Friday, November 25, 2011
Our bodies are programmed for two natural periods of sleepiness during a 24-hour day, no matter how much sleep we've had in the previous 24 hours. The primary period is between midnight and 7 a.m., and a second period occurs in the midafternoon, between 1 p.m. and 4 p.m.
Sleep needs vary from person to person, and they change throughout a person’s lifecycle. Children in preschool need 11 to 13 hours of sleep per night. Newborns sleep up to 18 hours a day, and school-aged children (up to age 12) need 10 to 11 hours. Adolescents need about nine hours of sleep a night, and most adults need seven to nine hours of sleep.
Poor sleep is not a normal part of aging. As we get older, we often get less sleep because our ability to sleep for long periods of time and get into the deep restful stages of sleep can decrease. Older people have more fragile sleep and are more easily disturbed by light, noise, and pain. They also may have medical conditions that contribute to sleep problems.
On average, we spend about two hours dreaming each night, or 20% to 25% of a night’s sleep. Some researchers think dreams are merely a byproduct of sleep, but others believe they’re important for mood regulation, problem solving, and stress reduction.
Nightmares, which are dreams that cause high levels of distress or terror, occur more often when you are stressed or anxious. They are more likely to occur in the last third of the night and tend to be more common among children than adults.
Sleepwalking may include simply sitting up and appearing awake, or it may involve complex activities, such as moving furniture, going to the bathroom, eating, or, in rare instances, driving. Sleepwalking occurs more often in children and appears to run in families.
Drowsiness can be as dangerous as driving drunk; research has indicated that it’s comparable to driving with a blood-alcohol level of 0.08, the legal limit for intoxication in many states. The problem is greatest among males aged 16 to 29, people who work irregular shifts, and people with untreated sleep apnea.
If you don’t get the amount of sleep your body needs (typically 7 to 9 hours per night for adults), you start to accumulate a “sleep debt.” You can pay off a debt of a few hours by getting extra sleep over the next week or so, which is why you may have such a strong urge to sleep in on Saturday mornings. However, if the debt remains unresolved and continues to mount, you could be at increased risk for accidents or injury.
In addition to blurred vision, not getting enough sleep can cause fatigue, irritability, and an inability to concentrate. Because these can be symptoms of other conditions as well, it may be helpful to keep a sleep journal and discuss your issues with your doctor.
Several studies have shown that not getting enough sleep or a decrease in sleep quality can affect appetite controls and lead to overeating. Sleep loss has also been tied to decreased insulin sensitivity and increased risk of diabetes.
Poor sleep can contribute to heart disease, and heart disease can interrupt sleep. Poor sleep also has been associated with high blood pressure and stroke. Experts believe that such factors as inflammation and stress play a role. For example, with sleep apnea, pauses in breathing during sleep and low oxygen levels stress the body and promote inflammation.
Chronic insomnia is when a person has difficulty falling asleep or staying asleep at least three nights a week for a month or longer. Acute insomnia can last for a few nights to a few weeks.
Breathing pauses associated with sleep apnea often occur five to 30 times or more per hour and can last from a few seconds to a few minutes, resulting in poor sleep that makes you tired during the day. The most common type of sleep apnea is obstructive sleep apnea, which usually is caused by the airway collapsing or being blocked during sleep.
Common signs of obstructive sleep apnea include loud snoring, morning headaches, irritability, memory and concentration problems, and a dry throat upon waking. Most people with sleep apnea don’t know they have the condition, and it often goes undiagnosed.
The first state of sleep is NREM sleep, and it consists of four stages (light sleep, onset of sleep, and two stages of deep, restorative sleep). During these stages, the muscles of the eyes are relaxed. The second state, REM sleep, is associated with increased contraction of the eye muscles. Both types are necessary for quality sleep.