DEAR DR. DONOHUE: My grandson is very involved in weight training. He is 20 years old, 5 feet 10 inches tall and weighs 165 pounds. He has begun taking a supplement called creatine. I am 66 years old and have lifted weights for 30 years. Four years ago, I was diagnosed with non-Hodgkin’s lymphoma. My grandson is trying to convince me that creatine is safe. Is it? What negative effects could it have on my grandson? How about on me? – C.Z.

ANSWER: Athletes taking anything with an unfamiliar name makes parents and grandparents shudder. They wonder if the athletes are taking something that imperils their health or gets them in trouble with the law. Creatine does neither. It is not a drug. It is not a steroid. It is not a banned substance. It’s the product of amino acids, just like proteins are the products of amino acids. It’s found naturally in muscle cells and in meat. It should be considered a supplement, like a protein or amino acid supplement.

Creatine is a source of energy for muscles. It’s been studied in many institutions and by many reputable scientists, and no one, as yet, has found evidence that it harms users. Most have demonstrated that it builds muscle strength and size by allowing athletes to endure more high-intensity, short-duration exercise, like weightlifting, than can nonusers.

As for side effects, they’re few. In high amounts, it can upset the stomach and might cause diarrhea and stomach cramps. The recommended amount is .14 grams per pound of body weight (.3 grams/kg) for the first five days. Then the amount is decreased to .014 grams per pound (.03 grams/kg). For someone who weighs 185 pounds, that would be 25 grams a day in divided doses for the first five days and 2.5 grams a day thereafter. One ounce is 28 grams.

As for you, I don’t know. You have successfully weathered a battle with cancer. I can’t find any studies done using creatine in people who have had cancer. I wouldn’t take a chance on anything, if I were you, unless your cancer doctor approves.

DEAR DR. DONOHUE: I am a 48-year-old man who has been active from age 20 to now. I average two to six miles of walking or running a day. About four months ago, I developed a problem that scares me. After about a mile and three-quarters, just when I begin to sweat, I develop a rapid and irregular heartbeat. This funny beat goes on for about three to five minutes, and then my heart settles back to normal. I have had all sorts of heart tests, including a 24-hour monitor, but nothing shows up. I have yet to take a treadmill test.

Do you have any idea what’s causing this? Is this a sign of a heart attack? – P.I.

ANSWER: It could well be exercise-induced atrial fibrillation. Atrial fibrillation is a rapid, irregular heartbeat. It is a potentially dangerous heart rhythm whose nature must be discovered. Don’t exercise until you have that treadmill test. It should provoke a bout of the same rhythm, which will show up on the electrocardiogram that’s running from your first step of exercise.

DEAR DR. DONOHUE: I have heard pros and cons on the subject I present to you. Is it better to exercise before or after eating? By exercise, I mean walking. – L.M.

ANSWER: That depends on the size of the meal and your walking pace. If you walk at a moderate pace, you can walk either before or after a meal. Some say exercise decreases the appetite, but I don’t know about that. If you walk fast or eat a very large meal, it would be better not to walk right after eating. Blood gets diverted from the digestive tract to the exercising muscles, and that impedes digestion.

I answered this same question previously about swimming, and many were horrified when I said you can swim after eating. I didn’t mean that you could swim after eating a Thanksgiving-size meal, but you can swim after eating a light meal.

DEAR DR. DONOHUE: My daughter is 65 years old and has a problem with scoliosis. She got it when she was 50. What can be done for it? She exercises every day of her life, a full hour. – B.K.

ANSWER: Scoliosis is a curving of the spine to the right or to the left. The curve can occur in the upper back (chest) section of the spine or in the lower back or in both places. Curvature progresses most rapidly during the growth years. It can worsen in adulthood, but it usually does so slowly.

It’s possible to come down with scoliosis as an adult, but most adult scoliosis had its onset in childhood or adolescence. However, it might be that your daughter never suffered any consequences from it until she was 50.

What to do for an adult with scoliosis and severe back pain hinges on how great the scoliosis curve is. When it approaches 50 degrees, surgical correction is often appropriate. Certainly, back surgery has progressed over the years, and if she needs to have surgery, she should not fear it.

Other considerations for surgical correction are interference with the function of the heart, the lungs or both due to compression caused by the curvature. Your daughter’s exercise program is good, but exercise won’t reverse a curvature at her age.

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.