DEAR DR. DONOHUE: I am 60 years old, and I need a heart valve replaced. The doctor explained that because of my age, he would put in a man-made mechanical valve. He says it lasts longer than a pig valve. Can you tell me what the life expectancy is of both valves? – R.E.

ANSWER: Replacing damaged heart valves is one of medicine’s most impressive achievements, and in recent years, the achievement has become even more astonishing with the variety of materials available for replacement valves.

Mechanical valves are made of many durable materials. Their big advantage is their long life span. They last for decades and longer. Their disadvantage is their tendency to form clots. For that reason, a person with a mechanical valve must be on anticoagulants to prevent a devastating complication like a stroke.

Biologic valves come from animals or humans. Animal grafts – xenografts – are popular, and often the pig is the donor source. Their advantage lies in not fostering clots, so they free people from the hassle of having to take anticoagulants. Their disadvantage is their lesser durability. A pig valve lasts for 10 to 15 years and sometimes longer.

If a person’s life expectancy does not exceed the anticipated life of a pig valve, then it is a desirable choice for replacement.

Newer and novel mechanical materials, ones less likely to lead to clots, are undergoing study and trials. For the present, however, these valves require anticoagulation.

The topic of valvular heart disease is a complicated and often misunderstood one. The booklet on that subject can clear the air for people. Readers can obtain a copy by writing: Dr. Donohue – No. 105, 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: This might be a silly question. I know that, when you have a cold, the germ will be active for some time on, say, a doorknob. If you have a cold and write a letter, will the person getting the letter get your cold? – L.M.

ANSWER: Rhinoviruses are the viruses that are responsible for most colds. They can persist on inanimate objects – doorknobs, pens, pencils, paper – for several hours after being deposited there by an infected person. However, transmission from such contact is not the usual way colds are spread.

Hand-to-hand contact usually spreads a cold. An infected person sports a coat of virus on his or her hands. Shaking hands with another transfers the virus from the infected to the uninfected. The newly infected person touches the nose or eyes, and the virus has found entrance to the body and is able to bring on a cold.

Hand washing is the best way to prevent colds and the best way for people with colds to stop their spread.

Aerosolized droplets from a cough or sneeze also spread the virus. Covering the mouth when coughing or sneezing is a humanitarian gesture that the rest of the world greatly appreciates.

Did you have a cold when you wrote me this letter? Not to take any chances, I have washed my hands 13 times after reading it and am now going out to buy some vinyl gloves before reading any more letters.

DEAR DR. DONOHUE: You informed us that a person should take 1,200 mg of calcium a day. My vitamin supplement has 200 mg of calcium in it. Does this allow me to include milk, yogurt or cheese in my diet? I don’t want to overdo calcium. – E.K.

ANSWER: The upper limit for daily calcium is 2,500 mg. You’ve got 1,000 mg left to reach your daily limit and 2,300 mg left before you hit the upper limit. Most people, unless they are extreme devotees of dairy products, don’t come close to getting the recommended daily calcium requirement from food. You don’t have to worry about overdoing things.

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.