Two types of lipoproteins and their quantity in the blood are main factors in heart disease risk:

• Low-density lipoprotein (LDL) -- This "bad" cholesterol is the form in which cholesterol is carried into the blood and is the main cause of harmful fatty buildup in arteries. The higher the LDL cholesterol level in the blood, the greater the heart disease risk.
• High-density lipoprotein (HDL) -- This "good" cholesterol carries blood cholesterol back to the liver, where it can be eliminated. HDL helps prevent a cholesterol buildup in blood vessels. Low HDL levels increase heart disease risk.

One of the primary ways LDL cholesterol levels can become too high in blood is through eating too much of two nutrients: saturated fat, which is found mostly in animal products, and cholesterol, found only in animal products. Saturated fat raises LDL levels more than anything else in the diet.

Several other factors also affect blood cholesterol levels:

• Heredity -- High cholesterol often runs in families. Even though specific genetic causes have been identified in only a minority of cases, genes still play a role in influencing blood cholesterol levels.
• Weight -- Excess weight tends to increase blood cholesterol levels. Losing weight may help lower levels.
• Exercise -- Regular physical activity may not only lower LDL cholesterol, but it may increase levels of desirable HDL.
• Age and gender -- Before menopause, women tend to have total cholesterol levels lower than men at the same age. Cholesterol levels naturally rise as men and women age. Menopause is often associated with increases in LDL cholesterol in women.
• Stress -- Studies have not shown stress to be directly linked to cholesterol levels. But experts say that because people sometimes eat fatty foods to console themselves when under stress, this can cause higher blood cholesterol.

Though high total and LDL cholesterol levels, along with low HDL cholesterol, can increase heart disease risk, they are among several other risk factors. These include cigarette smoking, high blood pressure, diabetes, obesity, and physical inactivity. If any of these is present in addition to high blood cholesterol, the risk of heart disease is even greater.

The good news is that all these can be brought under control either by changes in lifestyle -- such as diet, losing weight, or an exercise program -- or quitting a tobacco habit. Drugs also may be necessary in some people. Sometimes one change can help bring several risk factors under control. For example, weight loss can reduce blood cholesterol levels, help control diabetes, and lower high blood pressure.

But some risk factors cannot be controlled. These include age (45 years or older for men and 55 years or older for women) and family history of early heart disease (father or brother stricken before age 55; mother or sister stricken before age 65).