Q: I have heard that it may be dangerous when the amount of cholesterol is too low in either the diet or the blood. Is that true?
A: No, not for normal people. In general, the lower the total blood cholesterol level, the smaller the risk of coronary artery disease. You may be referring to one particular fraction of blood cholesterol, the high density lipoprotein cholesterol, or HDL cholesterol. Because HDL protects against coronary artery disease, low levels can be dangerous.
Some years ago, several reports raised fears about the possible risks of low cholesterol levels. Subsequent studies have failed to establish any evidence that low levels of blood cholesterol cause any form of cancer.
People with several different types of rare genetic disorders produce abnormal forms of the protein component (apoprotein B) of low density lipoprotein (LDL). Such individuals not only have very low levels of blood cholesterol but may also suffer from brain dysfunction, retinal degeneration, abnormalities of their red blood cells, and an inability to absorb dietary fat.
Cholesterol also is the starting material for manufacturing the sex hormones: testosterone in the testis, estrogen and progesterone in the ovary. Advertisers for certain foods have used scare tactics by suggesting that diets low in cholesterol would reduce the body's capacity to produce these sex hormones and thereby reduce sex drive and function. In fact, the body can make enough cholesterol to maintain normal sex hormone production and sexual function even when the diet contains no cholesterol.
A physician colleague has written to request an expansion of a recent answer in a column concerning a woman who had begun to eat cornstarch. He reminded me that pica (eating substances like ice, clay or starch) may not only lead to anemia in some people but also may result from anemia. He pointed out that anyone who develops a new habit of eating cornstarch or other unusual substances may have a subtle anemia that requires medical attention from a physician.
*Dr. Margolis is professor of medicine and biological chemistry at the Johns Hopkins School of Medicine and associate dean for academic affairs at the school.