Eight Hours: Myth or Reality?

By Michael Breus, PhD, ABSM and Stuart J. Meyers, MD
Thursday, 30th August 2007

How much sleep so you really need?

If the sleep fits -

Although many factors influence how much sleep you really need most young adults report sleeping about seven and a half hours on weekday nights and eight and a half hours on weekend nights. And the common recommendation is eight hours a night. But individual needs vary greatly.

There are so-called short-sleepers and long-sleepers -- those who need as little as five and a half hours to as much as about nine and a half hours.

How much sleep you require depends on several factors including:



Your inherited genetic need
Your sleep hygiene (those daily activities you control, from drinking coffee or
alcohol to smoking and exercise)
The quality of your sleep
Your 24-hour daily cycle known as the circadian rhythm

For example, smoking, drinking, and exercise can affect your sleep dramatically. What you actually do in bed (like reading or watching TV) and how much exposure to light you have (looking at that bright computer screen ‘til midnight) will also significantly alter both the quality and quantity of your sleep. They all interact to determine how long you need to sleep to wake up feeling refreshed and remain alert throughout the day.

How did we get the age-old recommendation that we need a solid eight hours of sleep? In a classic study, researchers placed a volunteer in windowless, light-controlled room for 30 days. The light was on for 16 hours and off for eight hours, but the study participant could also turn the lights on and off at will.

Before the experiment began, the subject routinely got about six and a half hours of sleep. During the first night of the experiment he slept eight hours, the second night 10 hours, the third night 12 hours, and the fourth night 14 hours. Over the next several days, he began to reduce the number of hours slept, eventually falling to a steady eight hours and 13 minutes.

This experiment was performed repeatedly with all types of people, with similar results, and this is where the recommendation of eight hours comes from.

Your Sleep Debt

OK, so how do you determine how much sleep you really need?

First, let's look at your bank account -- your sleep bank account, that is -- and see if you have a debt to pay. Throughout the day, you take out about eight hours from this account, generating a sleep debt. Over the course of the night, as you snooze, you replenish your account. If you sleep only, say, six and a half hours, you still owe one and a half hours. If you do this for five nights in a row, you have lost an entire night's sleep! You will then need extra sleep over the next few days to replenish your sleep debt.

How much sleep do you get -- do you have a sleep debt? Do this simple test: Starting on a Sunday, do not drink alcohol or caffeine; do not smoke; go to sleep about the same time every night; and get an uninterrupted seven to eight hours of sleep for the next six nights. Then, on Saturday morning, sleep in. See how long your body will let you sleep.

If you sleep longer than you did during the week -- then you have a sleep debt. So you should consider getting more sleep each night to replenish that sleep debt. Hey, not so easy, you say. Well, give it a try and do the best you can. Why?

Not getting the proper amount of and the best quality sleep may have serious consequences. Many studies have shown that sleep deprivation adversely affects performance and alertness. Reducing sleep by as little as one and a half hours for just one night reduces daytime alertness by about one-third. Excessive daytime sleepiness impairs memory and the ability to think and process information, and contributes to a substantially increased risk of sustaining an occupational injury.

The bottom line is that you should wake up feeling relatively refreshed, and you should generally not feel sleepy during the day. If this is not the case, you may have an unrecognized sleep disorder and should see your doctor or a sleep specialist.

Medically Updated: July, 2006

SOURCES: Sleep Medicine, Kryger, Meir, et al., Third Edition, 2000. Sleep: "Excessive Daytime Sleepiness and risk of Occupational Injuries in Non-shift Daytime Workers," Vol. no. 3. Sleep: "Dose-response Relationship Between Sleep Duration and Human Psychomotor Vigilance and Subjective Awareness," Vol. 22, No. 2. Sleep: "We Are Chronically Sleep Deprived," Vol. 18 No. 10. The Promise of Sleep, by William Dement.

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