High cholesterol levels have been a concern for people everywhere, especially in the last couple of decades. Doctors tell us that high cholesterol can lead to heart disease or stroke.

Cholesterol comes from food -- as most of us know -- but it is also formed in the body. In fact, your body makes all that it needs, so any cholesterol you ingest from food is unnecessary.

There is good cholesterol and bad cholesterol: Bad cholesterol is low-density lipoprotein -- or LDL -- cholesterol, while good cholesterol is high-density lipoprotein -- or HDL -- cholesterol. These two forms actually work against each other; one increases heart-disease risk, while the other decreases the risk.

LDL cholesterol carries the bulk of the body's cholesterol in the blood to the liver and tissues, which use it to form cell membranes. When there's an abundance of LDL, cholesterol can build up in arteries and lead to a buildup, a condition called antherosclerosis. When such a buildup forms in coronary arteries, blood flow to the heart is slowed or blocked -- causing a heart attack. Thus, a high level of LDL cholesterol increases the risk of heart disease.

HDL cholesterol carries only one-third to one-fourth of the blood cholesterol. Some experts believe that HDL is responsible for removing excess cholesterol from buildups formed by LDL cholesterol, thus reducing the risk of heart attacks.

So how much cholesterol is harmful?

The amount of cholesterol that your body can absorb varies greatly, depending on how quickly your body makes LDL cholesterol and disposes of it. Thus, the biggest determinant of your high-cholesterol risk is heredity, since your genes determine how fast LDL cholesterol is made and removed from the blood.

According to the National Heart, Lung and Blood Institute, other ways to know if you're at risk of high cholesterol include:

• The food you eat. Two main nutrients in the foods you eat make your LDL cholesterol level go up: saturated fat, a type of fat found mostly in foods that come from animals; and cholesterol, which comes only from animal products.
• Weight. Excess weight tends to increase your LDL cholesterol level.
• Physical activity. Regular physical activity may lower LDL cholesterol and raise HDL cholesterol levels.
• Age and sex. Before menopause, women usually have total cholesterol levels that are lower than those of men the same age. After age 50, however, women's total cholesterol levels are higher than those of men of the same age. As women and men get older, their blood cholesterol levels rise until about 60 to 65 years of age.
• Alcohol. Alcohol intake increases HDL cholesterol but does not lower LDL cholesterol. However, too much alcohol can damage the liver and heart muscle, and lead to high blood pressure.
• Stress. Stress over the long term has been shown in several studies to raise blood cholesterol levels.

Sources:

• National Heart, Lung and Blood Institute
• Columbia University's Health Education Program