Cholesterol

Cholesterol is a lipid (a fat-like substance) that occurs naturally in the body. It's essential to help you function properly, but your body generally makes all it needs.

Cholesterol is transported in the blood by carriers called lipoproteins. There are two main types: low-density lipoprotein (LDL) is usually referred to as "bad" cholesterol because it can clog up your arteries; high-density lipoprotein (HDL) is known as "good" cholesterol because it helps take cholesterol out of the bloodstream.

Triglycerides form much of the fat stored by our body. High triglyceride levels have been linked to many diseases including heart disease and stroke.

High cholesterol doesn't produce any symptoms and many people first learn they have it only when they have a heart attack or stroke. Certain lipid rates are also risk factors for other conditions (see "Blood glucose"), so it's useful to know your numbers.

You'll usually be asked not to eat for 9 to 12 hours before your test - so that your food has had time to be digested and won't affect the results. The lipid profile from a blood test after fasting gives a breakdown of total cholesterol, LDL, HDL and triglycerides, and the ratio which is used to check your risk. A finger-prick cholesterol test (such as what's offered by some pharmacies) gives you total cholesterol only.

Risk factors

Eating too much saturated fat leads to excessive cholesterol in your blood, which can increase your risk of heart disease and stroke. Being overweight and excessive alcohol drinking are also risk factors.

The numbers:

Aim for:

• Total cholesterol (TC) below 4 mmol/L
• LDL below 2.0 mmol/L
• HDL above 1 mmol/L
• TC/HDL ratio below 4.0
• Triglycerides below 1.7 mmol/L.

Any lowering of total and LDL levels and any raising of HDL cholesterol can be beneficial even if you're not reaching the targets.

• Check it: Every 5 years from age 45 for men, 55 for women (but from 10 years younger if you're in a high-risk group). It requires a blood test.

Jargon buster

mmol/L: millimoles per litre - a measure of concentration using molecular count.