Cholesterol
Cholesterol is a fatty substance found in all cell membranes. The nervous system contains about 40% of all the body cholesterol. Cholesterol comes in two parts "Chole" = bile and "Sterol" = steroid.
Required by the body for a number of health reasons, unfortunately it has always been given a bad name. The main functions of cholesterol are:
- Maintaining the health and integrity of all cell membranes.
- Involved in the synthesis of hormones - testosterone, estrogens, progesterone, cortisol.
- Synthesis of bile salts, and activates the synthesis of vitamin D.
- Helps the kidneys regulate the body's blood / water balance.
An excess of cholesterol in the bile can lead to gallstones, and excess in the blood can become deposited on the artery walls leading to Coronary Heart Disease.
There are four main types of lipoproteins all having slightly different structures and functions.
(a) Chylomicroms: Rich particles formed in the intestine from dietary fats, they aid in transporting dietary triglycerides to the bodies fat cells, and also transport dietary cholesterol to the liver.
(b) VLDL (Very low density lipoproteins) - Synthesized by the liver, containing triglycerides and cholesterol. They travel around the blood stream and cells, removing triglycerides, the VLDL remove cholesterol from lipoproteins in the blood stream to become low-density lipoproteins.
(c) LDL (Low density lipoprotein) 20 % protein shell and 80 % triglyderides. They transport the cholesterol from the liver to the tissues. Here it is broken down less easily than the VLDL's and used for cell membrane metabolism and hormone production etc. Excess levels contribute to the formation of atheroma, increasing the risk of CHD, coronary heart disease.
(d) HDL (High density lipoprotein) : High levels are not associated with atheroma or CHD. HDL's, act as scavengers by removing cholesterol from the blood before it can enter the arterial wall, and returning it to the liver.
Dietary cholesterol only comes from food of animal origin (foods high in dietary cholesterol are egg yolk, cream, full fat milk, cheddar cheese, liver, kidneys and prawns).
However most of the cholesterol in the body does not come from the diet, it is manufactured by the body the liver, between 800mg - 1,500mg per day, because it is an essential component of every cell membrane.
It is also needed for the synthesis of bile acids and a number of hormones, including the steroid sex hormones and Vitamin D.
The following factors all show an effect on cholesterol in the body.
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When looking at cholesterol levels, you should aim to have good levels of HDL's, compared to LDL / VLDL.
High cholesterol levels are not always unhealthy for you, it is the ratio that you have, simply put HDL's are good as they transport the LDL's (bad) lipoproteins back to your liver where they can do less harm to your artery walls.
Cholesterol is measured in millimoles per liter of plasma, expressed as (mmols/l).
| < 5 mmols | Reduced risk of CHD |
| 5.2 mmols | Suitable upper level |
| 5.3 - 7.5 mmols | 5 x risk of CHD in males |
| 7.6 - 14 mmols | 10 x risk of CHD in males (Hypercholesterolaemia) |