What Is Cholesterol?
Cholesterol may already be familiar to you as a risk factor for coronary-artery disease. But cholesterol is also vital to good health. Cholesterol is a type of a lipid, a soft, fat like substance that serves as a source of fuel and contributes to cell structure, the manufacturing of hormones and other biological functions. Cholesterol is manufactured by the liver. (In fact, your body manufactures all the cholesterol you need from other fats in your diet; you don't need to consume any cholesterol to maintain health.) You can also get cholesterol from consuming animal foods, such as meat, eggs and dairy products.
Although cholesterol is vital to a variety of life-sustaining functions, too much cholesterol in your blood is a major risk factor for heart disease. Excessive cholesterol can cause buildup of atherosclerotic plaque. Accumulation of plaque in arteries can block blood flow and lead to a heart attack.
What Causes Excessive Cholesterol?
To understand how excessive cholesterol occurs, consider how cholesterol travels in your body. Cholesterol doesn't dissolve in water. Therefore, to circulate through your blood (which is mostly made up of water), cholesterol and triglycerides (another lipid in the blood) combine with proteins to form lipoproteins.
There are four types of lipoproteins, each differing in the ratio of cholesterol and triglycerides to protein. The main types are low-density lipoprotein (LDL) and high-density lipoprotein (HDL).
LDL cholesterol, the so-called "bad" cholesterol, is transported to sites throughout the body where it's used to repair cell membranes or make hormones. LDL cholesterol can accumulate in the walls of your arteries, just as hard water promotes a buildup of lime inside the plumbing of your house. Cholesterol deposits, however, are spotty, rather than evenly coated, throughout the arteries.
HDL, the so-called "good" cholesterol, is transported to the liver, where it's altered and removed from the body. In a sense, HDL is the clean-up crew that sops up excess cholesterol from the tissues and disposes of it before it can do any damage. In fact, there is no good cholesterol. It is the lipoprotein HDL that is "good," not the cholesterol it carries. But laboratories measure HDL cholesterol rather than HDL itself.
Using Cholesterol to Measure Heart Disease Risk
No single cholesterol or ratio of cholesterol numbers provides an absolute standard for measuring heart-disease risk. Your lipid profile includes the following measurements: total cholesterol, LDL cholesterol, HDL cholesterol and triglycerides.
Total cholesterol, LDL cholesterol, and HDL cholesterol reflect a dynamic process — cholesterol is deposited in the walls of blood vessels and then taken away. The total cholesterol level is the crudest look at this process; the LDL and HDL numbers give a more detailed look at the two-way traffic inside your blood vessels. Ideally, LDL cholesterol levels should be less than 100 milligrams per deciliter (mg/dL). An HDL cholesterol level under 40 mg/dL is low; a level of 60 mg/dL or above is excellent.
Like cholesterol, triglycerides are lipids that circulate in your blood. Triglycerides are used by the body to transport and store fat. The relationship between high triglyceride levels and heart disease is complex; clearly, however, high triglyceride levels aren't good for health. High triglyceride levels accompanied by low HDL levels appear to be especially worrisome.
Cholesterol and Triglyceride Levels
Here is information for interpreting cholesterol and triglyceride levels, based on guidelines recently issued by the National Cholesterol Education Program Expert Panel.
For people diagnosed with coronary artery disease, the optimal level of LDL cholesterol is less than 70 mg/dL.
Factors That Affect Cholesterol Levels
Factors that affect cholesterol levels include diet, exercise and genetics.
Significantly large amounts of saturated fat and trans fat in your diet can increase your cholesterol levels, more so than anything else you eat. Saturated fat is found in animal foods such as meat, fish, poultry and whole-milk dairy products, such as cream, milk, ice cream and cheese. Saturated fat is also found in butter, lard and coconut, palm kernel and palm oils. Your body easily turns saturated fat into cholesterol, which ends up in the walls of your arteries.
Trans fats are fats that start out as liquid vegetable oils, and then are transformed by a chemical process (hydrogenation) into solids at room temperature. This process turns healthy vegetable oils into unhealthy fats that raise LDL cholesterol and lower HDL cholesterol.
If you are trying to modify your diet to improve your lipid profile, focus on reducing the amount of saturated fat and trans fat in your diet rather than the absolute amount of cholesterol.
Regular aerobic exercise reduces your blood levels of triglycerides and increases your levels of beneficial HDL cholesterol.
Your genes can affect your cholesterol levels. Because of abnormal genes inherited from their parents, some people lack certain cell receptors that are needed for removing LDL from the blood. In this condition, called familial hypercholesterolemia, people can have extremely high levels of LDL cholesterol. This results from inheriting one bad gene (these people are called heterozygotes) or two bad genes (called homozygotes). Heterozygotes can develop premature coronary-artery disease, usually in their 40s to 60s, whereas homozygotes can die of heart attacks in their teens or 20s. There are also milder forms of hypercholesterolemia, which generally produce moderate elevations of cholesterol and proportionally increased risk of premature heart attacks.
Medications to Lower Cholesterol Levels
Reducing your cholesterol and other levels of blood fats should begin with lifestyle changes, such as following a low-fat diet and controlling weight, but a number of drugs can lower total cholesterol, LDL and triglyceride levels, while increasing beneficial HDL levels. If your cholesterol levels are high despite dietary changes, talk to your doctor about how to reduce them with these lipid-lowering medications:
Drug Category: Statins
How They Work: Statins block the production of cholesterol.
Some Common Agents: Lovastatin, pravastatin, simvastatin, fluvastatin, atorvastatin, rosuvastatin
Drug Category: Niacin
How They Work: Niacin reduces the liver's ability to produce very low-density lipoprotein, the precursor of LDL.
Some Common Agents: Nicotinic acid, niacin extended-release (Niaspan), niacin (Slo-Niacin)
Drug Category: Fibrates
How They Work: Fibrates activate an enzyme that speeds the breakdown of triglycerides in the blood.
Some Common Agents: Clofibrate (Atromid), gemfibrozil (Lopid), fenofibrate (Tricor)
Drug Category: Bile acid sequestrants
How They Work: These drugs bind with bile acids (which are made from cholesterol) in the intestines and remove them in the stool. More cholesterol is then used by the liver to make bile acids.
Some Common Agents: Cholestyramine, colestipol
Drug Category: Cholesterol absorption blockers
How They Work: They decrease total serum and LDL cholesterol levels by inhibiting absorption of cholesterol from the intestinal tract.
Some Common Agents: Ezetimibe (Zetia) is currently the only one approved from this category.