DEAR DR. DONOHUE: After a consultation with my doctor for the results of my removed kidney stone and 24-hour urine collection, I was told my calcium is high. Currently I take calcium citrate, vitamin D and Fosamax because of my past bone-density testing. My doctor, as a result of the new tests, has me on a low-sodium, low-calcium diet. He hasn’t consulted my primary physician. How does the decrease in calcium affect my bone density? — S.G.

ANSWER: Your question is similar to one I answered last week. One difference is the 24-hour urine test you had. Often, blood calcium is measured at the same time. If both your blood and urine calcium are high, you have a problem that the previous writer did not have. A search has to be made for the cause of your high blood calcium. In such a case, limiting dietary calcium is helpful only if you were eating a diet very high in calcium. A high blood calcium raises questions of an excess of parathyroid hormone, an overactive thyroid gland, an excess of vitamin D, medicines like thiazide water pills and an illness called sarcoidosis.

If only your urine was high in calcium, a low-calcium diet doesn’t usually help. That sounds paradoxical, but it isn’t. A low calcium intake in such a case actually promotes kidney stone formation.

The low calcium intake could worsen your bone density — the basis of osteoporosis. Each of your doctors — the kidney stone doctor and the one who is treating you for osteoporosis (Fosamax is an osteoporosis medicine) — must know what the other is doing.

Stones can be prevented by drinking lots of fluid. You should drink enough so that your urine is pale yellow or colorless. The low-sodium diet is a good idea. Sodium increases the urine concentration of calcium and favors stone formation.

DEAR DR. DONOHUE: I am responding to the item you wrote about dry eyes causing excessive tears. My wife suffered for a couple of years with such watery eyes that it made her life miserable. She underwent a number of tests and tried a number of remedies, but her watery eyes failed to clear up.

The cure appeared in the form of Systane, which, as you know, is sold over the counter. As soon as she started taking Systane, her watery-eye problem resolved. — S.R.

ANSWER: Dry eyes do cause eye watering. Every case of watering eyes, however, isn’t due to dry eyes. Even if it is, an eye doctor has to be consulted to determine what’s causing the dryness.

I’m happy that your wife found an answer for her problem. Systane eyedrops are an eye lubricant. They aren’t the answer to every case of dry eyes.

DEAR DR. DONOHUE: I feel that the information about swimming in cold water could be misleading. Having boated in Northwest waters for many years, I am aware that the temperature in Canadian waters is frequently in the 50 degree range. If a person swims in water of this temperature and is unable to get out because of being too far from shore, drowning is a grave danger. — D.T., MD

ANSWER: I agree with you, Doctor. Guidelines for holding swim meets advise cancelling the meet if the water temperature is below 57 F (14 C). I wouldn’t think of putting my big toe in water that cold.

DEAR DR. DONOHUE: I would appreciate reading your comments on the current rumor that microwaved food loses all nutritional value. — C.T.

ANSWER: That’s not a current rumor. It’s a piece of misinformation that has been circulating since microwave ovens appeared on the market.

It’s not true. Microwaving preserves vitamins and minerals better than almost any other method of cooking. Foods lose some of their nutritional value when they are boiled in lots of water; the water draws out some vitamins. Little water is used in microwave cooking.

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.