What is cholesterol?
Cholesterol is found in every cell of the body and has important natural functions. It is manufactured by the body but can also be taken in from food. It is waxy and fat-like in appearance.
Cholesterol is oil-based and so does not mix with the blood, which is water-based. It is therefore carried around the body in the blood by lipoproteins.
The parcels of cholesterol are carried by two types of lipoprotein:
- Low-density lipoprotein (LDL – cholesterol carried by this type is known as ‘bad’ cholesterol)
- High-density lipoprotein (HDL – cholesterol carried by this type is known as ‘good’ cholesterol).
Cholesterol has four main functions, without which we could not live. It:
- Contributes to the structure of cell walls
- Makes up digestive bile acids in the intestine
- Allows the body to produce vitamin D
- Enables the body to make certain hormones.
What causes high cholesterol?
High cholesterol is a major risk factor for coronary heart disease, a cause of heart attacks, and reducing blood lipid levels lowers the cardiovascular risk.
High levels of LDL lead to a build-up of cholesterol in the arteries, whereas HDL carries cholesterol to the liver for removal from the body. A build-up of cholesterol forms part of the process that narrows arteries, called atherosclerosis, in which plaques form and cause restriction of blood flow.
Two types of cause lead to high cholesterol levels – modifiable and non-modifiable risk factors. The major two risk factors are highly modifiable – something can be done to change them:
- Exercise and weight.
Limiting intake of fat in the diet helps manage cholesterol levels, limiting foods, in particular, that contain:
- Cholesterol (from animal foods, such as egg yolks, meat and cheese)
- Saturated fat (found in some meats, dairy products, chocolate, baked goods, and deep-fried and processed foods)
- Trans fat (found in some fried and processed foods).
Being overweight or obese can lead to higher blood LDL levels so exercise can help manage this risk factor.
The primary causes of high cholesterol are genetic – very high LDL levels are found in the inherited condition familial hypercholesterolemia.
Abnormal cholesterol levels may also be secondary to the following:
- Liver or kidney disease
- Polycystic ovary syndrome
- Pregnancy and other conditions that increase levels of female hormones
- Underactive thyroid gland.
- Drugs that increase LDL cholesterol and decrease HDL cholesterol (progestins, anabolic steroids and corticosteroids).
Fast facts on cholesterol
Here are some key facts about cholesterol. Find more detail and supporting information in the article.
- Cholesterol is an essential substance that is produced by the body but is also available from foods.
- The greatest risk factors for high cholesterol are modifiable lifestyle choices – diet and exercise.
- High cholesterol levels can be inherited with the genetic condition, familial hypercholesterolemia.
- Having high cholesterol does not produce any symptoms.
- Cholesterol levels should be blood-tested once every five years.
- First-line ways to reduce cholesterol involve lifestyle changes.
- If lifestyle changes are unsuccessful or cholesterol levels are very high, lipid-lowering drugs such as statins may be prescribed.
- High cholesterol levels are an important contributor in the calculation of an individual’s risk of having a heart attack within the next ten years.
Signs and symptoms of high cholesterol
Having high cholesterol levels, while a risk factor for other conditions, does not itself present any signs or symptoms. Unless routinely screened through regular blood testing, high cholesterol levels will go unnoticed and could present a silent threat of heart attack or stroke.
Cholesterol tests and diagnosis
High cholesterol can only be diagnosed by blood testing. Doctors’ guidelines state that everyone over the age of 20 years should have their cholesterol levels checked once every five years.
The cholesterol test is done after a period of fasting – no food, drink or pills for 9 to 12 hours – to enable an accurate reading of LDL cholesterol from the blood test. The screening also gives information about total cholesterol, HDL cholesterol and triglyceride levels.
The guidelines set cholesterol levels that help determine the individual heart risk, as follows:
- Optimal: less than 100 mg/dL
- Near-optimal: 100 to 129 mg/dL
- Borderline high: 130 to 159 mg/dL
- High: 160 to 189 mg/dL
- Very high: 190 mg/dL and above.
Guidance is also set out for the other measures in the lipid profile:
- Desirable: less than 200 mg/dL
- Borderline high: between 200-239 mg/dL
- High: 240 mg/dL or above.
- Low: below 40 mg/dL
- High: 60 mg/dL or above.
Treatment and prevention of high cholesterol
Four changes to lifestyle are recommended for all people with high cholesterol levels – including those receiving drug treatment – in order to reduce the risk of coronary heart disease and heart attack:
- Eat a ‘heart-healthy diet’ (for example, use low-fat toppings and sauces, and avoid foods high in saturated fat; eat vegetables, fruits and fiber-rich whole grains)
- Take regular exercise
- Avoid smoking
- Keep a healthy weight.
Ten-year risk of a heart attack
Cholesterol levels play a major part in an individual’s risk of having a heart attack within the next ten years. The National Heart, Lung and Blood Institute provide an online calculator of cardiovascular risk. Using research evidence, it weighs the risk dictated by these factors:
- Cholesterol levels
- Smoking status
- Blood pressure.
Monitoring the ten-year risk according to data from the Framingham Heart Study, which continues today, helps in the management of lifestyle and other measures to reduce cholesterol levels, and so cut the chances of cardiovascular disease leading to heart attack or stroke.