Hyperlipidemia or dyslipidemia is also called high blood cholesterol. Cholesterol is a waxy white fatty molecule which is an essential part of every cell membrane. It is also a building block for many important molecules such as testosterone, estrogen and other hormones, as well as bile acids, which are a vital part of many body functions. It is synthesized in the body, and also absorbed from animal foods.
Cholesterol levels correlate with the risk of developing coronary heart disease. This is because of fatty buildup, called plaque, under the inner lining, or endothelium, of the blood vessels. As the plaque grows larger, it ulcerates or cracks on the surface.
The injured endothelium now attracts platelets, and clot formation starts. This process results in partial or total blockage of flow through the vessel, causing various manifestations of vascular disease. Apart from angina and heart attacks, this includes stroke and related events.
Different types of cholesterol are classified according to their source of origin and lipoprotein content, as LDL, VLDL, IDL, HDL, and chylomicrons. One type of high cholesterol is due to a genetic defect which knocks out LDL receptors, and prevents the uptake of LDL into the cells. This is called familial hypercholesterolemia.
Familial hypercholesterolemia has the following characteristics:
- Severe elevation of LDL cholesterol above 260 mg%
- Tendon xanthomas
- Premature coronary heart disease
- Familial combined hypercholesterolemia
- Cholesterol, or LDL cholesterol, or both, in different members of a family, and is also associated with premature atherosclerosis and heart disease.
Causes of elevated LDL
- Familial – due to genetic aberration
- Secondary:
- Obesity
- Diabetes
- Renal failure
- Alcohol abuse
- Hypothyroidism
- Sedentary lifestyle
- Nephrotic syndrome
- Estrogen replacement
- Obstructive liver disease
The most common causes are alcohol overuse, diabetes and hypothyroidism.
Other risk factors
Family history of early stroke or heart disease
Complications
- Heart disease – angina and heart attack
- Stroke and transient ischemic attack
- Peripheral arterial disease
Diagnosis
A blood test called the serum lipid profile measures the different types of cholesterol in the blood. Fats in the blood are transported as lipoproteins, which are made up of lipids and proteins. The protein part is synthesized mostly in the liver, but one type is formed in the intestinal cells. The components of the lipid profile include:
Total cholesterol
The sum of various forms of cholesterol in the blood
Triglycerides
Simple fats, composed of fatty acids joined to a glycerol molecule
Very low-density cholesterol (VLDL)
Rich in triglycerides, and therefore very light, these particles carry triglycerides to the body’s cells for use or storage. An enzyme called lipoprotein lipase split triglycerides at the cell surface of the endothelial cells, to form monoglycerides and fatty acids, which can diffuse into the cell.
Low-density cholesterol (LDL)
Also called ‘bad’ cholesterol, this is rich in triglycerides and therefore low in density. This type of cholesterol is formed in the liver from VLDL after the removal of triglyceride, and is therefore a little richer in protein than VLDL. It enters cells to take part in hormone synthesis or membrane formation, and requires the LDL receptor for internalization. Excess LDL is removed from the liver for excretion as bile acid or bile salts.
High-density cholesterol (HDL)
Called ‘good’ cholesterol, the lipoprotein in this molecule is formed in the liver, and travels in the bloodstream, picking up excess cholesterol to take back to the liver, which excretes it in the form of bile. Thus a high HDL means less cholesterol in the bloodstream, and a lower risk of fatty buildup in the arteries, because it keeps LDL levels low.
The test may also measure the ratio of total cholesterol to HDL.
Treatment
Non-medical therapies include:
- Exercise
- Smoking cessation
- Dietary changes to reduce the amount of fat – low in animal fats, higher in plant foods and saltwater fish such as sardines and mackerel, and low sugar.
- Correcting secondary contributing factors, such as obesity, thyroid disease and diabetes.
Medical treatment includes drugs to reduce cholesterol levels, such as statins, niacin, fibrates, ezetimibe. Each class has different mechanisms of action, and specific uses, depending on which cholesterol fraction needs to be reduced.
References
Further Reading
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