DEAR DR. DONOHUE: Please explain the male hormone testosterone and all its functions. I am producing less testosterone than a woman. What could cause this low production of male hormone, and should it be corrected? – S.H.

Boys experience a surge in testosterone production at the time of puberty. Testosterone increases muscle and bone size and strength. It deepens the voice and causes the growth of facial hair. It has an important effect on the development of male genitalia. It increases sexual drive, and it also figures into the complex chain of events that produces penile erections.

Around age 50, testosterone production wanes. By age 70, its production is only 30 percent of its peak production.

Testosterone is responsible for maintaining muscle and bone strength and for all the other effects listed above. Does waning production effect undesirable changes? It might, but nature is a fairly dependable guide when it comes to the regulation of body functions.

A very low testosterone level might prompt a doctor to prescribe the hormone if a man was losing muscle size and strength and no other explanation could be found for the loss. Some doctors feel that restoring normal levels can restore a man’s potency. However, prescriptions for testosterone are not written nonchalantly. Because it lowers HDL cholesterol (good cholesterol), testosterone might promote heart attacks and strokes in older men. The hormone spawns prostate gland growth, and that can lead to difficulty emptying the bladder and to the need to visit the bathroom frequently. It might also foster the growth of prostate cancer.

These are issues best discussed with a man’s personal doctor if he wants to take testosterone in tablet form.

DEAR DR. DONOHUE: I was diagnosed as having a meningioma brain tumor. I was told it was slow-growing. Was I told that to ease my concerns? Are meningiomas ever malignant? – C.J.

Strictly speaking, meningiomas are not brain tumors. They are tumors of the meninges, the covering layers of the brain. Because of their close proximity to the brain, they are often called brain tumors.

Meningiomas are slow-growing tumors. You were not told that to ease your mind. Most meningiomas are silent. They produce symptoms only if they enlarge and press on important brain centers. My mother had one diagnosed at age 60. She died at age 85 without her meningioma ever having caused a single problem.

A small percentage of meningiomas are malignant, meaning they grow rapidly and spread to other parts of the body. Those are the exceptions to the rule.

If a meningioma does not grow fast and if it is not pressing on important parts of the brain, then it can be observed without taking any drastic steps to remove it.

DEAR DR. DONOHUE: What suggestions do you have for a black tongue? I can clean it off with hydrogen peroxide, but it pops up again in about two weeks. What causes it? Is it a serious problem? Can it be dealt with? – M.M.

People discover their tongues have turned black not because they have any symptoms but because they happen to look in a mirror and see a tongue whose surface has darkened. It freaks them out.

Tiny projections called papillae stud the tongue’s surface. Black tongue results from a rapid growth of those papillae. The elongated papillae trap materials, like food particles, that turn the tongue black.

A black tongue is not an indication of trouble.

If a person wants to get rid of it, using a soft toothbrush and baking soda often gets the job done. Your hydrogen peroxide is another way to attack it.

Black tongues disappear as mysteriously as they appeared. Don’t lose patience.

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.

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