At what age do I need to start regular exercise?

DEAR DOCTOR K: I believe you when you say that regular exercise protects my health. But I'm just 20. For me the question is, when should I begin regular exercise? The diseases that exercise protects against usually don't develop until a person is older than 60. I'd like not to have to worry about exercise for a few decades.

DEAR READER: I wish I could rid you of that worry. But, in fact, if you are not already exercising regularly, you are probably putting your health at risk 30 years from now. Many of the diseases that exercise protects against actually start in young adulthood and take decades to become severe enough to cause symptoms. For example, autopsy studies have been performed on soldiers killed in war -- people your age. They reveal that many already have early signs of atherosclerosis, the cause of heart attacks, strokes and premature death.

Do I need a daily medicine to prevent gout?

DEAR DOCTOR K: I have had three attacks of gout in the past year. I never had it before. Now my doctor wants me to take a medicine every day, even though I feel fine. Is this a good idea?

DEAR READER: Well, you have a kindred soul in Doctor K, since I also have developed gout in recent years. The disease occurs when a natural chemical called uric acid finds its way into the joints that connect two bones. All of us always have some amount of uric acid in our blood. In people with gout, the amount of uric acid usually is higher than normal.

I have a heart condition. What do I need to know before I get pregnant?

DEAR DOCTOR K: I have a heart condition. What do I need to know before I get pregnant?

DEAR READER: When a woman is pregnant, her heart is working for two. Blood passes through her placenta to her baby. This places additional demands on her body's circulatory system, particularly the heart. Among other changes, her heart pumps a much higher volume of blood each minute. As a woman with a heart condition, it's particularly important for you to understand what this added workload might mean to your health, and to your baby's.

What is sepsis?

DEAR DOCTOR K: My father had routine surgery. Soon after, he developed something called sepsis that almost killed him. He's OK now, but I'd like to understand what happened to him.

DEAR READER: He and you are lucky. Not everyone makes it. Sepsis is a condition in which the immune system goes awry. Think of the immune system as our personal army, with an arsenal of weapons. It is meant to protect us from foreign invaders (like germs). Unfortunately, in attacking foreign germs, it sometimes can go overboard -- and its weapons can injure us.

Do I need to take medication for BPH?

DEAR DOCTOR K: I have BPH. The symptoms don't interfere with my work or home life very much. My doctor says there are medicines that might reduce the symptoms, but I like to avoid taking medicines. What's your advice?

DEAR READER: Benign prostatic hyperplasia, or BPH, is the most common cause of prostate enlargement. As the name suggests, BPH is harmless; it does not lead to prostate cancer.

What is sundowning?

DEAR DOCTOR K: My husband and I are in our early 80s. Sometimes in the evening he is agitated, confused, and just quite a handful to deal with. The doctor says he has "sundowning." What is it, and is there anything I can do?

DEAR READER: Some older people have trouble concentrating, grow agitated or even confused, and become especially fatigued at the end of the day. This phenomenon is known as "sundowning" because its effects tend to coincide with sunset -- usually occurring in the late afternoon into the evening, then settling down late at night.

What types of joints are available for a knee replacement?

DEAR DOCTOR K: I am going to have my knee replaced. What types of artificial knee joints are available?

DEAR READER: The knee is a joint formed by the bottom end of the thigh bone and the top ends of two bones of the lower leg. When the ends of the bones that form the joint become damaged, they can be removed and replaced. That's total knee replacement, and it is major surgery.

Is it dangerous to sleep too much?

DEAR DOCTOR K: I've heard a lot about the harmful effects of insufficient sleep. But are there any dangers of sleeping too much?

DEAR READER: Over the years we've learned that sleep is important for a variety of reasons. It appears to be vital for forming long-term memories. It also helps you to digest what you have learned the previous day. Sleep promotes concentration and restores energy; it helps to keep your immune system functioning well and to regulate eating patterns.

Is there any way to prevent deep-vein thrombosis during travel?

DEAR DOCTOR K: A friend of mine recently developed a blood clot in his leg after a long flight. I travel a lot for work, so this has me worried. Is there any way to prevent this type of thing?

DEAR READER: A blood clot that forms deep inside a leg vein, known as deep-vein thrombosis (DVT), can cause pain, swelling and redness in the affected limb. But the real threat happens if the clot breaks off and travels to the lungs. Known as a pulmonary embolism, this can lead to sudden death. (I've put an illustration of this process on my website,