DEAR DR. DONOHUE: My wife is in her 40s and is healthy. Her doctor found out that her vitamin D level is very low and put her on a very high dose of vitamin D. What is vitamin D for, and what happens if you don’t get enough of it? — P.K.

 ANSWER: A deluge of questions arrive daily about vitamin D. I wrote about it last week, but it’s a topic worth repeating.

 When the ultraviolet rays of the sun strike the skin, they change an embryonic form of vitamin D into vitamin D-3. The liver converts D-3 to vitamin D-2. Then the kidneys convert D-2 into active vitamin D. One the vitamin’s chief jobs is to enhance the absorption of calcium so that bones become and remain strong. In the bad old days, when vitamin D was hard to come by, a deficiency led to rickets in children and osteomalacia in adults. Both come from insufficient calcium incorporation into bones. Rickets leaves children with soft bones and bowed legs. Osteomalacia causes bone pain, broken bones and muscle weakness. Neither is seen to the extent they once were. Osteoporosis is a little like osteomalacia, but they are two different processes. A deficiency of vitamin D also contributes to osteoporosis.

 Few foods, unless they are fortified with the vitamin, have much vitamin D in them. People living in northern climates make little to no vitamin D in the winter because their exposure to sunlight isn’t great. Older people can become deficient because their skin doesn’t respond to sunlight as it does in younger days and because the amount of the skin’s vitamin D precursor has diminished. At least one-third of adults has a vitamin D deficiency, and even more elderly people have too little of the vitamin stored in their bodies.

 Vitamin D has other important functions. It lowers blood pressure and prevents diabetes. It might be involved in maintaining heart health, but this is something that requires more proof.

 Restoring the body’s depot of vitamin D requires taking high doses — 50,000 IU once a week for six to eight weeks. After that, the daily recommended intake is 1,000 IU.

 DEAR DR. DONOHUE: Through blood testing, my doctor discovered that my vitamin D level was low. He prescribed tablets containing 50,000 IU. I am very nervous about taking such a high dose. Could it further damage my kidneys, which are functioning at only 39 percent of normal? — N.P.

 ANSWER: High doses of vitamin D taken for prolonged periods can impair kidney function and can raise blood calcium to a too-high level. The high doses you mention are not taken for a long time. Usually they’re given once a week for six to eight weeks.

 At that point, the daily dose is 1,000 IU, a dose higher than the official recommendations that now stand. Those old, official recommendations are considered to be inadequate, and new standards are going to be published.

 DEAR DR. DONOHUE: I am writing because I can’t get help from anyone. I am in good health and sexually active. I am 67 years old.

 My problem is that I am starting to have a low sperm count. What can I do to build up my sperm? I feel like I am half a man. Please let me know. — C.

 ANSWER: I don’t believe you mean sperm count. Sperm counts are done to check a man’s fertility, the ability to father a child. They require microscopic examination of seminal fluid. You’re not wanting to become a father at 67, are you? Men can have children at older ages, but the chances are far less than they are in younger years. Sperm production declines with age.

 I believe you’re talking about the volume of seminal fluid. Age also contributes to a decline of it. Most of the semen is produced by structures called the seminal vesicles and by the prostate gland. The volume of seminal fluid has little to do with sexual potency. Nothing can be done to increase its volume. A lessening of the amount of seminal fluid should not affect relations and should not be considered a health problem.

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.

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