Laura Andersson, a visiting professor of chemistry at Vassar College in Poughkeepsie, N.Y., answered as follows:

What people refer to as good cholesterol and bad cholesterol are not really cholesterol at all. They are actually carrier proteins that act like "baskets" to transport cholesterol between the blood and the liver. The "bad" form is low-density lipoprotein, which carries cholesterol from the liver, where it is made, to the blood. It is considered bad because too much cholesterol in the blood slowly clogs arteries, eventually causing heart disease. On the other hand, what is termed "good" cholesterol is a high-density lipoprotein that transports cholesterol from the blood to the liver.

Your body makes cholesterol because it is a building block for a number of essential substances. These include:

  • Pre-vitamin D, which is converted by sunlight to vitamin D
  • Testosterone, the "male" sex hormone
  • Estrogen, the "female" sex hormone
  • Progesterone, a sex hormone found in both males and females
  • Bile salts, that nasty yellow stuff that comes up with severe nausea
  • Other critical steroid hormones that help to regulate such important things as potassium and sodium levels
  • Excess cholesterol is "stored" in the blood. The actual cholesterol levels are determined by a number of factors, including heredity, diet and exercise. Diet appears to be the most important of these.