage in an attempt to repair it. This can cause your arteries to narrow.
Smoking also decreases your blood's ability to carry oxygen around your body, which increases the chances of a blood clot occurring.
Diabetes
If you have poorly controlled diabetes, the excess amount of glucose in your blood can damage the walls of your arteries.
Age
Arteries tend to get narrower over time. Therefore, the older you are, the more likely it is that your arteries will have narrowed, increasing your risk of developing angina.
Family history
Heart disease can run in families, so if you have a first degree relative (mother, father, brother or sister) with a history of heart disease or angina, your risk of developing angina is increased.
