DEAR DR. DONOHUE: What causes leg cramps? They happen to me in bed almost every night. The pain is so bad it always wakes me. – F.M.

DEAR DR. DONOHUE: I speak for countless senior citizens. Severe, nocturnal leg cramps blow me out of bed each night. Is relief possible? – J.M.

ANSWER: A cramp is a sudden, intense and involuntary muscle contraction. Nighttime leg cramps are a common problem of older people. By age 60, one-third suffer from them; by age 80, half have them. Their cause often escapes detection, but a search for some of the more common causes must be made.

Medicines sometimes are their basis. Diuretics (water pills), beta agonists (asthma medicines), cortisone drugs, statins (for cholesterol control), lithium and nifedipine are potential troublemakers.

Kidney failure; diabetes; thyroid gland malfunction; anemia; a deficiency of magnesium, calcium or potassium; and some nerve disorders are other possible causes. However, for most, a cause cannot be found.

Stretching the leg muscles is a prevention everyone can take. Standing three feet from a wall, lean into it by bracing yourself with your hands on the wall. Keep the feet flat on the floor. You should feel a stretch in the calf muscles. Hold this position for 10 seconds and then return to the starting position for a five-second rest. Repeat the procedure five to 10 times, three times a day, and again before going to bed. For safety’s sake, have a spotter alongside you to catch you if you are on the verge of tumbling.

Loosen the sheets and blankets. When a person lies on his or her back, tight bedding pulls the foot downward, and that induces a cramp.

If the cramps are relentless, speak with your doctor about the use of quinine. It used to be available over the counter but now requires a prescription, because it can have some serious side effects. Verapamil is another medicine that has eased leg cramps for some.

The pamphlet on restless leg syndrome and nighttime cramps offers additional suggestions. Readers can obtain a copy by writing: Dr. Donohue — No. 306, Box 536475, Orlando, FL 32853-6475. Enclose a check or money order (no cash) for $4.50 U.S./$6.50 Can. with the recipient’s printed name and address. Please allow four weeks for delivery.

DEAR DR. DONOHUE: I am 86 and have a history of high blood pressure. This March I began taking magnesium. My blood pressure came down beautifully, and it helped me sleep. I haven’t seen much on magnesium. I would be interested in your view on it. – I.H.

ANSWER: The relationship between magnesium and blood pressure is intriguing. There is evidence that it lowers blood pressure for some people, but the present state of knowledge is not great enough to support general recommendations for its use by all those with high blood pressure.

Women older than 30 need 320 mg (13.3 mmol) a day; men of the same age, 420 (17.5).

You can eat all the magnesium-rich foods you want every day without getting into trouble. They include green, leafy vegetables, beans, nuts, unpolished grains, meat, milk, fruits and eggs. The amount taken as a supplement, however, should not exceed 350 mg (14.6 mmol).

DEAR DR. DONOHUE: I am concerned for my uncle, who had bypass surgeries. He has diabetes and has to watch out for sugar. He avoids cholesterol foods and fatty foods. Now they say he has too much potassium, and he is on a very restricted diet for that. What would you say about this? – Anon.

ANSWER: It’s unusual for diet, by itself, without an associated medical problem, to raise blood potassium levels. Perhaps his high level was a lab error caused by jostling of the blood on its way to the lab. Damaged blood cells leak potassium and cause a false elevation. He should have the test repeated.

Your uncle needs a dietitian or nutritionist. His dietary proscriptions are too complicated for an ordinary person to cope with. His local hospital can provide him with a referral to either of these food specialists.

DEAR DR. DONOHUE: Please say something about Addison’s disease. I have a dear relative who has it, and I am worried sick about her.

Will she die from it? – N.G.

ANSWER: Addison’s disease is the illness where the adrenal glands’ production of their hormones either stops or is greatly diminished. The adrenal glands are two in number. One is on top of the right kidney, and the other on the left.

Your relative’s worst days are over. Those were the days before the disease was diagnosed. Now that it has been, the missing hormones can be supplied as pills or tablets, and she should be feeling her old self in a short time. She should not die from it.

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.