Cholesterol – Functions, reference ranges and treatment of high levels

What is cholesterol?

Cholesterol is a fat-like substance that is very important for the functioning of our body’s cells and for numerous metabolic processes. Among other things, the body needs cholesterol to produce bile acids, vitamin D and sex hormones.

Where is cholesterol found in the body?

Cholesterol is found almost everywhere in the body. To ensure that we always have sufficient cholesterol available, the body produces it itself, mainly in the liver. From there, it is transported via the blood to various tissues. We also absorb cholesterol from our diet. Cholesterol is not water-soluble. To enable it to be transported in the blood, it is bound to what are known as lipoproteins. The most important lipoproteins include LDL and HDL.

• HDL stands for ‘high-density lipoprotein’. HDL transports cholesterol from the tissues back to the liver, where it can be broken down. HDL is therefore often referred to as ‘good’ cholesterol.
• LDL stands for ‘low-density lipoprotein’ and transports cholesterol from the liver to the cells. This is why LDL cholesterol is also called ‘bad cholesterol’. If there is too much LDL cholesterol in the blood, it can build up on the walls of the blood vessels.

A high LDL cholesterol level increases the risk of atherosclerosis. A high HDL cholesterol level, on the other hand, does not automatically mean that the blood vessels are protected. The term ‘high cholesterol’ can refer to an elevated total cholesterol level or an elevated LDL cholesterol level. LDL cholesterol is particularly important for assessing cardiovascular risk.

When and how are cholesterol levels measured?

Atherosclerosis can increase the risk of heart attacks, strokes, kidney failure and other conditions. As elevated LDL cholesterol levels contribute to the development of atherosclerosis, cholesterol levels are routinely measured as part of blood tests, for example during a health check-up. In people with certain medical conditions or risk factors, cholesterol levels are monitored regularly. These include, amongst others:

• high blood pressure
• a previous heart attack or stroke
• diabetes mellitus
• obesity

How often check-ups are recommended depends on the individual’s risk and any potential treatment. For the test, a blood sample is taken and analysed in the laboratory. This usually involves measuring total cholesterol, LDL and HDL cholesterol, and triglycerides. In Austria, the values are usually given in milligrams per decilitre (mg/dl).

What are normal cholesterol levels?

The target cholesterol levels depend primarily on an individual’s risk of cardiovascular disease. Factors such as age, gender and pre-existing conditions play a role here. The following cholesterol levels serve as a general guide for adults:

• Total cholesterol: below 190 mg/dl (approx. 4.9 mmol/l)
• LDL cholesterol: below 116 mg/dl (approx. 3.0 mmol/l)
• HDL cholesterol: men: over 40 mg/dl (approx. 1 mmol/l); women: over 50 mg/dl (approx. 1.3 mmol/l)

These figures are not universally applicable treatment targets. For example, anyone who has already had a heart attack requires a significantly lower LDL level. A high HDL level alone, however, does not offer reliable protection against cardiovascular disease. For a medical assessment, the overall picture is what counts: in addition to cholesterol levels and triglycerides, factors such as age, blood pressure, smoking, diabetes and existing cardiovascular diseases are taken into account.

When are cholesterol levels too low, and when are they too high?

An unusually low cholesterol level is less common than elevated levels. Possible causes include:

• Malnutrition
• Cirrhosis of the liver
• Hyperthyroidism
• certain lipid metabolism disorders

Unexpectedly low levels should be investigated by a doctor. However, an LDL cholesterol level that has been specifically lowered by medication is not automatically ‘too low’. Low LDL levels are particularly desirable in cases of high cardiovascular risk. An elevated cholesterol level is also known as hypercholesterolaemia. A distinction is made between primary and secondary hypercholesterolaemia:

• Primary hypercholesterolaemia is genetic (familial hypercholesterolaemia) and leads to persistently elevated cholesterol levels.
• Secondary hypercholesterolaemia is more common than the primary form and is caused by other medical conditions or lifestyle factors. The diagnosis may relate to both total cholesterol and LDL cholesterol.

Possible causes of secondary hypercholesterolaemia include:

• chronic kidney disease
• diseases of the liver and bile ducts
• nephrotic syndrome
• hypothyroidism
• (poorly controlled) diabetes mellitus
• Obesity
• insufficient exercise and an unbalanced diet
• certain medicines, such as corticosteroids or diuretics

Is it possible to lower cholesterol levels without medication?

Above all, lifestyle changes can help to lower cholesterol levels without medication. These include:

• a balanced diet low in saturated fats and high in unsaturated fats
• sufficient exercise
• a healthy body weight
• giving up smoking
• limiting alcohol consumption

Not all of these measures directly lower LDL levels. Giving up smoking, for example, primarily protects the heart and blood vessels. Whether lifestyle changes alone are sufficient depends on the level of the values and your personal cardiovascular risk. The polyunsaturated fatty acids linoleic acid (omega-6) and alpha-linolenic acid (omega-3) cannot be produced by the body itself and must be obtained from food. They are important for metabolism and the formation of cell membranes. Replacing saturated fatty acids with unsaturated ones can help lower your LDL cholesterol levels. Saturated fatty acids should be limited, and trans fatty acids avoided where possible. A high intake can raise LDL cholesterol levels and total cholesterol.

What should you eat – and what should you avoid – if you have high cholesterol?

If your cholesterol levels are high, you should avoid foods containing large amounts of saturated fatty acids, or eat them in smaller quantities. These fatty acids are found particularly in animal-based foods. Especially if your cholesterol levels are high, you should eat the following foods less frequently:

• high-fat dairy products
• high-fat meat and sausage products
• deep-fried foods
• processed foods such as baked goods and ready meals with a high content of saturated fatty acids

Instead, unsaturated fatty acids should be included in the diet. These are found, amongst other things, in various cooking oils as well as in certain fish and nuts. A low-cholesterol diet consists mainly of:

• plenty of fruit and vegetables
• wholemeal cereal products
• pulses such as lentils, beans and chickpeas
• lean meat and fish
• unsalted nuts and vegetable oils such as rapeseed and olive oil

Even small but sustained changes to your diet can have a very positive effect on your cholesterol levels and your health.

High cholesterol – drug treatment

If lifestyle changes are not sufficient to lower LDL cholesterol levels, medication may also be necessary. The decision to prescribe medication does not depend solely on cholesterol levels, but also on individual risk factors. These include an individual’s risk of atherosclerosis and its associated complications. Statins (cholesterol synthesis enzyme inhibitors) are usually prescribed first. They inhibit cholesterol production in the liver, thereby primarily lowering LDL cholesterol levels. If statins alone are not sufficiently effective, they can be supplemented with other medicines. These include, for example, the cholesterol absorption inhibitor ezetimibe, which reduces the absorption of cholesterol in the gut. Another option is PCSK9 inhibitors such as alirocumab and evolocumab. These block the enzyme PCSK9, which is involved in cholesterol metabolism. PCSK9 inhibitors are primarily used in cases of hereditary lipid metabolism disorders or when other treatments have not been sufficiently successful in lowering LDL cholesterol. The choice of medication or combination therapy depends on many factors and is decided on an individual basis for each patient. The decision is based on cholesterol levels, any underlying conditions, the individual’s risk of cardiovascular disease, and how well the patient tolerates the medication.