GOOD CHOLESTEROL (HDL) AND BAD CHOLESTEROL (LDL)

 What is cholesterol?

Cholesterol is a lipid (fat chemical) that is made in the cells in your body. Many different cells make cholesterol but cells in the liver make about a quarter of the total. Although many foods contain cholesterol, it is poorly absorbed by the gut into the body. Therefore, cholesterol that you eat in food has little effect on your body and blood cholesterol level. A certain amount of cholesterol is present in the bloodstream. You need some cholesterol to keep healthy. Cholesterol is carried in the blood as part of particles called lipoproteins. There are different types of lipoproteins, but the most relevant to cholesterol are:

• Low-density lipoproteins carrying cholesterol - LDL cholesterol. This is often referred to as bad cholesterol. This is the one mainly involved in forming atheroma. Atheroma is the main underlying cause of various cardiovascular diseases (see below). The majority of cholesterol in the blood is LDL cholesterol, but how much varies from person to person.
• High-density lipoproteins carrying cholesterol - HDL cholesterol. This is often referred to as good cholesterol. This may prevent atheroma forming.

What are atheroma and cardiovascular diseases?

 Patches of atheroma are like small fatty lumps that develop within the inside lining of arteries (blood vessels). Atheroma is also known as atherosclerosis and hardening of the arteries. Patches of atheroma are often called plaques of atheroma.

Over months or years, patches of atheroma can become larger and thicker. So in time, a patch of atheroma can make an artery narrower. This can reduce the blood flow through the artery. For example, narrowing of the coronary (heart) arteries with atheroma is the cause of angina.

Sometimes, a blood clot (thrombosis) forms over a patch of atheroma and completely blocks the blood flow. Depending on the artery affected, this can cause a heart attack, a stroke, or other serious problems.

Cardiovascular diseases are diseases of the heart (cardiac muscle) or blood vessels (vasculature). However, in practice, when doctors use the term cardiovascular disease they usually mean diseases of the heart or blood vessels that are caused by atheroma.

In summary, cardiovascular diseases caused by atheroma include: angina, heart attack, stroke, transient ischaemic attack (TIA) - sometimes called mini-stroke - and peripheral vascular disease. In the UK, cardiovascular diseases are a major cause of poor health and the biggest cause of death.

What factors affect the blood level of cholesterol?

 To an extent your blood cholesterol level can vary depending on your diet. However, different people who eat the same diet can have different blood cholesterol levels. In general, however, if you eat less fatty food in your diet your cholesterol level is likely to go down.

In some people a high cholesterol level is due to another condition. For example, an underactive thyroid gland, obesity, drinking a lot of alcohol and some rare kidney and liver disorders can raise the cholesterol level.

 

In some people a very high level of cholesterol runs in the family, due to a genetic problem with the way cholesterol is made by the cells in your body. One example is called familial hypercholesterolaemia.

 

Risk factors

Everybody has some risk of developing atheroma which then may cause one or more cardiovascular diseases. However, some situations increase the risk. These include:

• Lifestyle risk factors that can be prevented or changed:
  • Smoking.
  • Lack of physical activity (a sedentary lifestyle).
  • Obesity.
  • An unhealthy diet - including eating too much salt.
  • Excess alcohol.
• Treatable or partly treatable risk factors:
  • High blood pressure (hypertension).
  • High cholesterol blood level.
  • High triglyceride (another type of fat) blood level.
  • Diabetes.
  • Kidney diseases that affect kidney function.
• Fixed risk factors - ones that you cannot alter:
  • A strong family history. This means if you have a father or brother who developed heart disease or a stroke before they were 55, or in a mother or sister before they were 65.
  • Being male.
  • An early menopause in women.
  • Age. You are more likely to develop atheroma as you get older.
  • Ethnic group. For example, people who live in the UK whose family came from India, Pakistan, Bangladesh, or Sri Lanka have an increased risk.
  However, if you have a fixed risk factor, you may want to make extra effort to tackle any lifestyle risk factors that can be changed.

Note: some risk factors are more risky than others. For example, smoking and a high cholesterol level probably cause a greater risk to health than obesity. Also, risk factors interact. So, if you have two or more risk factors, your health risk is much more increased than if you just have one.

For example, a middle aged male smoker who has high blood pressure and a high cholesterol level has a high risk of developing a cardiovascular disease, such as a heart attack, before the age of 60.

Cholesterol blood levels

The following levels are generally regarded as desirable:

• Total cholesterol (TC) - 5.0 mmol/L or less. However, about 2 in 3 adults in the UK have a TC level of 5.0 mmol/L or above.
• Low-density lipoprotein (LDL) cholesterol after an overnight fast: 3.0 mmol/L or less.
• High-density lipoprotein (HDL) cholesterol: 1.2 mmol/L or more.
• TC/HDL ratio: 4.5 or less. That is, your total cholesterol divided by your HDL cholesterol. This reflects the fact that for any given TC level, the more HDL, the better.

As a rule, the higher the LDL cholesterol level, the greater the risk to health.

However, your level of cholesterol has to be viewed as part of your overall cardiovascular health risk. The cardiovascular health risk from any given level of cholesterol can vary, depending on the level of your HDL cholesterol and on other health risk factors that you may have.

Calculating your cardiovascular health risk

A risk factor calculator is commonly used by doctors and nurses. This can assess your cardiovascular health risk. A score is calculated which takes into account all your risk factors such as age, sex, smoking status, blood pressure, cholesterol level, etc.

The calculator has been devised after a lot of research that monitored thousands of people over a number of years. The score gives a fairly accurate indication of your risk of developing a cardiovascular disease over the next 10 years. If you want to know your score, see your practice nurse or GP.

Who should have their cardiovascular health risk assessed?

Current UK guidelines advise that the following people should be assessed to find their cardiovascular health risk:

• All adults aged 40 or more.
• Adults of any age who have:
  • A strong family history of early cardiovascular disease. This means if you have a father or brother who developed heart disease or a stroke before they were 55, or in a mother or sister before they were 65.
  • A first-degree relative (parent, brother, sister, child) with a serious hereditary lipid disorder. For example, familial hypercholesterolaemia or familial combined hyperlipidaemia. These diseases are uncommon.

If you already have a cardiovascular disease or diabetes then your risk does not need to be assessed. This is because you are already known to be in the high-risk group.

What does the assessment involve?

A doctor or nurse will:

• Do a blood test to check your cholesterol and glucose (sugar) level.
• Measure your blood pressure and your weight.
• Ask you if you smoke.
• Ask if there is a history of cardiovascular diseases in your blood relations. If so, at what age the diseases started in the affected family members.

A score is calculated based on these factors plus your age and your sex. An adjustment to the score is made for certain other factors, such as strong family history and ethnic origin.

 

 

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