Sleep was long considered just a uniform block of time when you are not awake. Thanks to sleep studies done over the past several decades, it is now known that sleep has distinctive stages that cycle throughout the night. Your brain stays active throughout sleep, but different things happen during each stage. For instance, certain stages of sleep are needed for us to feel well rested and energetic the next day, and other stages help us learn or make memories.

In brief, a number of vital tasks carried out during sleep help maintain good health and enable people to function at their best. On the other hand, not getting enough sleep can be dangerous-for example, you are more likely to be in a car crash if you drive when you are drowsy.

Sleep needs vary from person to person, and they change throughout the lifecycle. Most adults need 7-8 hours of sleep each night. Newborns, on the other hand, sleep between 16 and 18 hours a day, and children in preschool sleep between 10 and 12 hours a day. School-aged children and teens need at least 9 hours of sleep a night.

Some people believe that adults need less sleep as they get older. But there is no evidence to show that older people can get by with less sleep than younger people. As people age, however, they often get less sleep or they tend to spend less time in the deep, restful stages of sleep. Older people are also more easily awakened.

Does it really matter if you get enough sleep? Absolutely! Not only does the quantity of your sleep matter, but the quality of your sleep is important as well. People whose sleep is interrupted a lot or is cut short might not get enough of certain stages of sleep. In other words, how well rested you are and how well you function the next day depend on your total sleep time and how much of the various stages of sleep you get each night.

Performance: We need sleep to think clearly, react quickly, and create memories. In fact, the pathways in the brain that help us learn and remember are very active when we sleep. Studies show that people who are taught mentally challenging tasks do better after a good night's sleep. Other research suggests that sleep is needed for creative problem solving.

Skimping on sleep has a price. Cutting back by even 1 hour can make it tough to focus the next day and can slow your response time. Studies also find that when you lack sleep, you are more likely to make bad decisions and take more risks. This can result in lower performance on the job or in school and a greater risk for a car crash.

Mood: Sleep also affects mood. Insufficient sleep can make you irritable and is linked to poor behavior and trouble with relationships, especially among children and teens. People who chronically lack sleep are also more likely to become depressed.

Health: Sleep is also important for good health. Studies show that not getting enough sleep or getting poor quality sleep on a regular basis increases the risk of having high blood pressure, heart disease, and other medical conditions.

In addition, during sleep, your body produces valuable hormones. Deep sleep triggers more release of growth hormone, which fuels growth in children, and helps build muscle mass and repair cells and tissues in children and adults. Another type of hormone that increases during sleep works to fight various infections. This might explain why a good night's sleep helps keep you from getting sick-and helps you recover when you do get sick.

Hormones released during sleep also affect how the body uses energy. Studies find that the less people sleep, the more likely they are to be overweight or obese, to develop diabetes, and to prefer eating foods that are high in calories and carbohydrates.

How sleepy you are depends largely on how well you've been sleeping and how much sleep you've been getting. Another key factor is your internal "biological clock"—a tiny bundle of cells in your brain that responds to light signals through your eyes and promotes wakefulness. Because of the timing of the biological clock and other bodily processes, you naturally feel drowsy between midnight and 7 a.m. and again in the midafternoon between 1 p.m. and 4 p.m.

Night shift workers often find themselves drowsy at work. They also have trouble falling asleep or staying asleep during the day, when their schedules require them to sleep. Being sleepy puts them at risk for injuries on the road and at work. Night shift workers are also more likely to have conditions such as heart disease, digestive disorders, and infertility, as well as emotional problems. All of these problems may be related, at least in part, to their chronic lack of sleep.

Adapting to new sleep and wake times can also be hard for travelers crossing time zones, resulting in what's known as jet lag. Jet lag can lead to daytime sleepiness, trouble falling asleep or staying asleep at night, poor concentration, and irritability.

The good news is that by using appropriately timed cues, most people can change their biological clock, but only by 1-2 hours per day at best. Therefore, it can take several days to adjust to a new time zone (or different work schedule). If you'll be moving across time zones, you might want to begin adapting to the new time zone a few days before leaving. Or, if you are traveling for just a few days, you might want to stick with your original sleep schedule and not try to adjust to the new time zone.

Like eating well and being physically active, getting a good night's sleep is vital to your well-being. Here are 13 tips to help you:

• Stick to a sleep schedule. Go to bed and wake up at the same time each day-even on the weekends.
• Exercise is great but not too late in the day. Avoid exercising closer than 5 or 6 hours before bedtime.
• Avoid caffeine and nicotine. The stimulating effects of caffeine in coffee, colas, teas, and chocolate can take as long as 8 hours to wear off fully. Nicotine is also a stimulant.
• Avoid alcoholic drinks before bed. A "nightcap" might help you get to sleep, but alcohol keeps you in the lighter stages of sleep. You also tend to wake up in the middle of the night when the sedating effects have worn off.
• Avoid large meals and beverages late at night. A large meal can cause indigestion that interferes with sleep. Drinking too many fluids at night can cause you to awaken frequently to urinate.
• Avoid medicines that delay or disrupt your sleep, if possible. Some commonly prescribed heart, blood pressure, or asthma medications, as well as some over-the-counter and herbal remedies for coughs, colds, or allergies, can disrupt sleep patterns.
• Don't take naps after 3 p.m. Naps can boost your brain power, but late afternoon naps can make it harder to fall asleep at night. Also, keep naps to under an hour.
• Relax before bed. Take time to unwind. A relaxing activity, such as reading or listening to music, should be part of your bedtime ritual.
• Take a hot bath before bed. The drop in body temperature after the bath may help you feel sleepy, and the bath can help relax you.
• Have a good sleeping environment. Get rid of anything that might distract you from sleep, such as noises, bright lights, an uncomfortable bed, or a TV or computer in the bedroom. Also, keeping the temperature in your bedroom on the cool side can help you sleep better.
• Have the right sunlight exposure. Daylight is key to regulating daily sleep patterns. Try to get outside in natural sunlight for at least 30 minutes each day.
• Don't lie in bed awake. If you find yourself still awake after staying in bed for more than 20 minutes, get up and do some relaxing activity until you feel sleepy. The anxiety of not being able to sleep can make it harder to fall asleep.
• See a doctor if you continue to have trouble sleeping. If you consistently find yourself feeling tired or not well rested during the day despite spending enough time in bed at night, you may have a sleep disorder. Your family doctor or a sleep specialist should be able to help you.