DEAR DR. DONOHUE: Dairy products are a problem for me. For breakfast, 1 percent milk is fine and yogurt isn’t troublesome. Other dairy foods bother me. I am 61 and more intolerant of dairy foods now than when I was younger. Why? — Anon.

ANSWER: Lactase is an enzyme found in the small intestine. It digests lactose, milk sugar. Infants of all animal species are born with a good supply of the lactase enzyme. They lose their supply of lactase at the time they are weaned from their mother’s milk. Most humans hold onto an adequate supply of lactase into adult life. Some, however, have so little that they find dairy products impossible to digest. Dairy products bloat these people, give them stomach cramps and can bring on diarrhea. That’s lactase deficiency or lactose intolerance. Both terms denote the same problem. The lactase deficiency is an ethnic trait. Blacks, Asian-Americans and Native Americans have less lactase in adulthood than do whites. Age causes the lactase supply to dwindle. That’s the reason you have more trouble at age 61 than you did years ago.

Cheeses and yogurt are exceptions to the rule. Many lactase-deficient people tolerate them well.

You can overcome the lactase deficiency problem by avoiding dairy products, by taking the lactase enzyme in pill form before eating dairy products or by using dairy products that have been pretreated with the enzyme.

DEAR DR. DONOHUE: I used nicotine gum to stop smoking. I have been off cigarettes for a few years now, but I still chew the gum. I chew a couple dozen pieces a day. Am I harming my health? — C.K.

ANSWER: The manufacturers of nicotine gum state that their product shouldn’t be used for more than three months.

There’s no argument that chewing nicotine gum is far less devastating to health than is smoking cigarettes. Cigarettes contain not only nicotine but a raft of many other potentially dangerous compounds. And you are no longer assaulting your lungs — another health benefit.

All the same, nicotine is not on the pyramid of things that promote better health. It constricts arteries and transiently raises blood pressure. It increases the resting heart rate, and that’s a stress the heart doesn’t need. It’s believed to encourage the buildup of plaque on artery walls.

You can break your gum habit. If you can stop suddenly, do so. You might have headaches for a few days. Or you can begin reducing the sticks of gum chewed. Substitute sugarless gum for every other piece of nicotine gum you would put in your mouth. Every second or third day, increase the pieces of sugarless gum and reduce the number of pieces of nicotine gum until you are nicotine-gum-free.

DEAR DR. DONOHUE: I am a concerned grandma regarding my 21-year-old grandson. He doesn’t have any friends. He is tall and very slender. He has no ambitions. He hasn’t finished high school. I think he fears failure in anything he does. He stays in his bedroom. He appears to be on the level of a 13-year-old when it comes to social skills. When he was young, he was diagnosed with attention-deficit disorder, but refused to take any medication. He doesn’t do drugs or smoke. I think something is wrong with him medically. His upbringing was very stressful.

I am not sure what kind of doctor to go to. He has no insurance. — C.P.

ANSWER: The odds point more to psychological problems than physical problems. This young man needs help. I looked it up, and your county has a department of mental health. Start there. Explain the situation just as you explained it to me. Tell the people he has no money or insurance. You also can talk to the county medical society for any programs it might sponsor.

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.