What is cholesterol, where does it come from?

Cholesterol has gained itself a bad name in recent years because of the harmful effects high blood levels of it can have on the heart and within the wider cardiovascular system; however, it is an essential building block and an essential part of your body's metabolism.

Cholesterol - a white, waxy substance - has a crucial role in the production of steroid hormones (eg, testosterone, oestrogen) and vitamin D, but its largest use is as a vital building block of the body's cells.

Given the important roles it has, it is probably not surprising that the body has the ability to manufacture its own supply of cholesterol - the body manufactures the majority (70-80%) of the cholesterol in your system. The fact that cholesterol also comes from our diet is generally well known.

Two sources of cholesterol

The two sources of cholesterol mean there are two main contributors to the cholesterol levels in your bloodstream.

1) Manufacture within the body:

• liver (the main production site)
• intestine
• other organs

2) Diet.

Cholesterol manufacture by the body adapts to the amount of cholesterol absorbed from your diet. So a high cholesterol diet will tend to lower the body's own cholesterol production. This is a complex balancing system that is not fully understood.

How does the body remove cholesterol?

The body removes cholesterol by incorporating it into bile salts in the liver. These are then stored in the gallbladder as liquid bile, which is released into the intestine to help make other fats soluble so they can be digested. A large proportion of the cholesterol in bile salts will, however, be reabsorbed from the digestive tract back into the bloodstream, and back to the liver, along with cholesterol from the diet.

What are the types of cholesterol?

If your doctor has told you have high cholesterol, and on your test results you see there may be three or four cholesterol results plus others you've never heard of… you are entitled to be confused.

Put simply, cholesterol will not dissolve in water, or blood, as it is fatty. It needs to be carried around the body in the bloodstream - to and from the liver, to cells around the body - by water-soluble molecules known as lipoproteins. Cholesterol is carried by different types of lipoproteins, depending on whether cholesterol is being transported to or from the liver, and it is these that are measured.

The different lipoproteins are characterised by how dense they are:

• VLDL; very low density lipoproteins
• LDL; low density lipoproteins (the "bad" form of cholesterol, responsible for narrowing and blocking arteries)
• HDL; high density lipoproteins (the "good" form, responsible for returning surplus cholesterol back to the liver).

Your Total Cholesterol measurement includes all of these, and you may also be given your Triglycerides measurement (another important fat) and your "Total Cholesterol to HDL ratio", which should be under 4.

New Zealand Guidelines for cholesterol measurements

For most patients:

• Total Cholesterol - below 4.0 mmol/L
• LDL Cholesterol - below 2.0 mmol/L
• HDL Cholesterol - above 1 mmol/L
• Total Cholesterol: HDL ratio - below 4
• Triglycerides - below 1.7 mmol/L.

NOTE: Patients who have had heart surgery (CABG: Coronary artery bypass graft) - will be given lower target figures for Total Cholesterol and LDL Cholesterol by their doctor.

Ways to improve your blood cholesterol level

Ways to control cholesterol levels for people who have a high blood cholesterol level fall roughly into these categories:
- a low cholesterol, low saturated fat diet
- avoiding excess alcohol
- losing excess weight
- physical exercise (which influences how your body handles cholesterol).

See our topic on high blood cholesterol

For some people, these steps may not be enough (remember, your body is producing cholesterol all of the time) and your doctor may recommend additional help to lower your cholesterol level by prescribing:
- drugs that inhibit the body's own cholesterol production (statins)
- drugs that inhibit the absorption of cholesterol through the intestine wall (cholesterol absorption inhibitors)
- drugs (fibrates) that improve the balance of lipoproteins.

everybody Human Atlas: High Cholesterol

Original material provided by everybody. Updated December 2009.