DEAR DR. DONOHUE: About a month ago, I started getting muscle cramps at night. The cramps are in my calf, thigh or instep. They’re painful. What causes them, and what alleviates them? Could fish oil contribute to cramps? – G.S.

ANSWER: A cramp is a sudden, violent, sustained, painful and involuntary contraction of a muscle. Nighttime cramps can happen to any muscle, but most often they occur in the calves. No one knows for sure what causes them. Older people are the ones who get them the most, so aging must have something to do with them. In a few instances they’re associated with diabetes, a sluggish thyroid gland, poor circulation or pregnancy. Fish oil is not a likely cause.

Loosen your bedcovers. When sleeping on the back, tight covers drag the feet downward, and that promotes cramping.

Stretching the leg muscles can often prevent cramps. Stand 2 or 3 feet from a wall with one foot slightly in front of the other. Lean into the wall and support yourself by bracing your body with your forearms against the wall. You should feel a stretch in the muscles of the leg whose foot is farther from the wall. Hold the stretch for 20 seconds. Resume the upright position and switch foot positions. Do 10 stretches with each foot. If 10 are too many, do what you can. Stretch a couple of times during the day and again before going to bed. While you’re mastering the technique, have a partner at your side to catch you if you become unbalanced.

Medicines that have been touted as cures include quinine, verapamil and diltiazem. None has won a trophy for being a surefire remedy.

At one time, there was a hubbub that the combination of vitamins B-1, 2, 6 and 12, when taken for three months, would put an end to cramps. The hubbub has quieted, but if you want to try them, they won’t hurt so long as you stay within the recommended daily doses found on most vitamin-supplement labels.

The booklet on nighttime cramps and restless leg syndrome gives an overview of these conditions. To obtain a copy, write to: Dr. Donohue – No. 306, Box 536475, Orlando, FL 32853-6475. Enclose a check or money order (no cash) for $4.75 U.S./$6.75 Can. with the recipient’s printed name and address. Please allow four weeks for delivery.

DEAR DR. DONOHUE: I had my fasting blood sugar checked three years ago. It was 108, and the report called it normal, with normal being 70 to 110. This year I had it checked, and it was 106. The report said “impaired glucose tolerance.” What’s going on? Why would it be normal before and not now? – J.C.

ANSWER: In 2003, the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus lowered the upper limit of normal from 110 mg/dL (6.1 mmol/L) to 100 (5.6 /L) because it found that 30 percent of people whose blood sugar was between 100 and 125 (6.9) would develop diabetes within five years. The 110 level was too high to be considered normal. People whose fasting blood sugar is between 100 and 125 are said to have glucose intolerance. One important step these people should take is weight loss – if indicated.

DEAR DR. DONOHUE: I believe that, in some cases, eczema is an allergic reaction to certain foods. My ex-wife, at age 23, had eczema of her hands. She tried everything. A television show turned her into a vegetarian, and she became a devout vegan. After about two months she had only two minor outbreaks. After six months, she had no outbreaks. Maybe others would benefit from this information. – R.C.

ANSWER: Eczema is an intensely itchy skin condition where tiny blisters break out on red patches of skin. I can’t find any evidence that the usual form of eczema comes from food allergy.

A kind of eczema that begins in childhood, atopic dermatitis, is partly due to environmental factors, partly due to genes and partly due to the immune system. Allergies might have something to do with it. There are doctors who say that food allergies are responsible for a few cases. The most-often-implicated foods are nuts, fish, eggs, milk, wheat and soy.

I don’t know why your ex-wife’s eczema responded to a vegetarian diet, but I believe you. I don’t want readers to believe that all will respond similarly.

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.