Despite all the bad press it receives cholesterol is not some sort of poison. It is an essential component of all body cells and of many important circulating chemicals in the blood.
The concentration of cholesterol in the blood matters because the higher it is, the more it is deposited as waxy plaques on the walls of the arteries, the coronary arteries supplying blood to the heart, the brain arteries, the aorta and leg arteries. The plaque causes the arteries to narrow, which means dangerous blood clots are more likely to form, and all of this can lead to partial or complete destruction of the organs supplied by these arteries.
Many scientific studies in many countries over many years have confirmed a close connection between the average levels of blood cholesterol in large groups of people and their chances of developing coronary heart disease under the age of 65, and a similar but somewhat less close connection for individuals. There is no doubt whatever that in all societies where average blood cholesterol is low coronary heart disease is rare, or that in all societies where average blood cholesterol is high coronary heart disease is very common. This remains true even if other risk factors for coronary heart disease are common in the low-cholesterol societies. For example, although high blood pressure and heavy smoking are extremely common in China (resulting in high number of strokes) coronary heart disease remains rare, whereas in Western countries (such as Sweden), where both smoking and controlled high blood pressure have become much less common, the average blood cholesterol has not fallen, and coronary heart disease remains common.
When it comes to individuals, there is consistent evidence that your personal level of blood cholesterol is linked to and mirrors your personal risk for coronary heart disease (although very inaccurately if considered in isolation from other major risk factors such as smoking, blood pressures and your family history). There is also some evidence that if people at very high risk of coronary heart disease (i.e., with a greater than 3% risk of a fatal heart attack during the next 12 months) reduce their blood cholesterol by reducing their fat intake and (or taking cholesterol lowering medication), about 17 fatal heart attacks can be prevented per 1,000 people treated over one year. People at medium risk have not been shown to benefit from such treatment, and those at low risk can be expected to have a bit more than one additional death per 1,000 treated over one year. These extra deaths seems to occur only in people on medication, not those treated by diet alone.
There are still a few doctors who refuse to believe there is any connection between blood cholesterol and coronary heart disease, just as there are still one or two who deny any casual link between smoking and lung cancer.
Source of Cholesterol in the Blood
Cholesterol itself can be found in food (it is present in large quantities in some foods such as egg yolks, liver, kidneys, fish) but most of it is formed in your body from the many different sorts of fats and oils found in what you eat. It is then distributed where it is needed in the body. If there is a surplus, most of this is stored in the liver, but remains circulating in the blood.
Good and Bad Cholesterols
Indeed there are good and bad cholesterols. When doctors talk about “blood cholesterol” they normally mean total cholesterol, but this is actually made up of three different cholesterol¬ containing substances.
If 10 ml of blood is left standing in a glass tube until it has clotted, the cholesterol it contains becomes easily visible as a cloudy yellowish substance, occupying the top quarter or so of the tube. It looks like what it is, a sort of fat. If this is put in a high speed centrifuge the yellow foodstuff separates into three fractions. These are High Density Lipoprotein (HDL), Low Density Lipoprotein (LDL) and Very Low Density Lipoprotein (VLDL) cholesterol.
LDL and VLDL cholesterol are ‘bad’ cholesterol, the source of waxy plaques on the walls of the aorta, coronary arteries, brain arteries and leg arteries that ultimately weaken or block. These vessels can cause organ damage by clotting or bleeding. HDL cholesterol, on the other hand, is ‘good’. Many studies have shown that concentrations of HDL cholesterol above 1.5 mml make coronary heart disease less likely, and low levels (below 1 mm) make it more likely. This is probably because HDL is the form in which cholesterol is transported in the blood before storage in the liver or excretion in bile. LDL and VLDL are thus measures of a tendency to deposit harmful cholesterol in artery walls, whereas HDL is a measure of beneficial transport of cholesterol to the liver or to be excreted in bile.
Blood Cholesterol Measurement: Normal Levels
From the sample of blood either from a finger prick, or ear lobe prick sample using a desk top machine, or from a sample taken from a vein sent to a hospital laboratory, blood cholesterol concentration is measured in millimoles per litre (abbreviated to mmol). The normal value varies between countries (mainly because of differences in fat intake) from an average below 4 mmol in China to nearly 6/mmol in the UK. For individuals, blood cholesterol levels can vary from about 3.5 mmol to about 15 mmol, and they can also vary from hour to hour and day to day. Levels under 5.2 mmol are usually regarded as desirable and over about 6 mmol are usually regarded as being high.
As LDL and VLDL together usually account for about 80 percent of the total blood cholesterol, the total blood cholesterol can generally be accepted as a valid though approximate measure of ‘bad’ cholesterol, while ignoring the contribution from ‘good’ cholesterol.
Sophisticated measurements of blood fats (lipids) often also include, triglyceride, the form in which fat is first absorbed from the gut. Measurement of triglyceride is rarely of practical value except in diabetes and in a special case called inherited familial type cholesterol aemia. High values are commonly associated with being fat or with high alcohol consumption, or both, once these are taken into account. High triglyceride is a poor independent predictor of the risk of coronary heart disease.
Measurements of cholesterol fractions and triglyceride are obviously more complex and costly for the laboratory, but they are also more bothersome for the person being tested while total cholesterol and HDL cholesterol can be measured accurately on any blood sample. LDL and VLD cholesterol and triglyceride can only be measured accurately after a minimum fasting period of 12 hours, during which no food or drinks other than water can be taken.
Screening for blood cholesterol level in isolation from other risks for coronary heart disease (or screening for multiple risks where the results are not brought together and intelligently interpreted for each individual case) can result in much higher risk than they actually are. In consequence, they may be frightened into accepting the treatment on extremely doubtful evidence.
Blood cholesterol levels should be measured routinely only in people with other risk factors for coronary heart disease ¬people with blood pressure high enough to consider treatment, people with diabetes or glucose intolerance, people who continue to smoke, and people with a family history of coronary heart disease affecting a parent, brother or sister before they reach 60 years of age.
High blood cholesterol to a large extent is inherited. Regardless of inheritance people on an extremely low fat diet cannot have high blood cholesterol level. But once people are rich enough to eat as much as they want of the cheaper food available, then what mainly determines individual blood cholesterol level is not what you eat but your personal chemistry, and this is strongly inherited. A very few people (fewer than one in every 500) have inherited genes for very high blood cholesterol, a condition called inherited familial Hypercholesterol Anemia. These people have total blood cholesterol levels around 9-15 mmol with very high LDL and VLDL (bad) cholesterol levels, very low HDL (good) cholesterol levels, and usually very high triglyceride levels.
HDL can be substantially increased by exercise, by stopping smoking and by drinking alcohol in moderation, changing one’s diet to low fat foods and changing your lifestyle to make it more exercise friendly, stress free and relaxed.