The American Heart Association defines cholesterol as a "soft, fat-like, waxy substance found in the bloodstream and in all your body's cells." More specifically, cholesterol is a sterol and a lipid, meaning that it is a relatively solid substance. About seventy-five percent of the body's cholesterol is manufactured in the liver and a mere twenty-five percent is absorbed from external sources. Cholesterol is necessary for important bodily processes such as the production of cell membranes and bile acids and the manufacture of Vitamin D and certain hormones such as progesterone, testosterone, estradiol, and cortisol. The body also uses cholesterol for the insulation of nerves. Everyone's body contains cholesterol. Cholesterol is also found in plants, but plants don't suffer from high cholesterol. What is it that makes cholesterol dangerous in humans?

The human body generally manufactures all of the cholesterol it needs to perform necessary functions. Therefore, cholesterol absorbed from dietary sources, the foods we eat, is unnecessary to the body's functioning and may, in fact, cause serious health problems. However, it is not the presence of cholesterol in the body that is cause for alarm, but the presence of cholesterol in the body's blood vessels, specifically the arteries, that can be the cause of such problems as heart disease and stroke.

Dietary cholesterol is absorbed from many different foods. Fruits and vegetables, and other plant foods, do not add a significant amount of cholesterol to the human diet. However, to say that humans get absolutely no cholesterol from plant sources may be a dangerous statement. Modern nutritional thought indicates that, while the amount of cholesterol absorbed from plant sources may be minimal, cholesterol levels are cumulative and therefore the amount of cholesterol from plant sources may need to be considered. Most dietary cholesterol comes from the animal products that are consumed. Foods such as meat, milk, butter, cheese, eggs, poultry and fish are examples of cholesterol-containing foods. Additionally, foods such as cookies and French fries, may contain trans fats even though they are not animal products. Some trans fats are found naturally in animal products, but most are actually man made and are used in the manufacture of snack foods, fried foods, baked goods and fast foods.

Good cholesterol, or high-density lipoproteins (HDL), is responsible for carrying cholesterol from the bloodstream to the liver for elimination. Bad cholesterol, or low-density lipoproteins (LDL), carries cholesterol from the liver to the bloodstream and is responsible for the buildup of cholesterol in the arteries. To maintain a healthy balance, the body must have more HDL than it does LDL.

It is important to understand what types of fats have what type of effects on cholesterol. The following chart, provided by the Harvard School of Public health, lists several different types of fats and what effect they may have on the body's cholesterol levels.

Generally, liquid fats are known to have a less detrimental effect on the body's cholesterol levels. Also generally, the more solid the fat, the more it raises LDL, or "bad" cholesterol.

Normal cholesterol levels vary and it is important to note that high cholesterol levels are not solely determined by diet. It is possible for an individual who subscribes to a healthy diet and exercise program to have dangerous levels of LDL cholesterol and it is possible for an individual who consumes high levels of saturated fats to have low levels of LDL cholesterol. The new cholesterol-lowering drug, Vytorin, claims to combat the two sources of cholesterol - "the foods you eat, and your family history."

The American Heart Association lists a "desirable" total blood cholesterol level as being less than 200 mg/dl. An individual who has a total blood cholesterol level of between 200-239 mg/dl, is at borderline high risk. And any individual with a total blood cholesterol level of more than 240 mg/dl is at high risk for a heart attack or stroke. Low-density lipoprotein levels should be less than 100 mg/dl. Any LDL level that is over 130 is cause for concern and an LDL level that is more than 190 indicates a high-risk individual.

Medical professionals know that cholesterol, in and of itself, is not bad. The body needs cholesterol to survive. It is the overabundance of cholesterol, causing a buildup of unused and unnecessary fat in the arteries that can lead to serious health concerns. Cholesterol that has built up in the bloodstream is called plaque. Over time, plaque can block an artery either partially or completely much like a sink drainpipe becomes clogged. This buildup of plaque is called atherosclerosis. If an artery becomes blocked, blood cannot flow properly to the body's heart, muscles, and brain.

As plaque builds up in an artery, the blood to the organ(s) supplied by that artery becomes diminished. The heart is supplied by the coronary artery. As the coronary artery becomes clogged, blood flow is restricted and less oxygen reaches the heart. An individual whose heart muscle is starved for oxygen may experience angina (chest pain) and even tissue damage or death. A complete blockage of the coronary artery may lead to a heart attack. An individual who is suffering from a blockage of an artery that leads to the brain may experience a stroke.

At one time, medical professionals believed that it was primarily men who suffered from the adverse effects of high cholesterol. Modern medical thought however, recognizes the effects that high levels of cholesterol have had on women.