Sunday 12 June 2011

Sleep and diversity

In an interesting article on sleep in traditional societies on Science News (which is not the news section of Science), Bruce Bower states that people used to sleep in groups and that differences in sleeping time where an advantage as it provided better protection for the sleeping group.
... sleep typically unfolds in shared spaces that feature constant background noise emanating from other sleepers, various domestic animals, fires maintained for warmth and protection from predators, and other people's nearby nighttime activities.
In traditional settings, however, highly variable sleep schedules among individuals and age groups prove invaluable, since they allow for someone to be awake or easily roused at all times should danger arise, Worthman holds.
Thus a diversity of sleep schedules may be well adaptive, may have been selected for by evolution as it provides better protection. It would be great if modern society would allow people to follow these natural needs, instead of forcing a fixed schedule on early birds and night owls.

By the way, the circadian sleep-wake cycle itself is an example of variability in the activity level. Science still wonders why we sleep. It may well be related to this variability, which allows one to be more active during the day; while at night the reserves are filled again and repairs are performed. A remaining question would still be why you need to close your eyes for this, which is dangerous.

Sleeping without mattress

I found the article linked on the page The Ergonomics of Sleep: Why a Hard Surface can Provide Sweet Dreams. This page argues that sleeping on a mattress is a recent invention and may not be ideal for everyone. To me it makes sense to use traditional behavior as Null-hypothesis; modern ideas are often useful (for instance, hygiene and vaccinations), but should be tested. Thus one week ago, I removed my mattress to see it this works for me and slept on the wooden panel below, but I did add an exercise mat and a comforter (German: Bettdecke) as cushioning. It is definitely not comfortable, but I sleep well, wake up much more alert and it is easy to get out of bed.

What makes it uncomfortable is that your weight is mainly born by your bones. If you sleep on your back your weight is on your heels, pelvis, shoulder blades and skull, on your side it is on your ankle, pelvis and shoulder, on your front the tops of the feet, the knees, pelvis, ribs (man) and collar bones. May there be a reason why exactly these places have no padding, no fat nor muscle? The reduced pressure on the weak body parts could maybe be beneficial for the circulation. Lying in a dimple on a mattress could change your posture (round back) and consequently your breathing.

I am curious what other people experienced and know about this topic; please leave a comment.

Further reading

More posts on paleo (diet and lifestyle topics inspired by evolutionary thinking).

Paleo and fruitarian lifestyles have a lot in common
A comparison of the main ideas and recommendations of these two lifestyles.
Natural cures for asthma?
Some ideas for natural ways, which helped me cure or reduce asthma.
Is obesity bias evolutionary?
A critical comment on an article, which states that humans have an intrinsic propensity to eat too much.
Freedom to learn
Forcing children to learn stifles their innate motivation to teach themselves and may thus be counter productive.
The paleo culture
After the Ancestral Health Symposium 2012, as discussion started about the sometimes self-centred culture of the paleo community


  1. I believe there may be numerous advantages to back sleeping.
    I thought you may find this site interesting:

    This is an Italian oral surgeon who suggests that side sleeping interferes with the natural swallowing that takes place during sleep and this causes bruxism, headaches, neck pain and other issues. Rather than resorting to surgery or expensive mouth guards, he tries to get patients to simply train themselves to sleep on their backs. This alone allows the jaw to relax and the lower jaw to drop down. I have bruxism and was a big side sleeper. With a soft mattress -- side sleeping becomes more "necessary" as the mattress sagging worsens. I found that training myself to sleep on my back -- it can be done despite being a lifelong side sleeper -- but easier with firmer mattress -- has immensely improved my bruxism. I am next going to get rid of the mattress altogether and simply sleep on a matt/wood plank on top of metal frame. I have found that a "hard" buckwheat filled pillow also helps keep me on my back. I simply make a dimple for my head and the firmness of the buckwheat hulls keep my head in position while supporting my neck. I've had neck problems in the past and now realize that the bruxism and neck issues are connected. I think back sleeping is a good strategy for most people. "A in NYC"

    1. Hard to judge the seriousness of that homepage; sounds like the science should still be done. Still, just as with sleeping without a mattress, you can test it for free. Thus even if it does not work, at least you did not get conned.

      Without a mattress you will probably find that you will naturally sleep mostly on your back as this is most comfortable, especially in the beginning.

    2. Dear anonymous, watching myself sleep the last few days, there may well be something to the idea that it is not good to rest on your lower jaw. I noticed that if I sleep on the side, I put one or two hands below my skull or shape my pillow such that my jaw floats in the air.

  2. Hello Victor,
    I linked to your blog from CarbSanity. In re: sleeping well, last year I read the report from a study on sleep done by French and Swiss. The word 'hammock' was used in regards to the movement of what turned out to be a flat mattress. But the 'hammock effect' intrigued me. You'll need to check the study because I can't right now give a link to it.

    I get terrible back muscle pain. When I was youngER (20+ years ago) I could get an absolutely fabulous sleep just on the carpet in my living room. But these days sleeping on a hard surface cripples me. Yes, I do sleep on my back. I've built my own bed with differing amounts of hardness and despite telling myself night after night that millions of people sleep on just such hard surfaces with no problems, I just could no longer adapt.

    The concept of 'hammocks' intrigued me and these things are very cheap. I madly read everything I could find about hammock sleeping. I have wasted much more money in my life and decided that if a hammock was not a good investment, then the money potentially thrown out wasn't going to be significant enough to cause remorse.

    For the past year I have been sleeping in a Mayan hammock. It took a bit of figuring out with tensions, addition of a wool duvet and sometimes a sub-duvet electric heating pad, to come up with what is 100% comfort.

    How do I judge this? I do not wake up multiple times during the night. The only way to explain it is in simple terms because sleep has become so simple: I fall asleep. I wake up in the morning. Between times I may as well be dead. My arms do not go numb during the night. I now frequently have very good dreams as opposed to arduous tiring dreams from which I woke unrefreshed. When I wake up in the morning, I just lie still and enjoy how my body is so comfortable that I am aware of my mind but not my body. I am not stiff or sore when I get up from the hammock. In fact, I move with flexibility.

    A properly hung hammock looks like a banana curve but when a person is lying in it, the body is not curved like a banana. It is relatively flat, the head is elevated and the feet usually find locations where the legs are also flat.

    Getting up from the hammock (in which I 'hang out' when I'm at home) several times during any given 24 hour period has strengthened the muscles supporting my knees. It's like getting up from a squat. (Doing this plus walking down many, many flights of stairs every day has eliminated the pain in my broken right knee for which I had considered having surgery. No more.)

    I place a wool duvet into the hammock, lie in and wrap the duvet around me like a sleeping bag. At first I felt restricted but have adapted the method of covering up and also providing my head with a bit of duvet comfort as well. Mostly I need the duvet so my young cats don't stick their claws into my toes. Even the duvet is no protection from Oscar, who will gnaw on my kneecap through the duvet in the morning if he wants his breakfast. But at least he waits until at least 6 a.m.

    I just thought I'd post this because hammock sleeping is common in many parts of the world and possibly worth considering by some people, who like me, have badly damaged backs which can no longer tolerate hard surfaces most of the time.


    Dr. G. Kadar

    1. Dear Gabriella, thank you for a very interesting comment. I was unable to find anything on sleep and hammocks in the reviewed literature. Thus if you ever find that link again, please give us a hint.

  3. Victor, you should be able to get from the NPR interview to the Current Biology article:

    Please note though that the actual structure of what was used in the study is not a traditional hammock but a mattress that was rocked back and forth.

    I just went one step further by exploring the possibility of getting a better night's sleep.

    As a side note, I injured my left shoulder on Monday. It's probably a rotator cuff tear and these things are notorious for causing pain and preventing restful sleep. I did not realize I'd injured the shoulder immediately after the incident because I was more concerned with having injured my wrist. 48 hours later as per the usual inflammatory response, the shoulder began to ache and certain arm movements are painful and restricted. Last night when I went to 'hammock' I was wondering how much adverse effect the shoulder injury would have on my sleep. I'm happy to report that it did not either prevent me from getting to sleep, nor did it wake me up during the night and when I woke up this morning I was entirely painfree and comfortable as per the usual in the hammock.

    Of course when I attempted to get dressed, the pain intruded. But that can't be helped. I'm hoping that the duration of time to recovery will be shorter than previous rotator cuff tear episodes where I was sleeping on a mattress. Will the fact that the quality of my sleep is not compromised by nocturnal episodes of pain speed recovery? The last time I injured a rotator cuff was 1998 and was unable for approximately 1 year to get a night's sleep without waking up while moving around because the shoulder hurt too much.

    1. Thank you, I will listen to the NPR interview and I found the article.

      For those interested: Rocking synchronizes brain waves during a short nap, Current Biology, Volume 21, Issue 12, R461-R462, 21 June 2011, doi:10.1016/j.cub.2011.05.012.

      Abstract. Why do we cradle babies or irresistibly fall asleep in a hammock? Although such simple behaviors are common across cultures and generations, the nature of the link between rocking and sleep is poorly understood [1,2]. Here we aimed to demonstrate that swinging can modulate physiological parameters of human sleep. To this end, we chose to study sleep during an afternoon nap using polysomnography and EEG spectral analyses. We show that lying on a slowly rocking bed (0.25 Hz) facilitates the transition from waking to sleep, and increases the duration of stage N2 sleep. Rocking also induces a sustained boosting of slow oscillations and spindle activity. It is proposed that sensory stimulation associated with a swinging motion exerts a synchronizing action in the brain that reinforces endogenous sleep rhythms. These results thus provide scientific support to the traditional belief that rocking can soothe our sleep.

    2. Victor, back in 1998 I had a sleep study done due to non-restorative sleep caused by pain. The sleep was fragmented to the point where the respirologist said 'you are out of sleep 60 times per hour. You are not sleeping and that is why you are so tired in the morning.'

      Next time I'm going to my doctor I am going to ask to have another sleep study done and I will inform the centre at which it will be carried out that they will need to remove the bed and let me set up my hammock. After all they want the patient to sleep in the way they do at home, including any sleep aids like medication etc. I am extremely curious to find out how the brain waves are doing now that I sleep like the dead. Aside from whatever effect I'm having from the hammock, I am also interested in any variations in oxygen saturations. Is there any sleep apnea or hypopnea occuring? Because since the hammock keeps the rear end lower than the head, gravity should be on my side with regards to maintaining a lower blood pressure in the head and preventing any oedema in the head and neck. Also, the hammock does not impinge on diagphragmatic function so the breathing should be free and clear in all aspects. For sure I'm not restless although the hammock does permit movement. I fall asleep far over on the right side, not quite on my front but close. At some point after falling asleep I roll over onto my back and based on the lack of messy hair, the sleep is not accompanied by much in the way of restlessness.

      During the first two months I did wake up during the night. My subjective sensation at those times was "I have a mind, it's active but I am not getting any intrusive sensations from possessing a body."


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