The functions of cholesterol include:
- a component of cell membranes (as are saturated fatty acids) to aid structure and rigidity
- synthesis of hormones such as oestrogen, testosterone and cortisol
- synthesis of bile used to digest fat
- synthesis of a precursor to vitamin D when the skin is exposed to sunlight
Sources of cholesterol are meat, poultry, egg yolks, fish, seafood and dairy produce. The body is also able to synthesise cholesterol in the liver if the daily intake from our diet is inadequate.
Cholesterol and fatty acids do not mix with blood which is predominantly water based. The body has therefore developed protein based carriers called lipoproteins which transport them in the blood and deliver them to the body's tissues.
The three key lipoproteins are:
- Very low density lipoproteins (VLDL). Contain both cholesterol and triglycerides (3 fatty acids and a glycerol bond) from the liver. Function: to transport triglycerides into adipose tissue
- Low density lipoproteins (LDL). Formed once the VLDL's have unloaded the triglycerides and transports cholesterol to other cells and tissues throughout the body for repair and renewal.
- High density lipoproteins (HDL). Transport excess cholesterol from the tissues and blood back to the liver where it is recycled.
So what is meant by "good" and "bad" cholesterol?
LDL is described as bad cholesterol as high LDL levels in the blood have been linked with coronary heart disease.
Just to be clear, LDL is actually the lipoprotein containing cholesterol, it is not the cholesterol itself which is bad.
It is also important to understand that not all LDL is bad as LDL is required in the body as described above to carry cholesterol to the cells for tissue repair and renewal. What is important to know about LDL, and is not well publicised, is that there are different sized particles. If the particles are too small and dense they can block artery walls and do not flow easily around the body. They can get stuck together, begin to oxidise, cause inflammation and damage the artery walls leading to heart disease. Large LDL particles do not get stuck in this way.
So how do we ensure we have LDL particles of the correct size?
The LDL particle size is influenced by a number of factors which can be genetic, environmental or hormonal but it is also recognised that another influential factor is eating a healthy balanced diet. Research has shown that trans fatty acids (found in processed foods where vegetable oils have been hydrogenated) can adversely affect the number of small and dense LDL particles [JF Mauger et al, American Journal of Clinical Nutrition 2003, Vol.78 No.3 370-375].
Can medication help?
Modern medicine does not actually regulate the size of the LDL particles but usually focuses on the relative quantities of HDL and LDL particles. This may indeed reduce the risk of heart disease for some individuals but does not necessarily look at the cause of the problem nor avoid any side effects associated with taking this type of drug.
Sue_O'Neill
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