Atherosclerosis occurring in the coronary arteries is the underlying cause of coronary heart disease and hyperlipidemia is a major cause of atherosclerosis. To understand hyperlipidemia, one must understand lipid transport in the blood.
Lipids are hydrophobic molecules that are insoluble or minimally soluble, meaning that there are special requirements for transporting the lipid molecules once intestinal absorption into the plasma and into the cells throughout the body has occurred.
Lipoproteins, which are macromolecules that contain lipids and proteins known as apolipoproteins (APO) serve as vehicles for such transportation. The lipid constituents include free and esterified cholesterol, triglycerides, and phospholipids.
The four major families of lipoproteins are: chylomicrons, very-low-density lipoproteins (VLDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL).
Hyperlipidemia And Risk Factors
Hyperlipidemia (elevated levels of triglycerides or cholesterol) and reduced HDL-C levels occur as a consequence of several factors that affect the concentrations of the various plasma lipoproteins. These factors include nonmodifiable risk factors such as genetic and metabolic conditions or modifiable behaviour risk factors (eg. diet or exercise). The major modifiable risk factors include hypercholesterolaemia, hypertension and cigarette smoking.
Several epidemiological studies have demonstrated a relation between plasma LDL-C and an increased incidence of coronary heart disease, such as in The Framingham Heart Study, the Multiple Risk Factor Intervention Trial and the Lipid Research Clinics trial, all of which found a direct relationship increased between levels of LDL-C or total cholesterol and the rate of new onset coronary heart disease in men and women. In general a 10% increase in LDL-C is associated with a 20% increase in the risk of coronary heart disease.
Additionally a recent multivariate analysis of 8 year follow-up data from the large scale Prospective Cardiovascular Munster (PROCAM) Study found hypertriglyceridemia to be an independent risk factor for major coronary events, particularly in women and in individuals with type 2 diabetes.
The Hyperlipidemias (Clinical Features)
Features associated with hyperlipidemia include:
- Xanthelesmas (cholesterol deposits on the eyelid)
- Premature arcus in the cornea
- Xanthomas (cholesterol deposits in the skin)
- Rarely, lipaemia retinalis (turbid blood in retinal vessels)
Evidence of possible secondary causes should be sought.
Secondary Causes of Raised Cholesterol and Triglyceride
- Raised cholesterol
- Liver disease
- Nephrotic syndrome
- Raised Triglyceride
- Poorly controlled diabetes
- Alcohol excess
- High-carbohydrate diet
- Renal failure
- Oestrogen therapy
Initial investigation involves measurement of the fasting lipid levels (usually a 10 hour fast) including the triglyceride levels. The patient follows his normal diet the preceding 2 weeks.
General Management of Hyperlipidaemias
General principles are:
- The maintenance of a lean body weight
- A low fat and low glycaemic index diet
- Avoidance of alcohol
- Avoidance of oestrogens and thiazides
- Avoidance of smoking
- The treatment of diabetes and hypertension when present
- Moderate exercise
Modification of diet reduces cholesterol by 15-25% and triglyceride by 20-40%. Diet modification alone is therefore appropriate for those in the cholesterol range from 5.2-6.4 mmol/L.
Diet remains the basis of therapy and lipid lowering agents are an adjunct.
Advice should be geared to the individual patient than to the biochemistry report.
For example, obesity and other coronary risk factors need to be taken into account, and a more aggressive approach is called for if the patient is young, has established arterial disease or has a strong family history of this.
Lipid lowering agents
These may be effective in one of five ways:
- Reduced synthesis of VLDLs and LDLs (eg. nicotinic acid)
- Enhanced VLDL clearance (eg. bezafibrate)
- Enhanced LDL catabolism (eg. cholestyramine)
- HMG-Co-A reductase inhibition (eg.simvastatin)
- Cholesterol absorption inhibitor (eg.ezetimibe)
The drug used will depend on the side effect profile and the doctor has to decide which will be the best drug to use for that patient.
The patient must always remember that diet and exercise are still the foundation for long term overall health.
So how does all this relate to healthy aging? We know that heart disease is the number one cause of death in Malaysia and every hour one person dies of an heart attack in this country. Apart from smoking and diabetes, high cholesterol is one of the main risk factors for coronary artery disease. We cannot talk of healthy aging if we are going to have a heart attack in our thirties, forties or fifties and have premature death.
That’s why it is of paramount importance that we should have our cholesterol levels checked and if the levels are high manage it correctly, initially trying diet, exercise and nutritional supplements and if this fails than the use of pharmacological therapy is necessary especially if there are other risk factors for heart disease.
Working in partnership with a doctor who understands a holistic approach to managing high cholesterol will help and it is never too late as studies have shown that reducing cholesterol even in elderly persons in their seventies and eighties will still reduce their risk of heart disease.