By Gregg D. Jacobs, Ph.D.

Waking up later than usual causes what sleep researchers call a phase delay in body temperature. Specifically, the usual rise in body temperature that coincides with arising from bed in the morning, becoming physically active and exposing ourselves to light will be delayed due to sleeping in. As a result, the usual drop in body temperature that precedes the onset of sleep in the evening will also be delayed by several hours. As a result, it will be harder to fall asleep at bedtime.

Secondly, sleeping in after a bad night’s sleep or on the weekend reduces what sleep researchers call prior wakefulness. Prior wakefulness refers to the amount of time that has elapsed from the time you rise in the morning until you turn off the lights at bedtime. Our sleep system follows a basic principle: the greater the amount of prior wakefulness, the greater the brain’s pressure for sleep and the better we sleep.

What is sleep pressure?
Sleep researchers believe that sleep pressure is the result of a sleep-inducing neurotransmitter in the brain called adenosine accumulating with each hour of prior wakefulness. With increasing prior wakefulness, we also increase sleep pressure due to increased cerebral and physical energy expenditure during the day. See Sleep Basics for more information on the physiology of sleep. Since sleeping in reduces prior wakefulness, it reduces sleep pressure and makes it harder to sleep.

Sleep scheduling guideline #1: Get out of bed within a half hour of the same time every day, including weekends, no matter how little or poorly you have slept. The more consistent your wake time, the more consistent your body temperature rhythm and prior wakefulness and the more consistent your sleep.

Another common strategy to cope with insomnia is to spend more and more time in bed in an effort to catch up on lost sleep. This may involve going to bed earlier or staying in bed later, or both. However, spending more time in bed actually increases sleep problems for several reasons. First, increased time in bed reduces prior wakefulness, which disturbs sleep. Secondly, increased time in bed leads to lower sleep efficiency, which makes the bed a stronger cue for wakefulness.

What is sleep efficiency?
Sleep efficiency is the ratio of time asleep divided by time allotted for sleep. So, if you turn the lights off at 11:00 pm and awaken at 7:00 am, your time allotted for sleep is eight hours. If you slept four hours, your sleep efficiency is 50%. This means that your brain associates your bed as much with wakefulness as it does with sleep! The higher your sleep efficiency, the stronger the association between the bed and sleep and the more your bed becomes a cue for sleep. Conversely, the lower your sleep efficiency, the more your bed becomes a cue for wakefulness.

Sleep scheduling guideline #2: Reduce your time allotted for sleep so that it more closely matches the amount of sleep you average each night. This can be accomplished by going to bed later, getting up earlier or a combination of both. You can determine your maximum allowable time in bed by simply adding one hour to your average sleep time. For example, if you average five hours of sleep per night, reduce your time allotted for sleep to six hours. You can also determine your earliest allowable bedtime by starting from your desired arising time (from Guideline #1) and subtracting your maximum allowable time allotted for sleep. Thus, if your maximum allowable time allotted for sleep is six hours and your targeted arising time is 6 am, you should avoid going to bed before midnight.

Reducing time in bed will increase total sleep time by increasing prior wakefulness and the pressure for sleep; it will also improve sleep by making the bed a stronger cue for sleep by increasing sleep efficiency. Reducing time in bed is only temporary until your sleep time and sleep efficiency increases. Once your sleep efficiency reaches about 85% for a week, increase your time allotted for sleep by one half hour per week until your reach your maximum attainable sleep duration.

For additional techniques for improving sleep, see the Truestar Sleep Tips.

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