nowing your blood cholesterol level is one of the keys to maintaining good health. Studies have shown that the higher your cholesterol level, the greater your risk of developing heart disease or of having a heart attack. More than half a million Americans die from heart disease every year.

When there is too much cholesterol in your blood, it builds up on the walls of your arteries. This buildup causes "hardening of the arteries" over time, narrowing the artery and decreasing or even blocking blood flow to the heart. When your heart stops receiving blood and oxygen, you experience a heart attack.

The danger is that high blood cholesterol does not reveal itself in symptoms, so people are generally unaware of their high cholesterol levels.

Knowing your cholesterol levels allows you to make changes that can lessen your risk of developing heart disease and suffering a heart attack, even if you already have heart disease. Everyone, young and old, should understand the benefits of lowering their cholesterol.

Despite the dangers of high blood cholesterol levels, it is important to understand that cholesterol is a substance that occurs naturally throughout the body and that is necessary to function normally. It is an indispensable element in cell membranes, neurons, and is used in the synthesis of hormones, including estrogen and testosterone. Cholesterol is also used in bile, which helps the body absorb fat. The body recycles much of its cholesterol, and the liver synthesizes the balance needed from the products of fat metabolism.

There are two types of cholesterol: high-density lipoproteins (HDL) or "good" cholesterol, and low-density lipoproteins (LDL) or "bad" cholesterol.

Because cholesterol, a fat, and blood do not mix, your liver packages the cholesterol it produces with protein and fatty acids in order to allow it to travel in the bloodstream more easily. If you have too much LDL in your blood, the excess will deposit on your artery walls, causing the damaging buildup that leads to heart disease and heart attack.

HDL in the blood carries cholesterol from other parts of the body back to the liver, which leads to its removal. This keeps cholesterol from building up on artery walls. The more HDL cholesterol you have in your blood, the better.

Two primary nutrients in foods will increase your LDL cholesterol level: saturated fat, found mostly in animal products, and cholesterol, found only in animal products. Eating too much of these two nutrients is the primary reason for high cholesterol levels and the high incidence of heart attacks in the US. Reducing your intake of saturated fat and cholesterol is a very important step in reducing your cholesterol level.

Blood cholesterol is influenced not only by your diet, but by how your body manages its own production and disposal of LDL cholesterol (the "bad" type). Your body produces all the cholesterol it needs, therefore you should minimize the cholesterol in your diet.

Many factors will influence your cholesterol level, including heredity, diet, weight, exercise, age, sex, alcohol consumption, and stress.

You should have your blood cholesterol level measured at least every five years. The best measure comes from a lipoprotein profile, which requires a short, 9-12 hour fast and provides information on your triglycerides, LDL, HDL and total cholesterol levels.

Even if your cholesterol levels do not demand treatment, there are several steps you can take to keep your cholesterol level low and reduce your risk of heart disease and heart attack.

• Eating a healthy diet low in cholesterol and saturated fat.
• Working regular exercise into your lifestyle.
• Maintaining a healthy weight level and avoiding smoking.
• Understanding cholesterol-lowering medicines and other treatment options.