DEAR DR. DONOHUE: I have a question about body temperature. Normally, mine is under 97 F. I understand from my doctor that this is fine, because the normal of 98.6 is an average, with some people having a lower and some a higher temperature.

My question is: At what temperature do I have a fever? When I have a temperature of 99.5, I generally feel quite ill. My doctor says that is not considered a fever. A “fever” is a temperature of 100 or higher. Isn’t a temperature of 100 for me equivalent to a temperature of 102 for someone whose body temperature is the typical 98.6? — Anon.

ANSWER: Body temperature fluctuates throughout the day and depends on what the person is doing. Activity increases body temperature. Low temperature normally occurs around 6 a.m., and higher ones between 4 p.m and 6 p.m.

Are you taking oral body temperatures? Oral readings always register lower than other sites for taking temperature because of mouth breathing.

Some people do have a body temperature consistently lower than 98.6 (37 C), and others have one consistently higher. These people have thermostats set at a different level from the rest of us.

In people whose temperature is closer to 98.6 most of the time, a temperature of 100 (37.8) is considered abnormal and a fever. That’s 1.4 degrees above 98.6 (0.8 degree above 37). If you are taking your temperature correctly and it truly does hover around 97 most of the time, a fever for you would be 97 plus 1.4: 98.4.

Body temperature is only one sign of illness. Other signs are just as reliable — a hacking cough, feeling done in, feeling warmer than normal, having diarrhea, having a cough, having a headache, having a faster heartbeat. You can tell when you’re sick without ever using a thermometer.

DEAR DR. DONOHUE: My stomach doesn’t tolerate fresh fruits or vegetables. Are frozen or canned ones just as beneficial? — J.P.

ANSWER: After being picked, fruits and vegetables are frozen quickly — more quickly than the produce that’s transported to a grocery store. Frozen fruits and vegetables retain their vitamins, minerals and other nutrients.

Canned foods also are processed rapidly after they’re picked. They, too, keep much of what nature put in them.

If you raise your own fruits and vegetables, pick and then eat them right away, you are getting the most nutrition possible. Not many of us eat in this fashion.

DEAR DR. DONOHUE: Three years ago, my 59-year-old niece was a fun-loving, talkative, happy-go-lucky person. Today she acts as if she is in a trance. She doesn’t smile, and answers you with “yes,” ”no” or “I don’t know.”

She has had all kinds of tests. Physically, she is OK. She’s been told she has a chemical imbalance. What causes such a turnaround? She sees a psychiatrist and is on medication. Is there any hope for her? — M.S.

ANSWER: Your niece is depressed. In the modern view, depression comes from an upset in the normal production of brain messenger chemicals. Their names are serotonin, norepinephrine and dopamine. That’s the chemical imbalance your niece has.

Medicines can restore the balance. Usually, medicines are combined with sessions with a mental health professional like a psychiatrist. I can’t deny that three years is an awfully long time for a depression to linger. Perhaps your niece would benefit from a change of medicines, treatment and doctor.

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.