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!

What does sleep do for us?

DEAR DOCTOR K: Everybody sleeps, but why is that? What does sleep do for us?

DEAR READER: I get this question a lot, and we've talked about it before in this column. There is some new information that is interesting. The honest answer is that we don't know why it is we sleep. We spend about a third of our lives doing it, so nature must have a reason for it. But it's hard to ask nature questions -- or, at least, to get an answer. One possible reason for sleep is obvious: Our muscles may need the rest. However, the heart is a muscle, and it doesn't rest while we sleep, thank goodness. And like our heart, many of our other organs, such as the liver and kidneys, keep working.

Will melatonin supplements help with jet lag?

DEAR DOCTOR K: My wife and I are traveling to Europe in a few weeks, and we're already dreading the jet lag. Do you think melatonin will help?

DEAR READER: Many people find that crossing several time zones makes their internal clocks go haywire. Some small studies have suggested that melatonin can help jet lag if taken a few days before and after travel. Melatonin is a natural substance released by our brain to help coordinate our circadian (day/night) rhythm. This rhythm is disturbed when we travel across time zones. Melatonin is more effective in minimizing the effects on sleep of eastward travel.

How can I get my 9-month-old to sleep through the night?

DEAR DOCTOR K: My 9-month-old is still waking up three to four times during the night. How can I get her to sleep through the night?

DEAR READER: By the time a baby is 4 or 5 months old, he or she is capable of sleeping through the night. We tend to think of "sleeping through the night" as a long stretch of uninterrupted sleep. But in reality, all babies wake up during the night. Some discover their own way of comforting themselves and getting back to sleep. Others must be taught. Different experts recommend different techniques for helping your baby get to sleep and then to sleep through the night.

Are mouth guards an effective treatment for sleep apnea?

DEAR DOCTOR K: I have sleep apnea, and I don't particularly like the CPAP treatment. I've heard that night guards might be an effective alternative. What can you tell me?

DEAR READER: One way or another, getting treatment for sleep apnea is really important. Untreated, sleep apnea increases your risk for high blood pressure, stroke and early death. The airways of people with obstructive sleep apnea narrow as they sleep, and air struggles to get through. People with this condition may breathe shallowly or stop breathing several times an hour.

How can I stop my son from sleepwalking?

DEAR DOCTOR K: My 8-year-old son has started sleepwalking. I'm worried he will hurt himself in his sleep. Is there anything I can do to stop him from sleepwalking?

DEAR READER: A person who is sleepwalking walks or makes other movements while being still largely asleep. A sleepwalker can be difficult to awaken fully and typically has no memory of the episode in the morning. I hope it will ease your worry to know that episodes of sleepwalking are usually brief and harmless.

What does snoring have to do with heart disease?

DEAR DOCTOR K: At my last checkup, my doctor asked if I snore. When I told the doctor that my husband says I snore a lot, the doctor said snoring can be a sign of heart disease, particularly in postmenopausal women. What does snoring have to do with heart disease?

DEAR READER: Snoring is not a sign of heart disease, but it can be a sign of sleep apnea. And people with sleep apnea are at greater risk for heart disease. Sleep apnea is a condition that causes brief, repeated pauses in breathing throughout the night.

Do children who sleep less weigh more?

DEAR DOCTOR K: I recently saw a headline that said children who sleep less weigh more. Is that true? How much sleep should my preschooler and first-grader get each night?

DEAR READER: I believe you're referring to a study recently published in the medical journal Pediatrics. Researchers found that children who don't get enough sleep may also have a higher risk of being overweight. Researchers from Harvard-affiliated Massachusetts General Hospital for Children kept track of more than 1,000 children from the ages of 6 months to 7 years. They asked mothers how much sleep their children got at the age of 6 months, 1 year, and then every year until the end of the study.

Is there a surgical fix for obstructive sleep apnea?

DEAR DOCTOR K: Is there a surgical fix for sleep apnea? I've tried CPAP and a couple of other treatments, and none of them work well for me.

DEAR READER: Sleep apnea is a condition in which breathing stops intermittently, or becomes shallower, during sleep. Obstructive sleep apnea (OSA) is the most common form. OSA occurs when muscles in the back of your throat relax as you sleep. This causes the airway -- the space in the back of your throat through which air passes when you breathe -- to periodically collapse. If air can't get into your lungs, oxygen levels in your lungs drop, which then causes oxygen levels in your blood to drop.

Is periodic limb movement disorder and restless leg syndrome the same thing?

DEAR DOCTOR K: Can you discuss periodic limb movement disorder? Is it the same as restless legs syndrome?

DEAR READER: Restless legs syndrome (RLS) and periodic limb movement disorder (PLMD) are similar disorders, and often (but not always) occur together. RLS causes a wide range of uncomfortable leg sensations. They tend to occur most often when the legs are at rest during the day or in the evening. The sensations are almost always accompanied by an irresistible need to move the legs. Moving the legs can bring temporary relief.