Almost all cases of coronary heart disease (CHD) are due to atherosclerosis – either directly or indirectly. There are a variety of factors, often acting together, which are associated with an increased risk of atheroma, and thus of CHD.
Some of these factors are beyond our control – such as age and gender – but others can be manipulated to influence the outcome. Such factors include medical conditions (e.g. hypertension) and lifestyle factors (e.g. diet or physical activity).
Known risk factors for CHD include:
1. Family history
This is an important, independent risk factor for CHD, especially in younger persons (particularly if one parent has had documented, premature CHD – i.e. a father who had CHD before the age of 55 or a mother who had CHD before the age of 65).
Family history nearly doubles the risk of developing CHD. And it is a risk factor that cannot be modified.
2. Gender and age
Men are at a slightly increased risk of developing CHD, as are older persons. But women and younger people are by no means unaffected. One in three men and one in four women suffer from CHD in South Africa.
Gender and age are, of course, risk factors that cannot be changed.
3. Blood lipids
Total blood cholesterol level is an established risk factor for CHD, and the risk increases progressively with the value.
Of importance is not only the total, but also the levels of sub-fractions such as LDL ("bad") and HDL ("good") cholesterol. The ideal pattern of cholesterol for a person with no known CHD risk factors is:
- normal total cholesterol: <5
- normal triglycerides: <1.7
- low LDL: <3
- high HDL: >1
Very high total cholesterol, or an abnormal pattern, can result in cholesterol plaques being deposited in coronary arteries, leading to angina and heart attack. Blood clots tend to form on top of these plaques, and this can cause further, or even total, obstruction of the artery. If a piece of this clot breaks off and is carried into the circulation to arteries in the brain, this can cause a stroke.
Normalising the lipid profile can significantly delay the onset and complications of CHD.
High blood pressure is called “the silent killer” because, by itself, it seldom causes any symptoms. In the long term though, persistently raised pressure in arteries increases the workload of the heart, and can accelerate the rate of atheroma formation due to raised cholesterol.
Strict control of blood pressure – the ideal is 120/80 – drastically reduces the risk of heart disease and stroke.
5. Cigarette smoking
This is an important, reversible risk factor. The risk of a heart attack is increased six times in women, and three times in men, who smoke 20 cigarettes per day, compared to those who have never smoked.
The risk is immediately reduced when a person stops smoking. Smoking cessation also has an instant, positive effect on the lungs. After 15 years of not smoking, the risk of heart disease is reduced to that appropriate for the person’s age plus other remaining risk factors.
Statistically, having diabetes brings the same risk of heart disease as that for a person who has already had a full-blown heart attack. In medical terms, diabetes is thus the risk equivalent of a myocardial infarct.
In addition to this, diabetics have a greater burden of other atheroma-inducing risk factors, such as hypertension, obesity, raised cholesterol and triglyceride levels, and increased risk of clotting.
7. Obesity and related factors
Obesity aggravates all other risk factors which may already be present, and physical inactivity further increases the risk.
Certain persons who have a syndrome of abdominal obesity, hypertension, diabetes and dyslipidaemia are labelled as having the metabolic syndrome. This brings a marked increase in the risk of CHD due to the combination of the different problems, each with its own risk profile.
8. Other factors
- Chronic kidney disease, and even moderate impairment, increases the risk of CHD.
- Post-menopausal women have an increased risk of CHD, but there isn't enough evidence to advocate oestrogen replacement purely as a measure to prevent CHD.
- Depression, anger and stress have all been linked to CHD, but are difficult to measure. It is suggested that these problems act by increasing other known risk factors such as hypertension and excess alcohol consumption.
Other possible risk factors for CHD:
There are a number of conditions which are statistically linked to the incidence of CHD. However, it hasn't been proved that they're causative factors. These include:
- High resting pulse rate.
- High blood homocysteine levels. However, research shows that lowering these levels doesn't protect against CHD.
- Hyperuricaemia (gout).
- Acute or chronic infection.
- Collagen diseases such as systemic lupus erythematosus (SLE) or rheumatoid arthritis.
- Air pollution. Fine particles such as those in diesel fumes have been implicated as theoretical triggers for CHD, but no convincing proof has yet been found.
- Antioxidants. However, use of antioxidant supplements has shown no clear benefit in reducing CHD.
Reviewed by Dr A.G. Hall (B.Soc.Sc.(SW), MB,Ch.B)