A new school year is about to start, and we all know how sleep-deprived students can be. Parents and teachers may sound like broken records, but Dr. Rosalind Cartwright can tell you that good sleeping habits are nothing to roll your eyes at. Cartwright has dedicated her life’s work to the study of sleep, and in her new book The Twenty-four Hour Mind: The Role of Sleep and Dreaming in Our Emotional Lives she proposes a new theory on the confluence of our dreaming and waking selves. Over the past few months she has been kind enough to discuss the film Inception to how to get rid of nightmares with us. Here Cartwright answers a few more questions I had, like, can we really wean ourselves off sleep? And help, I’m a binge sleeper! –Michelle Rafferty, Publicity
1.) I heard that the amount of sleep we need depends on the person, is this true?
The amount of sleep that is normal for any one person is like asking about the amount of intelligence or height. When we measure a group of the same age and gender, we find most people group around a mid point with a few people at each extreme. That is known as the normal curve. For sleep that mid point is between 7 and 8.5 hours. Short sleepers have less on a regular basis and long sleepers more.
But like height and intelligence, these numbers can be affected by life circumstances (good or bad diet can stunt or increase height, and good or bad education can impact measured intelligence). If you are sleeping under dangerous conditions you will sleep less and more lightly, “with one ear open.” The safer we are the better we sleep. But, the danger for us is more often internal than external; worry is our worst sleep enemy.
2.) I have friends who claim to have “weaned themselves off of sleep,” mostly so that they can cram everything they need to do into one extended day. Can we actually shorten the amount of sleep we need?
Studies in which couples have been motivated to reduce their sleep time were put on a schedule of slowly reducing their time by just 15 minutes a week. The results were that 8 hour sleepers could get down to 6 hours over two months without any loss of attention and learning ability. But once out of the study on their own, they slipped back to being 7 hour sleepers. So that proved that sleep can be shortened some, but not abruptly, and not by much.
And we know that drastic reductions down to 4 hours in healthy young volunteers for only six nights showed a markedly slower rate of glucose clearance. That is an early warning for diabetes. The other scary finding for health is the relation of short sleep and obesity. Short sleep reduces leptin, a hormone that suppresses appetite. With short sleep we wake up hungrier. Those with the best weight to height ratio averaged 7.7 hours of sleep. Those who were most overweight averaged 6 hours or less or 9 hours or more. Cutting down on sleep has real health consequences.
Your friends who tell you they only sleep 4 hours may not tell you about their unintended naps, or their make-up sleep bashes on the weekends. Nor do they report their morning grouchy morning mood and difficulty learning new things or remembering what they already learned.
3.) So people could probably be smarter and happier if they didn’t skip out on sleep?
The sleeping mind keeps working at saving our efforts to learn something new: Spanish or other language, a speech or part in a play, a new golf stroke, etc. If we care about it, emotional value facilitates the preservation of new learning during sleep.
Our emotional health is also greatly influenced by our sleep. Dreams work to down regulate negative mood over night in people who are going through some moderately bad periods. For example, if you go to sleep unsure of how to get out of a bad situation, and are feeling alone and helpless, you might have a dream sequence that looks like this:
First you have a dream in which you are on a roof with no way to get down safely.
The second dream will also be scary, but the story is more developed. You are with a group of people all going on a holiday, but suddenly they are all gone and you are alone in unfamiliar territory and don’t know how to find them.
The next dream you are on stage in a play but you don’t know what part you are supposed to be playing. The audience is waiting, so you bow and leave the stage where a stage manager hands you the script. You glance at it and see that you do in fact know your part. You go back on stage, deliver the last lines, and feel great.
This sequence goes from being stranded without help, to being let down in the middle of a situation that is supposed to be a good time, to again feeling unprepared but manage to get a little help and pulling it off—because you were prepared after all. That’s why “sleeping on it” is good advice.
4.) What if we can’t logistically get all of our sleep in one night. Can we break it up into shifts and still get these benefits?
The Navy has tried this over the years. And we have many studies that have tested out different sleep schedules. Yes, sleep total amount night plus naps can work as well but a good deal depends on the timing of the naps. If you take a late morning nap after a short night you are likely to get mostly REM (rapid eye movement) sleep—or dreaming sleep. If you nap after work you are likely to get more SWS (slow-wave sleep). That is the nap that leaves you groggy because it is like starting your normal night with deep sleep but you feel like you want more rather than refreshed. So mid day or early afternoon naps work best if you keep them short to 20-30 minutes.
5.) What about “binge sleeping”?
Suppose you can’t catch up with longer sleep until the weekends. Most people shift their schedule on the weekends—they to go to bed later and get up later Friday night and Saturday. The problem is Sunday night “insomnia” because the body now expects to go to sleep later. Our internal clock likes to move forward not back. If you are willing to suffer some Sunday night insomnia, the longer sleep (if the youngsters in the house or pets let you) on the weekends can help make up for the “damage” potentially done when you missed sleep earlier in the week.