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Sunday, March 1, 2015

HƯỚNG DẪN GIÚP BẠN NGỦ NGON (YOUR GUIDE TO HEALTHY SLEEP)

HOW MUCH SLEEP IS ENOUGH?


Animal studies suggest that sleep is as vital as food for survival. Rats, for example, normally live 2–3 years, but they live only 5 weeks if they are deprived of REM sleep and only 2–3 weeks if they are deprived of all sleep stages—a timeframe similar to death due to starvation. But how much sleep do humans need? To help answer that question, scientists look at how much people sleep when unrestricted, the average amount of sleep among various age groups, and the amount of sleep that studies reveal is necessary to function at your best.

When healthy adults are given unlimited opportunity to sleep, they sleep on average between 8 and 8.5 hours a night. But sleep needs vary from person to person. Some people appear to need only about 7 hours to avoid problem sleepiness, whereas others need 9 or more hours of sleep. Sleep needs also change throughout the life cycle. Newborns sleep between 16 and 18 hours a day, and children in preschool sleep between 11 and 12 hours a day. School-aged children and adolescents need at least 10 hours of sleep each night.

The hormonal influences of puberty tend to shift adolescents’ biological clocks. As a result, teenagers (who need between 9 and 10 hours of sleep a night) are more likely to go to bed later than younger children and adults, and they tend to want to sleep later in the morning. This delayed sleep–wake rhythm conflicts with the early-morning start times of many high schools and helps explain why most teenagers get an average of only 7–7.5 hours of sleep a night.

As people get older, the pattern of sleep also changes—especially the amount of time spent in deep sleep. This explains why children can sleep through loud noises and why they might not wake up when moved. Across the lifespan, the sleep period tends to advance, namely relative to teenagers; older adults tend to go to bed earlier and wake earlier. The quality—but not necessarily the quantity—of deep, non-REM sleep also changes, with a trend toward lighter sleep. The relative percentages of stages of sleep appear to stay mostly constant after infancy. From midlife through late life, people awaken more throughout the night. These sleep disruptions cause older people to lose more and more of stages 1 and 2 non-REM sleep as well as REM sleep.

Some older people complain of difficulty falling asleep, early morning awakenings, frequent and long awakenings during the night, daytime sleepiness, and a lack of refreshing sleep. Many sleep problems, however, are not a natural part of sleep in the elderly. Their sleep complaints may be due, in part, to medical conditions, illnesses, or medications they are taking— all of which can disrupt sleep. In fact, one study found that the prevalence of sleep problems is very low in healthy older adults. Other causes of some of older adults’ sleep complaints are sleep apnea, restless legs syndrome, and other sleep disorders that become more common with age. Also, older people are more likely to have their sleep disrupted by the need to urinate during the night.

Some evidence shows that the biological clock shifts in older people, so they are more apt to go to sleep earlier at night and wake up earlier in the morning. No evidence indicates that older people can get by with less sleep than younger people. (See “Top 10 Sleep Myths”.) Poor sleep in older people may result in excessive daytime sleepiness, attention and memory problems, depressed mood, and overuse of sleeping pills.

Despite variations in sleep quantity and quality, both related to age and between individuals, studies suggest that the optimal amount of sleep needed to perform adequately, avoid a sleep debt, and not have problem sleepiness during the day is about 7–8 hours for adults and at least 10 hours for school-aged children and adolescents. Similar amounts seem to be necessary to avoid an increased risk of developing obesity, diabetes, or cardiovascular diseases.

Quality of sleep and the timing of sleep are as important as quantity. People whose sleep is frequently interrupted or cut short may not get enough of both non-REM sleep and REM sleep. Both types of sleep appear to be crucial for learning and memory—and perhaps for the restorative benefits of healthy sleep, including the growth and repair of cells.

Many people try to make up for lost sleep during the week by sleeping more on the weekends. But if you have lost too much sleep, sleeping in on a weekend does not completely erase your sleep debt. Certainly, sleeping more at the end of a week won’t make up for any poor performance you had earlier in that week. Just one night of inadequate sleep can negatively affect your functioning and mood during at least the next day.

Daytime naps are another strategy some people use to make up for lost sleep during the night. Some evidence shows that short naps (up to an hour) can make up, at least partially, for the sleep missed on the previous night and improve alertness, mood, and work performance. But naps don’t substitute for a good night’s sleep. One study found that a daytime nap after a lack of sleep at night did not fully restore levels of blood sugar to the pattern seen with adequate nighttime sleep. If a nap lasts longer than 20 minutes, you may have a hard time waking up fully. In addition, late afternoon naps can make falling asleep at night more difficult.


Top 10 Sleep Myths

Myth 1: Sleep is a time when your body and brain shut down for rest and relaxation. No evidence shows that any major organ (including the brain) or regulatory system in the body shuts down during sleep. Some physiological processes actually become more active while you sleep. For example, secretion of certain hormones is boosted, and activity of the pathways in the brain linked to learning and memory increases.

Myth 2: Getting just 1 hour less sleep per night than needed will not have any effect on your daytime functioning. This lack of sleep may not make you noticeably sleepy during the day. But even slightly less sleep can affect your ability to think properly and respond quickly, and it can impair your cardiovascular health and energy balance as well as your body’s ability to fight infections, particularly if lack of sleep continues. If you consistently do not get enough sleep, a sleep debt builds up that you can never repay. This sleep debt affects your health and quality of life and makes you feel tired during the day.

Myth 3: Your body adjusts quickly to different sleep schedules. Your biological clock makes you most alert during the daytime and least alert at night. Thus, even if you work the night shift, you will naturally feel sleepy when nighttime comes. Most people can reset their biological clock, but only by appropriately timed cues—and even then, by 1–2 hours per day at best. Consequently, it can take more than a week to adjust to a substantial change in your sleep–wake cycle—for example, when traveling across several time zones or switching from working the day shift to the night shift.

Myth 4: People need less sleep as they get older. Older people don’t need less sleep, but they may get less sleep or find their sleep less refreshing. That’s because as people age, the quality of their sleep changes. Older people are also more likely to have insomnia or other medical conditions that disrupt their sleep.

Myth 5: Extra sleep for one night can cure you of problems with excessive daytime fatigue. Not only is the quantity of sleep important, but also the quality of sleep. Some people sleep 8 or 9 hours a night but don’t feel well rested when they wake up because the quality of their sleep is poor. A number of sleep disorders and other medical conditions affect the quality of sleep. Sleeping more won’t lessen the daytime sleepiness these disorders or conditions cause. However, many of these disorders or conditions can be treated effectively with changes in behavior or with medical therapies. Additionally, one night of increased sleep may not correct multiple nights of inadequate sleep.

Myth 6: You can make up for lost sleep during the week by sleeping more on the weekends. Although this sleeping pattern will help you feel more rested, it will not completely make up for the lack of sleep or correct your sleep debt. This pattern also will not necessarily make up for impaired performance during the week or the physical problems that can result from not sleeping enough. Furthermore, sleeping later on the weekends can affect your biological clock, making it much harder to go to sleep at the right time on Sunday nights and get up early on Monday mornings.

Myth 7: Naps are a waste of time. Although naps are no substitute for a good night’s sleep, they can be restorative and help counter some of the effects of not getting enough sleep at night. Naps can actually help you learn how to do certain tasks quicker. But avoid taking naps later than 3 p.m., particularly if you have trouble falling asleep at night, as late naps can make it harder for you to fall asleep when you go to bed. Also, limit your naps to no longer than 20 minutes, because longer naps will make it harder to wake up and get back in the swing of things. If you take more than one or two planned or unplanned naps during the day, you may have a sleep disorder that should be treated.

Myth 8: Snoring is a normal part of sleep. Snoring during sleep is common, particularly as a person gets older. Evidence is growing that snoring on a regular basis can make you sleepy during the day and increase your risk for diabetes and heart disease. In addition, some studies link frequent snoring to problem behavior and poorer school achievement in children. Loud, frequent snoring also can be a sign of sleep apnea, a serious sleep disorder that should be evaluated and treated. (See “Is Snoring a Problem?”.)

Myth 9: Children who don’t get enough sleep at night will show signs of sleepiness during the day. Unlike adults, children who don’t get enough sleep at night typically become hyperactive, irritable, and inattentive during the day. They also have increased risk of injury and more behavior problems, and their growth rate may be impaired. Sleep debt appears to be quite common during childhood and may be misdiagnosed as attention-deficit hyperactivity disorder.

Myth 10: The main cause of insomnia is worry. Although worry or stress can cause a short bout of insomnia, a persistent inability to fall asleep or stay asleep at night can be caused by a number of other factors. Certain medications and sleep disorders can keep you up at night. Other common causes of insomnia are depression, anxiety disorders, and asthma, arthritis, or other medical conditions with symptoms that tend to be troublesome at night. Some people who have chronic insomnia also appear to be more “revved up” than normal, so it is harder for them to fall asleep.