DEAR DR. DONOHUE: What causes the stomach to lose its intrinsic factor? My husband developed pernicious anemia and was told it came from loss of intrinsic factor. Any light you can shed on this would be appreciated. – J.M.

ANSWER: Vitamin B-12, found only in meat and dairy products, has many important functions. One is keeping the cells lining the digestive tract healthy. One sign of a B-12 deficiency is a beefy-red, sore tongue, an indication that the digestive tract lining is deteriorating. A second B-12 role is preserving the insulating material around nerves and around nerve cells in the spinal cord. Without that insulation, nerve transmission falters. People complain of numbness or unpleasant, even painful sensation. They wobble because balance is affected. Thinking often becomes foggy.

The third and perhaps most important B-12 function is maintaining the production of red blood cells. B-12 lack leads to a severe anemia with all its signs and symptoms – tiredness, weakness, shortness of breath. This is pernicious anemia, and often the digestive tract problems and nerve disturbances accompany the drop in red blood cell numbers.

The absorption of B-12 from the digestive tract into the blood is unique among vitamins. B-12 requires intrinsic factor, a protein produced by stomach cells, to pass through the digestive tract lining and reach the circulation. Elderly people experience a drop-off in intrinsic factor as a consequence of aging. More troublesome, however, is an attack by the immune system on the stomach cells producing intrinsic factor. Evidence of the immune attack is found in antibodies directed against those stomach cells. Antibodies are the immune system’s ammunition.

One bright spot to the pernicious anemia story is that restoration of body B-12 stores can be obtained by injecting the vitamin into muscles. Injections bypass the need for intrinsic factor, and results are usually gratifying.

DEAR DR. DONOHUE: I would like to know how long the cold germ lives after leaving an infected person’s body. For example, if a person coughs into his hands and then touches a doorknob, how long does the germ live on the doorknob? – J.B.

ANSWER: More than one virus can cause a cold, but the chief troublemaker is the rhinovirus, so I’ll use it as the model.

Rhinoviruses can live on inanimate surfaces, like doorknobs, for several hours. However, touching a doorknob coated with rhinovirus seldom, if ever, is the way colds are passed from one person to the next.

Hand transmission accounts for most passage of colds. People who are infected with the rhinovirus invariably have some virus on their fingers and hands. When an infected person’s hand touches another person’s hand, the second person acquires the virus. Then that person inadvertently touches the nose or the eye, and the virus penetrates the nasal lining or the eye covering and establishes a new home for itself. A cold is born. This is the reason why hand-washing is such an important preventive measure in controlling the spread of colds.

Rhinoviruses can also be sprayed into the air from a cough or a sneeze – another route of transmission, but not as important as the hand route.

DEAR DR. DONOHUE: I have just tested positive for the AIDS virus. I feel quite well, but I have asked my doctor to begin treatment. He says it’s not done that way. Why not? Why should I wait until I become sick to take medicine? Wouldn’t early treatment stop me from becoming sick? – R.S.

ANSWER: There is no convincing data that supports early treatment. And treatment is not withheld until a person becomes sick. It’s started when there is a drop in the CD4 lymphocyte count. CD4 lymphocytes are one kind of white blood cell, the ones attacked by the AIDS virus.

Well after their numbers drop, a person becomes ill. Another indication for treatment is a high blood level of the AIDS virus.

Treatment is delayed because the AIDS medicines can have serious side effects.

All of this is subject to change if evidence is ever obtained that treatment is beneficial when the AIDS test first turns positive.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from www.rbmamall.com.