DEAR DR. DONOHUE: I can spend, at most, a half-hour a day in exercise, and it’s not the kind of exercise that leaves me in a sweat. My husband says I’m wasting my time. He says I have to exercise longer and harder. He has a cousin, a woman, who runs marathons. I have no intention of ever doing that. If I have to put so much effort into exercise to get health benefits, I might as well stop what I am doing now. – P.L.

ANSWER: Don’t stop. You don’t have to be at the marathon level of fitness to benefit from exercise. Modest amounts do wonders. If you can walk a little less than two miles in half an hour, you decrease your risk of having a heart attack or stroke, you control your weight and blood sugar, you lower your cholesterol, and you prevent osteoporosis. You need to do this amount of exercise on as many days of the week as you can. I don’t know a single medicine that provides such health benefits.

Even if you walk slower than two miles in half an hour, you still reap benefits. This applies to people with known heart disease and to people who have already had a heart attack, if their doctors approve.

If you want to read a sensible, well-written book on exercise, pick up “The No Sweat Exercise Plan” by Harvey Simon. It’s published by McGraw-Hill. Your local library likely has a copy. If not, the librarian can borrow one from another library.

DEAR DR. DONOHUE: Do you know what forced repetitions are? Are they good for you? I am into weightlifting with three others. We work out together. One of my buddies is trying to get us to use forced repetitions to build strength fast. I know nothing about this. What do you think? – W.S.

ANSWER: Many strength builders lift weights to the point where they cannot perform one more lift. That’s called lifting to the point of failure.

Forced repetitions are lifts done after the point of failure by enlisting the help of another.

I’m not convinced that there is solid evidence that forced repetitions build strength any faster than the more routine approaches to weightlifting.

DEAR DR. DONOHUE: My daughter has a problem with stinky feet. She wears white socks and changes her socks every day. We have tried all sorts of powders and sprays, but they have not helped. Her feet smell bad even when she wears flip-flops. What can we do? – S.T.

ANSWER: Your daughter shares a problem with many athletes. There are 250,000 sweat glands on the feet, and some people are prodigious sweat producers. Wet feet encased in shoes with poor ventilation are breeding grounds for bacteria that produce some awful odors.

Look at the bottoms of your daughter’s feet. If there are white patches of skin on the bottoms of her heels, the balls of her feet and the bottoms of her toes, and if those patches have tiny holes as though a very fine pick had made them, she could have pitted keratolysis, a condition that produces malodorous feet. She should have two pairs of shoes, which she wears on alternate days. She needs to carry a change of socks with her to school so she can switch socks twice a day, three times if possible. She has to wash her feet two times a day, and after washing she should spray her soles with an antiperspirant containing aluminum chloride. If that doesn’t stop her sweating, she’ll need a stronger solution of aluminum chloride, a 20 percent solution (Drysol), which calls for a prescription. After two weeks, if there is no change, she should get a prescription for a solution of erythromycin or clindamycin, two antibiotics. Applying them to her soles will rid her feet of bacteria. All of this applies, even if she doesn’t have pitted keratolysis.

While flip-flops provide air exposure to the feet, they are not good absorbers of sweat. Socks that wick sweat away from the feet are best. Synthetic fibers work well. Acrylic is an example. Or a blend of wool or alpaca with synthetic fibers does a good job of keeping feet dry.

I used to think cotton was the best kind of sock material. Apparently, I was wrong.

DEAR DR. DONOHUE: I have iron-deficiency anemia. Will I be anemic for the rest of my life? I am a 57-year-old female, five years past menopause. Some months ago, I became out of breath while playing tennis. My family doctor had my blood checked, with the enclosed results. Which of these tests convinced my doctor I was bleeding someplace? I am now on iron. I have had my stools checked for blood, and there was none. I have had gastroscopy, colonoscopy and a barium enema. All are normal. I feel fine. – E.B.

ANSWER: If you’re like most iron-deficient people, you won’t be anemic for the rest of your life. On your panel of blood tests, your ferritin is low. Ferritin is protein that acts as a storage bin for iron, so you have to replenish your iron supply, which you’re doing with your iron pills. Your hemoglobin and hematocrit are a trifle low. They indicate a deficiency of red blood cells. The definition of anemia is a low red blood cell count.

An iron shortage comes about because the diet isn’t providing enough of it or the digestive tract can’t absorb it. The third and most important cause is bleeding, most often from the digestive tract and most often not recognized by the patient. Your scope exams and barium enema have pretty much ruled out the digestive tract as a source of bleeding. If you were still menstruating, loss of menstrual blood could be an explanation. Between 2 percent and 5 percent of menstruating women are iron deficient and anemic.

Now that you’re on iron, the deficiency should be corrected in short order and your blood picture should return to normal. If it doesn’t, then the doctor has to look for the poor-iron-absorption causes of anemia. Celiac disease and a stomach-acid deficit are two such causes.

My guess is that your iron pill will cure your anemia and that the anemia came about because your diet was lacking in iron.

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