health and disease
PRACTICE of medicine has changed. Instead of coming with a complaint of physical nature, patients often come with a laboratory report. One such report commonly seen is of high blood cholesterol. The patient wonders whether this is a sign of heart disease or any other complication related to this abnormality.
Our diet consists of three basic constituents ó carbohydrates (sugars), proteins and fats or lipids. The basic unit of fat is fatty acids which are long chained hydrocarbon organic acids. When three fatty acids combine with one molecule of glycerol, they form triglyceride, which is a major component of fat which we take and is stored in the body. Another component of fat is phospholipid which contain radicals of phosphoric acid along with fatty acids and is more often used in the cell structure, particularly the nervous system. Free fatty acids circulate in the blood, are the main source of energy and are in constant equilibrium with the stored fats. Cholesterol is a form of sterol and not strictly a fat, but its properties are similar to those of fats and is intimately related to the transport and metabolism of the fat and is, therefore, often taken as a kind of fat. Cholesterol is transported in the blood from the liver to the tissues and back in the form of molecules known as lipoproteins which consist of cholesterol and some specialised proteins. The formation of lipoprotein enables fats to be transported in an aqueous medium. Although it is somewhat technical, but it is extentist to briefly discuss the main varieties of lipoproteins because they are often mentioned in the Press and in public discussions, particularly in relation to heart disease. The classification and names of these lipoproteins are based on their density as is clear from the names of various fractions. In the ascending order they are - (a) chylomicrons, (b) high density lipoproteins (HDL), (c) low density lipoproteins (LDL) and very low density lipoproteins (VLDL). These fractions have different role in relation to the genesis of atherosclerosis, which is the basic disease of the blood vessels, causing heart disease, strokes and epidemic problems of other organs like kidneys, limbs and eyes, LDL is mostly responsible for causing this disease. HDL on the other hand is protective and called the good cholesterol.
Since so much stress is laid on the cholesterol level and its relation to the heart disease, one needs to know the source and disposal of cholesterol in normal and abnormal circumstances. Normally the intake of cholesterol in food is not very high. Even a rich meal usually does not contain more than half gram of cholesterol. It is desirable to limit the intake to less than 300 mgs, in a day. Common sources of this cholesterol are milk and milk products, cream, butter, egg yolk, animal sources of food, particularly mutton and sea fish. Glandular meat like liver, kidney and brain also contain a much higher amount of cholesterol.
But what is often not realised is that a much bigger source of cholesterol is the body itself. This cholesterol is known as endogenous cholesterol and is actually more than what is ingested in food. Thus the factors governing the manufacturing of cholesterol in the body, particularly in the liver, and its disposal, are very important. Intake of certain fats known as saturated fats, which are present in animal fat and oils which solidify in winter, such as coconut oil, palm oil and hydrogenated oils (Vanaspati) raise the cholesterol level. On the other hand, taking vegetable oils known as polyunsaturated fats like safflower oil, mustard oil, sunflower oil and corn oil lower the cholesterol levels. This is also done by mono-unsaturated fats like olive oil. This is the rationale behind taking less of animal fats like ghee, cream, butter, eggs, cheese etc.
Cholesterol, however, is not present in our body to create problems. Cholesterol is an integral part of all cells. It forms the membranes or the walls which hold the cells. It forms the basis of the formation of hormones like corticosteroids, and sex hormones like estrogen, progesterone and testosterone. Cholesterol after conversion into colic acid, is extremely important in the digestion of fats through bile secreted by the liver into the intestine. Its presence in the skin along with other lipids makes the skin impervious to water, otherwise one can lose a large amount of water on account of evaporation through the skin. A recent observation has been made in Chicago that cholesterol and other lipids are important in mopping up the endotoxins i.e. toxic material generated by the microbes and are therefore very important in fighting infections.
Why then we are concerned and worried about the cholesterol level all the time? A large body of epidemiological data is available all over the world which shows that there is a strong relation between cholesterol level and atherosclerosis. which is the disease of the blood vessels leading to the clogging of the channels supplying blood to vital, organs. Famous studies done in Finland, Belgium, Hungary, Sweden, the Netherlands, USA and India indicate a very close relation between high level of these lipids and atherosclerosis. In Belgium, particularly, the observation was striking. In the southern part of Belgium, where fat intake was higher, the cholesterol level and the heart disease was also higher, when persons of Japanese origin moved to the USA, they acquired higher cholesterol levels, thus increasing their heart disease. The subject is so important that National Cholesterol Education Programme are held in USA, Canada and England. European Atherosclerosis Society Guidelines are issued for the same purpose. A lot of information has been generated in India from various centres, including the PGI Chandigarh, studies conducted at Delhi and other parts of the country and Indians settled in Britain and North America. One thing which is relatively peculiar to the population of this subcontinent is that here triglycerides are often more dangerous than cholesterol. This may be based on our carbohydrate-rich diet or possibly genetic pre-disposition.
Let me briefly mention that apart from dietary factors, a large number of other pre-disposing factors can produce abnormal levels of cholesterol and predispose a person to heart disease. They include various congenital abnormalities of lipid metabolism (these people are prone to very early complications of atherosclerosis), hypothyroidism, nephrotic syndrome, diabetes mellitus, obesity, chronic renal failure and excessive alchohol intake. It will however, be too simplistic to take cholesterol as the only or main culprit in heart disease. There are numerous other factors, including high blood pressure, smoking, diabetes mellitus, obesity, lack of physical activity, mental stress, family history of heart disease and menopause in women. Many other factors are under scrutiny.
In the case of persons having high cholesterol level or high triglyceride level, the first step should be the rational treatment of the common predisposing factors mentioned above. An attempt should also be made to decrease the level without the use of drugs. Dietary modifications and other methods like exercise and charge of lifestyle should be tried for three to six months before switching over to drug therapy. The intake of cholesterol should be limited to 300 mgs and if possible to 200 mgs. Not more than 10 per cent of the calories in the diet should be contributed by saturated fats as mentioned above and more by polyunsaturated or monounsaturated fats. Regular physical exercise and a reduction of weight a long way in decreasing lipid levels. A vegetarian diet is recommended provided milk is taken without its fat content. Use of estrogen in post-menopausal women, cutting down of alcohol control of diabetes, are very helpful.
If a fair trial for three to six months of dietary therapy, exercise and other lifestyle related measures have not worked, drug therapy can be used. Fortunately, there has been a great improvement in the drugs used for this purpose and continuously better and safer drugs are being introduced (fibrates, statins, nicotinic acid, cholestyramin). Use of drugs and their rational choice should be left to the doctors, but a patient should know that these drugs take at least a few weeks to work and a fair trial is needed for at least for two to three months. It should also be known that they do not offer a permanent solution and after the level has been brought down with the drugs, maintenance should be done with the help of the diet and other changes in lifestyle. Most of these drugs work through the liver and can therefore sometime produce an imbalance in the functioning of the liver. Hence constant monitoring of the liver during therapy is requested.
Finally, let me mention that cholesterol need not create panic in patients or physicians. I have known patients who in their 70s or 80s, were denied a small amount of butter in the breakfast or an occasional egg just because their cholesterol level was 220 or 230. A balanced, rational attitude is important and other risk factors should be taken into consideration. Many laboratories these days provide information about the risk associated with a high level of cholesterol in their reports. Whereas this may be a good service, this can also generate fear and patients need to be educated about it. Remember, "What you are eating is important, but what is eating you is even more important."