DEAR DR. DONOHUE: My problem is arthritis. I was told that it is hereditary and that there is not much to do for it. I am not taking any medication right now, but I do feel better in hot, dry weather. I go to a YMCA gym regularly and swim, and I think it makes me feel better. Should I follow any particular diet or exercise program? – D.O.

ANSWER: I am basing this answer on the inference that you have osteoarthritis, the most common kind of arthritis. It strikes many older people. It’s due to cracks that occur in joint cartilage. The cracks lead to fraying of the cartilage. Joint cartilage covers the ends of the two abutting bones that form the joint. It’s sort of a Teflon coat for them and enables them to glide over one another without painful friction.

There is much that can be done for osteoarthritis. Exercise is most important. Exercise preserves joint mobility and strengthens muscles that surround the joint. Strong muscles take pressure off the joint.

Swimming is a perfect exercise for people with osteoarthritis. Water buoys the body and cushions joints. It allows people to put many joints through their full range of motion and keeps them limber.

You ask about a specific exercise program. If what you are currently doing helps you, keep with it. If you need more advice, have you inquired at your YMCA? Some Y’s sponsor exercise programs for arthritics. A physical therapist can devise a tailor-made program for you.

There is no special diet for osteoarthritis. A weight-reduction diet is important for those who need to lose some pounds.

Vitamin C and vitamin D are said to retard the progression of osteoarthritis, so you should pay attention to getting the recommended daily allotment of those vitamins. That’s 75 mg of vitamin C for an adult woman and 90 for an adult man. The vitamin D requirement for men and women is 400 IU up to age 70 and 600 IU after 70.

DEAR DR. DONOHUE: Over the past year or so, my otherwise-healthy 15-year-old son has had several episodes where he passes out. It always happens when he stands up suddenly from lying down. I did take him to the doctor for an exam, and he checked the boy’s blood pressure to see if it dropped when he stood up after lying down. It didn’t. The doctor offered no explanation for these episodes. Shouldn’t a healthy teenage male be able to compensate quickly when he changes positions? – J.T.

ANSWER: A healthy teenager should be able to compensate quickly for a change in position, as should a healthy adult. Upon rising from the lying position, blood pools in the legs. That effectively takes a considerable amount of blood out of the circulation. To compensate, the body constricts arteries and increases the heart rate to keep blood pressure up. A drop in pressure deprives the brain of its share of blood, and a person whose pressure suddenly falls can faint.

Even though your son’s pressure didn’t fall on one testing after he rose from lying down, I believe a youngster who has had many such episodes should have a more extensive examination to see if his autonomic nervous system is working normally. It’s the autonomic nervous system that makes body adjustments that keep pressure up when there is a sudden change of position.

He should be examined for other causes of fainting, too.

DEAR DR. DONOHUE: I have tingling and burning on my left thigh when I stand or walk for any prolonged time. What is your assessment of this condition? – E.E.

ANSWER: It could be meralgia paresthetica – pressure on a nerve that serves the upper, outer part of the thigh, roughly the area covered by a cowboy’s hanging gun holster. Pressure on the nerve causes burning pain and skin sensitivity.

Obesity and tight garments, including belts, can be the source of pressure. A doctor can block the nerve with an injection of both lidocaine, a numbing agent, and cortisone, an anti-inflammatory drug. If the injection does not take the pain away, surgically freeing the nerve from whatever is constricting it usually does so.

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.