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Cholesterol

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Cholesterol- is it important?
Dr Hew Fen Lee MBBS MD FRCP(Edin) FRACP
Consultant Endocrinologist
Subang Jaya Medical Centre

Cardiosvascular disease, which includes coronary heart disease and stroke has been the major cause of death in many countries both in the developed and the developing world. In Malaysia, this has become the biggest single cause of death. This will remain so for many years to come and ominously, there is a trend that this problem is going to increase with time. These diseases are due to a blockage of the arteries that supply oxygen and nutrients to the organs. When the artery to the heart is blocked, part of the heart muscle dies and the heart may stop working or works poorly. Similarly, if the artery to the brain is blocked, part of the brain is damaged and a stroke results. The damage to these organs is going to be permanent although some incomplete recovery may result with appropriate treatment.

Not only does cardiovascular disease cause lives, it also is a major cause of illness and disability in the community. With the advent of modern medicine, increasingly many patients are surviving heart attacks and stroke. However, many of these victims from heart attacks and stroke are left with disabilities that may leave them dependent on long term care and support from the family. The economic and social impact is immense in terms of consumption of resources and time for caregivers (family) as well as loss of income for both the patients and their family. By extension, there is going to be a need for an increase in health spending on the one hand and a loss of tax revenue for the government on the other. Thus, the impact and the consequence of the disease go far beyond individual patients as it affects the immediate family as well as the bigger community at large. It therefore makes sense to prevent the disease rather than just treating the disease when it arises.

Table 1
Common types of cardiovascular disease:
Heart attack/Heart failure
Stroke
Peripheral vascular disease causing amputation of limbs
Renal artery stenosis causing kidney failure
 

What causes cardiovascular disease?
 
There are many causes of cardiovascular disease which include genetic causes and environmental factors. The presence of family history increases the risk by 2-3 folds. The environmental factors are usually due to lifestyle factors for example smoking, diet and exercise (lack of). For most people, cardiovascular diseases are due to a mixture of both genetic and environmental factors. The presence of other diseases may also increase the risk of cardiovascular disease (please see table 2).

Table 2
Common causes of cardiovascular diseases:
Diabetes
High cholesterol levels
Cigarette smoking
Obesity
Hypertension or high blood pressure


What is cholesterol?

Cholesterol is a form of fat or lipid that is carried in the blood stream. This cholesterol is very important in the building up of new cell wall and thus is important for the regeneration of cells as well as for growth. Furthermore, there are many hormones for example, the male hormone, testosterone and female hormone, oestrogen are made from cholesterol. Thus, cholesterol is quite a useful chemical to have in the body. However, too much of a good thing is definitely not a good idea in terms of cholesterol.

There are different kinds of lipid in the blood. Not only is there cholesterol but also triglyceride which together form different kinds of cholesterol to enable the body to move these fat or lipid from one place to another for storage as well as for usage. As each of these has different structure, each also has different functions. The most well known cholesterols are the low density lipoprotein(LDL) -cholesterol and the high density lipoprotein(HDL)-cholesterol. The LDL-cholesterol is responsible for bringing fat from the liver where the fat is made and processed (metabolized) to the different part of the body either for it to be stored or for it to be used to make cells or hormones. The HDL-cholesterol on the other hand, is the one that bring the lipid back to the liver for further processing.

Where do these cholesterol come from then? We can get cholesterol directly absorbed from food particularly meat with fat. However, cholesterol is naturally made in our liver as we need the different kinds of cholesterols to do their respective jobs of transporting lipid around the body. Even if we do not eat any animal fat or even if we are vegetarians, we can still have adequate cholesterol in our body. The reason is that the liver will use the oil from food even vegetable oil to make these cholesterols. There can be a lot of fat hidden in the food while it is being prepared eg in frying.


How can high cholesterol levels affect our arteries?

The LDL-cholesterol if in a high level may end up depositing some of the lipid that they carry along the way in the arteries. With time, these arteries will become more narrow and they may be so narrow that the arteries are completely blocked- a process known as atherosclerosis. When this happens, the organ that the artery(ies) supply may die due to a lack of oxygen and nutrients that are critical for normal cells to function and survive. As a result, the cells in the organ may die for example in a heart attack or a stroke. Therefore, a high level of LDL-cholesterol will cause more of these blockages and thus speed up the process of atherosclerosis. On the other hand, since HDL-cholesterol brings back the lipid from the different parts of the body to the liver, it also mops up the lipid that has been deposited by the LDL-cholesterol thereby reducing the process of artherosclerosis. That is the reason why the LDL-cholesterol is known as the bad cholesterol and HDL-cholesterol known as the good cholesterol. Diet with high fat content increases the LDL-cholesterol levels. On the other hand, HDL-cholesterol can be increased by exercise. Some hormones may have an effect on the cholesterol levels eg thyroid hormone and the sex hormones. Similarly, other factors for example the processing of the lipid (metabolism) may be determined genetically and therefore many patients with cardiovascular diseases have a family history.


How can we treat high cholesterol levels?

As has been indicated above, lifestyle factors have a major impact on the way in which our body processes and thereby determine the levels of the cholesterols. Reducing dietary fat intake, achieving an ideal weight and regular exercise will help to improve the whole lipid profile. In some situations, other illnesses or disease(s) may be present to affect the cholesterol levels for instance diabetes, hormonal imbalance, kidney or liver diseases. Some of these illnesses may not be apparent and some of the patients suffering from it may not be aware of the conditions. Thus a medical check-up is advisable. If these measures are not adequate, then drugs can be used to reduce the levels.


Table 3
What are the optimal lipid levels?
A= Those with no history of cardiovascular diseases, diabetes or hypertension
B= Those with history of cardiovascular diseases, diabetes or hypertension

                                A           B
Total cholesterol      <6.0       <5.2
Triglyceride             <2.0       <2.0
LDL-cholesterol       <3.5        <2.6
HDL-cholesterol       >1.0       >1.0


There are many effective drugs that are available to treat lipid problems. However, there are different lipid problems and thus the drug used may be quite different from patient to patient. The common drugs are HMG coenzyme A reductase or statin (eg simvastatin, lovastatin, atovostatin); fibrate (eg gemfibrozil, fenofibrate, ciprofibrate) and nicotinic acid. Some of these drugs have side effects (eg liver irritation, muscle inflammation) but the side effects are not common and are mild; and can be easily picked up from routine assessment by the prescribing doctor. These drugs do not interfere with the hormone levels despite the reduction in cholesterol. Other supplements may help for example omega 3 fish oil but the dose needed to improve lipid levels is at least 1200mg.

What are the benefits of these cholesterol lowering medications? It has been proven that with appropriate use, the two major groups of drugs (statins and fibrates) have not only improved the cholesterol levels but also reduce the incidence and the severity of the cardiovascular diseases. There is further proof that these drugs have reduced the death rate of those suffering from cardiovascular diseases and their respective complications. Broadly, with a 1% improvement in cholesterol, there is a 2% reduction in risk. It has been shown too that the narrowing and blockage in the arteries can be actually reduced with both the statins as well as the fibrates.


Summary

Cardiovascular diseases are presently the largest single cause of death in Malaysia. Furthermore, they also bring about a reduction in quality of life and also have a major social and economical impact not only the patients but also their families and the greater community. The dictum of ‘prevention is better than cure’ is even more applicable in this situation. Given that the cause is multi-factorial, it requires a more holistic approach. Nevertheless, lifestyle factors (cessation of smoking, diet and exercise) remain the most important and effective means of improving lipid levels. However, very often, this is not adequate and thus appropriate use of medication should reduce and minimize the risk of cardiovascular diseases.

On the other hand, cholesterol is not the only factor or risk in causing cardiovascular diseases. There are other risk factors for example: diabetes, obesity, hypertension, etc. Each of these risk factors should be dealt with effectively if present. In fact one need to reduce the risk more diligently in those with multiple risk factors as their risk can be many times higher. This will ensure not only a longer life but as importantly a better quality of life.