DEAR DR. DONOHUE: I am a nurse who is into exercise. This year, I have increased the amount of time I exercise and have increased the exercise difficulty.

I don’t know if this is just a coincidence or if it’s related to my new program: I have had two colds this year, one on top of the other. Could the increase in my exercise routine have weakened my immune system? What do you think? — J.P.

ANSWER: Regular, moderate-intensity exercise enhances the immune system. Exhaustive exercise, on the other hand, lowers body immunity. By exhaustive, I mean on a par with marathon running. After such intensive exercise, it takes the body’s immune system a full week to restore itself.

Such exercise lowers the number of circulating white blood cells. They are an integral part of our defenses against infections. They also are an integral part of the immune system. This high level of exercise also reduces the body’s ability to produce antibodies, another important element in immunity from infections.

I don’t know if you are exercising at that level. I’m more inclined to believe your two colds were just a fluke happenstance and were not due to the increase in time you are spending exercising. You probably had the misfortune of coming into contact with two different cold viruses.

DEAR DR. DONOHUE: Can one safely exercise with a cold? I have taken it for granted that it is better not to do so. I have a friend who says my attitude is wimpy. Is it? — H.L.

ANSWER: If a person who has a cold feels well enough to exercise, then it’s OK to do so. If you work out in a gym with lots of other people close to you, it would be more thoughtful not to exercise, especially if you are sneezing and your nose is running.

The rule of thumb is if cold symptoms are above the neck, it’s OK to exercise. If they’re below the neck — coughing, for example — it’s better not to exercise.

If you have a fever, don’t exercise.

DEAR DR. DONOHUE: I started taking the amino acids arginine, lysine and ornithine to enhance my production of growth hormone and my building-up of muscles. What are your thoughts on this? — P.K.

ANSWER: At one time, the combination of those three amino acids to stimulate growth hormone production was the rage. I haven’t heard of many people still using this combination. I haven’t seen anything written about it.

I don’t know if those amino acids really do increase growth hormone production. I have to believe that it is a minuscule increase if it happens at all.

DEAR DR. DONOHUE: I remember you wrote something about the connection of heavy-duty exercise with kidney damage, but I can’t remember the details. Will you repeat the information? — F.F.

ANSWER: Some time ago, I related a story told to me by a friend who was the team physician for a local high school. One of the school’s athletes was trying to break the record for the number of consecutive sit-ups. He felt fine following the session, but the next morning his abdominal muscles were so sore he could barely get out of bed. He went to school and decided to see the school nurse, who called my friend. The boy’s urine had turned dark brown.

My friend recognized the signs of rhabdomyolysis, a wholesale breakdown of muscle cells with the release of substances that damage kidneys. He admitted the boy to the hospital and treated him. The boy did well and made a full recovery. He’s not trying for any more sit-up records.

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.

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