Do the microbes that live on our bodies cause heart disease and autism?

DEAR DOCTOR K: You recently wrote that the microbes that live on and within us might be a cause of disease. A friend told me she heard they might cause heart disease and autism. Is there any truth to that?

DEAR READER: For a long time we've known that defects in how our genes are built, and defects in whether our genes are appropriately turned on, powerfully influence whether we develop diseases. However, our human genes may not be the only genes that affect our health. Trillions of germs live on and within us, all of our lives. They live on our skin, in our mouth, in our gut and elsewhere. And they have genes, too. We call their genes, collectively, our "microbiome." Indeed, our microbiome contains about 400 times more genes than we have human genes.

Will my son grow out of his childhood obesity? I don’t want to make a big deal about his eating habits.

DEAR DOCTOR K: My 9-year-old son is very overweight. I don't want to make a big deal about his eating habits, because I assume he'll grow out of his obesity later in life, and because we already set so many rules for him to follow. Do you agree?

DEAR READER: I wish I could, but I can't. A child's eating habits, and weight, can adversely affect his or her health later in life. The healthy eating habits you set with young kids not only influence their eating habits later in life, they also influence the chemistry of your kids' bodies so they are less likely to get fat as adults. All the talk about childhood obesity is not just media hype.

What is it about exercising that promotes good health?

DEAR DOCTOR K: You frequently write that exercising regularly may be the best thing you can do to improve your health. I don't doubt that's true. But have scientists figured out what it is about exercise that promotes health?

DEAR READER: You've asked a very interesting question. Perhaps you're thinking, as do some of my patients, that exercise leads the body to produce certain natural chemicals that promote health. And that if you could make pills out of those health-promoting chemicals, maybe you wouldn't need to exercise. Actually, research here at Harvard in the past few years may have made a step in that direction. The research is primarily in mice, but it probably applies in humans as well.

Any advice for an at-home, do-it-yourself pedicure?

DEAR DOCTOR K: Last time I got a pedicure, I ended up with toenail fungus. I'm not taking another chance. Any advice for an at-home, do-it-yourself pedicure?

DEAR READER: A pedicure is a great way to pamper your feet. But salons don't always maintain the best safety standards, and that can lead to infection. If you're determined to try a do-it-yourself (DIY) pedicure, pick up a basic pedicure kit at your local pharmacy. Then follow these directions: Fill a pan or basin with warm water. Soak your feet for a few minutes, until the skin and nails soften. Dry your feet with a towel.Gently rub a pumice stone against your skin to remove any dead skin cells. Don't rub too hard. Take care of the cuticles. Rub lotion or oil onto your toenails to soften the thin layer of skin at the bottom and sides of your toenail. Gently push the cuticles back to the base of the nails, using an orange stick or a moist washcloth. Don't cut the cuticles; that could lead to infection.

Can osteoporosis medications cause bone fractures?

DEAR DOCTOR K: I'm taking a pill for osteoporosis because my doctor says that stronger bones will reduce my risk of fractures. But a friend recently told me that some osteoporosis medicines actually cause fractures. Can you un-confuse me?

DEAR READER: I know what you're referring to, and it is confusing -- even for doctors. So let me try to make it less confusing. Osteoporosis does make your bones more susceptible to fractures, and a group of drugs called bisphosphonates do successfully treat osteoporosis. These drugs include alendronate (Fosamax), ibandronate (Boniva), risedronate (Actonel) and zoledronic acid (Reclast). People typically remain on these drugs for years.

Why does a boy’s voice change during puberty?

DEAR DOCTOR K: My son is 14, and his voice has started to change. Why does this happen?

DEAR READER: Your son is going through puberty. A change in his voice is just one of several changes in this phase of life. The first thing that generally happens to a boy during puberty is that his testicles begin to get larger and to make testosterone. Then, the penis begins to grow and sexual hair begins to appear. He will become more muscular. He will have more frequent erections, become capable of making sperm and thus become fertile.

How can we prevent brain damage during contact sports?

DEAR DOCTOR K: My kids play contact sports. After all the news about how repeated concussions might cause permanent brain damage, I'm worried. Do doctors understand why the brain damage occurs and how to prevent it?

DEAR READER: People have known for a long time that boxers could develop difficulty with thinking, remembering, balance and mood following the end of their careers. The term "punch-drunk" was often used. After all, they're getting hit in the head constantly and are often knocked unconscious.

What is metabolic syndrome?

DEAR DOCTOR K: My doctor says I have metabolic syndrome. He said it's "like diabetes but not diabetes," which I don't understand. Can you explain what it is, and how I can fix it?

DEAR READER: Metabolic syndrome is quite common, but not very well known. Many of my patients have it; nearly 50 million Americans have it -- and many of them don't know it. Metabolic syndrome is dangerous. If you have it, you have a much higher risk of several major health conditions. Recent studies find that your risk of developing diabetes is four to five times higher. I guess that's what your doctor meant when he said it was "like diabetes but not diabetes." Your risk of stroke or a heart attack is about double. Your risk of dying prematurely is 30 to 60 percent higher.

What happens during a C-section?

DEAR DOCTOR K: My doctor says she is going to have to deliver my baby by C-section. What will happen during this procedure?

DEAR READER: A cesarean delivery, or C-section, is surgery to deliver a baby through the abdomen. It may be scheduled in advance when a woman cannot or should not deliver the baby through the vagina. A C-section may also be performed if continuing with labor or delivery becomes risky to the mother or baby. Finally, a cesarean may be done as an emergency procedure if there is immediate risk to a mother or baby.

Do we need to sleep in order to “flush out” our brain?

DEAR DOCTOR K: A friend told me that the reason we sleep is to "flush out" our brain. What is this all about? Is this the reason we sleep?

DEAR READER: Many readers have written asking why we sleep, and we discussed it in yesterday's column. Today we will talk about the recent study that you are asking about, which suggests that one reason we sleep may be to flush out the brain. For those who didn't read yesterday's column, a quick summary. There is evidence that during sleep, our mind and body benefits in several ways. Perhaps most obvious, our muscles get a rest. The fortunate exception is the special muscle that is our heart. We don't want it to quit pumping -- ever!