This is an abbreviated version of the complete article.*
Basic Facts
Physicians use the term lipid disorders to describe several conditions in which high concentrations of lipids (fats) exist in the bloodstream.
Lipid disorders can be caused by genetics, lifestyle, or a combination of both.
Atherosclerosis, which is the buildup of fat and cholesterol-laden plaque in the walls of the heart's arteries, can result from lipid disorders.
Lifestyle changes are important for treating lipid disorders. If the cause is genetic, or if lifestyle changes do not improve the levels of fat in the bloodstream adequately, then the physician will prescribe medications.
Lipid is the scientific term for fats in the blood, and the term is used to describe fatty acids, neutral fats, waxes, and steroids. The two main types of lipids that affect heart disease are fatty acids and cholesterol. When three fatty acid molecules combine with glycerol, they form triglycerides; when they combine with cholesterol, they form cholesterol-esters; and combining with phosphorus makes phospholipids.
As people age, their coronary arteries can develop atherosclerosis, or hardening of the arteries, the buildup of fatty streaks and cholesterol-laden plaque in the artery walls. Coronary heart disease, or CHD, is diagnosed when the accumulation of plaque in a coronary artery grows large enough to obstruct blood flow to the heart.
Lipids do not dissolve in water. For cholesterol and fatty acids to be carried in the blood and used in cells, the body must use a kind of protein called apoproteins to transport the lipids through the blood and into the cells. These protein-bound fats are called lipoproteins, and when physicians speak of lipid disorders, they generally refer to problems with the amounts of these lipoproteins in the blood.
Each lipoprotein contains cholesterol, cholesterol-esters, triglycerides, phospholipids, vitamins, and apoproteins. Lipoproteins are grouped into different classes based on their density, or how tightly packed together these different substances are. The lipoprotein classes include:
High density lipoproteins (HDL): Called the good cholesterol, HDL picks up excess cholesterol in the blood and the body and carries it back to the liver, where it is broken down and removed from the body.
Low density lipoproteins (LDL): Called the bad cholesterol, LDL carries cholesterol and deposits it in body tissues to be used for cell repair or for energy high levels of LDL.
Very low density lipoproteins (VLDL): Made up mostly of a core of triglycerides, with small amounts of proteins and cholesterol, VLDL particles circulate in the blood, the triglycerides are absorbed by cells for energy, leaving the protein and cholesterol remnants.
Lipid disorders include:
Primary elevated cholesterol (LDL levels of more than 130 milligrams per deciliter, or mg/dL);
Dyslipidemic syndrome (also called Syndrome X, a group of metabolic risk factors that significantly increases the risk of developing CHD);
Primary elevated triglycerides (triglyceride level as high as 1,500 mg/dL);
Primary low-HDL syndromes (also called dyslipidemia or dyslipoproteinemia), in which HDL is less than 35 mg/dL;
Hyperlipidemia, or high cholesterol;
Familial hypercholesterolemia, (a genetic disorder that increases total and LDL cholesterol); and
Familial hypertriglyceridemia, inherited high triglycerides.
CAUSES AND RISK FACTORS
Genetics and lifestyle can affect blood lipid levels. Some people suffer from lipid disorders that are a combination of genetic problems and lifestyle factors.
Lifestyle factors that can raise the cholesterol level include a diet high in fat and cholesterol-laden foods, and not exercising, which can lower the level of HDL in the blood.
Some people have lipid disorders caused by another disease or medical condition, called secondary lipid disorders, including:
Diabetes mellitus;
Hypothyroidism;
Obstructive liver disease; and
Kidney failure.
Lipid disorders can also be caused by steroid use.
DIAGNOSIS
To diagnose a lipid disorder, a physician tests the amount of lipids in a person's blood and compares the results to established ranges, which show whether a person's lipid level is abnormal enough to warrant treatment.
TREATMENT APPROACH
For people at high risk of heart disease or for people who have already developed coronary heart disease, typical target lipid levels are:
Total cholesterol of less than 200 mg/dL;
Total triglycerides of less than 150 mg/dL;
LDL of less than 100 mg/dL; and
HDL of 40 mg/dL or more.
To reach these goals, physicians first recommend lifestyle modification, such as reducing dietary saturated fat and losing weight.
If lifestyle changes do not lower lipid levels sufficiently, physicians can prescribe lipid-lowering medications, including:
Statins;
Bile acid sequestrants;
Fibrates; and
Niacin (Vitamin B3).
People with diabetes should avoid niacin.
Medical Review Date: March 13, 2008
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