Sunday, January 18, 2015

High cholesterol

IQWIG. Germany: Many people worry about their cholesterol levels because high blood cholesterol can increase the risk of cardiovascular disease.
People are considered to have high cholesterol (“hypercholesterolemia”) when certain levels are exceeded. But having high cholesterol levels is not a medical condition in itself. And there are different opinions about when cholesterol levels are too high.

It is important to remember that hypercholesterolemia is just one of many risk factors for cardiovascular disease. This means that cholesterol levels alone tell us little about a person’s risk.
This information is about high cholesterol levels in people who do not already have cardiovascular disease.

Symptoms

High cholesterol does not in itself cause any symptoms. But if someone has high cholesterol levels over many years, their risk of cardiovascular disease – such as angina, heart attacks and strokes – might be higher than normal for their age. So it can be a good idea for people who have high cholesterol to do something about it.

Causes

Your cholesterol levels are mainly influenced by two factors: the genes you inherited from your parents and your lifestyle.
Genes play a big role in some people, who then might even have very high cholesterol in childhood. This is known as familial hypercholesterolemia. There are various types of this kind of problem, which can sometimes be a serious health risk.
In most people, though, genes only play a fairly small role. Their cholesterol levels are mainly influenced by lifestyle factors such as their diet and exercise habits. This kind of high cholesterol is called non-familial hypercholesterolemia.
Sometimes people’s cholesterol levels increase because of a medical condition they have, such as an underactive thyroid gland. Taking certain medications can also make your cholesterol levels go up somewhat. To try to rule out these causes, doctors ask questions about people's medical history and other possible causes of high cholesterol.

Risk factors

As a general rule, the higher the cholesterol levels, the higher the risk of cardiovascular disease. But cholesterol is not the only risk factor. Many other things can have an influence – both positive and negative. The risk of cardiovascular disease can only be properly assessed if all the factors are considered together.
People’s individual risk can be determined with the help of special tables or computer programs, sometimes called risk calculators. This is best done together with a doctor. Various pieces of information about risk factors are needed to calculate the risk. The main risk factors include:
  • Age: The risk of cardiovascular disease increases with age.
  • Sex: Men are at higher risk than women.
  • Family history: People are at greater risk if they have a brother or father who had a heart attack or stroke before the age of 55, or if they have a sister or mother who had a heart attack or stroke before the age of 65.
  • Smoking: Smoking increases the risk more than, for instance, moderately high cholesterol levels.
  • High blood pressure: High blood pressure puts extra strain on the heart and circulation.
  • Type 2 diabetes: People who have type 2 diabetes have a greater risk than people of their age who do not have diabetes.
  • Cholesterol levels: High total cholesterol, high LDL cholesterol (“bad cholesterol”) and low HDL cholesterol (“good cholesterol”) are unfavorable.

When people’s risk of cardiovascular disease is assessed, it is generally expressed as the likelihood of having a stroke or heart attack within the next ten years. The following examples of two women (Veronica and Isabel) and two men (Fred and Carl) might help make it clearer why it is so important to consider all of the different risk factors together.



Table: Influence of different risk factors in women
Risk factor Veronica Isabel
Total cholesterol High(260 mg/dL) High (260 mg/dL)
HDL cholesterol Slightly low (44 mg/dL) Slightly low (44 mg/dL)
Age 50 years old 50 years old
Family history No Father had a heart attack before the age of 55
Smoking No Yes
Blood pressure Slightly high(145/90 mmHg)  Slightly high (145/90 mmHg)
Type 2 diabetes No No
Risk of heart attack or stroke within the next ten years 4 % 18 % 
Table: Influence of different risk factors in men
Risk factor Fred Carl
Total cholesterol High (260 mg/dL) High (260 mg/dL)
HDL cholesterol Slightly low (44 mg/dL) Slightly low (44 mg/dL)
Age 50 years old 50 years old
Family history No No
Type 2 diabetes No No
Smoking No Yes
Blood pressure Normal Very high (162/96 mmHg)
Risk of heart attack or stroke within the next ten years 11 % 33 %



Although all of the above four people have the same cholesterol levels, their individual risk of cardiovascular disease is very different. So cholesterol levels alone do not tell us much, and are therefore usually not a suitable basis for deciding whether or not to have cholesterol-lowering treatment.
By the way, the risk of a 50-year-old having a heart attack or stroke in the next ten years if they do not have any risk factors is 3% for men, and under 1% for women.

Diagnosis

Cholesterol does not dissolve in water (or blood). To be able to transport it in the blood, our bodies pack cholesterol into tiny parcels, together with various proteins and other things in our blood. Depending on what else is packed into those parcels, the parcels make up different kinds of cholesterol that can be distinguished between in a laboratory.
When looking at cholesterol levels, two different types are usually measured. The two types have different effects on cardiovascular health. In everyday language they are often referred to as “good” and “bad” cholesterol:
  • HDL cholesterol: HDL (high-density lipoprotein) cholesterol levels are a measure of the proportion of “good” cholesterol in your total cholesterol. Normal to high HDL cholesterol levels are associated with a lower risk of cardiovascular disease than low HDL cholesterol levels.
  • LDL cholesterol: LDL (low-density lipoprotein) cholesterol levels are a measure of the proportion of “bad” cholesterol. High LDL cholesterol levels are associated with a higher risk of cardiovascular disease.
The “total cholesterol” level is also measured. This describes how much cholesterol someone has in their blood overall. High total cholesterol levels tend to be unfavorable. It is best to measure total cholesterol and LDL cholesterol levels on an empty stomach. That is why people are asked to stop eating, and only drink water, twelve hours before being tested.
There is some disagreement about when cholesterol levels are “too high.” People are often diagnosed with hypercholesterolemia if their total cholesterol or LDL cholesterol is above the level that has been defined as “healthy.” HDL cholesterol levels below the threshold level are also considered to be unfavorable. Cholesterol levels can be measured in two different units: milligrams per deciliter (mg/dL) and millimoles per liter (mmol/L). The following levels are considered to be favorable in healthy people:
  • Total cholesterol: Levels below 200 mg/dL (5.2 mmol/L)
  • LDL cholesterol: Levels below 130 mg/dL (3.4 mmol/L)
  • HDL cholesterol: Levels above 40 mg/dL (1 mmol/L) in men and above 50 mg/dL (1.3 mmol/L) in women
How much of a health problem someone’s cholesterol levels are will depend on various factors, including exactly how high their cholesterol levels are and what other risk factors they have. It is not possible to assess a person’s individual risk of cardiovascular disease without taking this information into account.
Some experts criticize the use of pre-defined threshold levels because it means that a large number of people are considered to be “sick.” For example, according to a big study carried out by the Robert Koch Institute, 58% of all adults in Germany had a total cholesterol level of above 190 mg/dL in 2010.

Screening

In Germany, people who are covered by statutory health insurance funds are entitled to a general health check-up (“Gesundheits-Check-up”) every two years from the age of 35 onwards. The aim of this check-up is to detect early signs of cardiovascular disease, diabetes and kidney problems. It involves things like measuring your blood pressure and doing a blood test and a urine test. Total cholesterol is measured too.

Treatment

Treatment for high cholesterol is not only about lowering cholesterol levels. Instead, it is more about reducing a higher risk of cardiovascular disease to a normal level, if possible. Treatments can only be considered well tested if researchers have also looked at whether they actually prevent heart disease.
People who are at higher risk of cardiovascular disease are often advised to follow some general measures as part of their treatment. These include:
  • not smoking
  • reducing the amount of saturated fats in your diet
  • eating a “Mediterranean diet”
  • getting a lot of exercise
  • losing weight
Some of these measures can also have a positive effect on cholesterol levels.
Like with other kinds of treatment, when assessing medications it is not enough to look only at how they affect cholesterol levels. So far only one group of medications, known as statins, has been studied for the treatment of high cholesterol in people who have not had a heart attack, stroke or other cardiovascular disease. Statins have been shown to lower LDL cholesterol levels, but also seem to have other positive effects on blood vessels. There is some disagreement among researchers about whether the beneficial effects of statins are only due to their cholesterol-lowering ability or whether other factors play a role too.