Wednesday, 27 October 2010

Somewhere in Night Time

We often think of a good night's sleep as something along the lines of eight hours of uninterrupted snoozing.  Kind of like 'lights out' when your head hits the pillow, not stirring until the next morning.  I disagree.

In an exchange with Methuselah some time ago, we ruminated on actually how 'normal' it is to be 'zonked out' for eight hours solid.  From a hunter's perspective what could be more appealing than your prey snoozing away in a deep sleep?  Hunting would become tame to say the least, and your prey's appearance on the tree of life would be likely VERY short.

These thoughts bubbled up when I was trying hard to sleep more.  I had read 'Lights Out' and was reflecting on Wiley and Formby's claim that short nights 'mimic summer' and so lead to:
  • reduced melatonin secretion, which reduces white cell immune function;
  • a severe reduction in the most potent antioxidant you have - melatonin;
  • less prolactin at night and way too much in the daytime (prolactin secretion at night means more and stronger NK and T cells.  Prolactin secretion during the day means autoimmunity and carbohydrate craving).
Melatonin cannot be made in daytime or with lights on.  In addition, they observe that,
  • ...the biggest problem with short nights year-round, beyond appetite derangement, is that insulin will stay higher during the dark, when it should be flat, and cortisol falls so late it won't come up normally in the morning.  This is a reversal of normal hormonal rhythms.  You should wake up with elevated cortisol to deal with stress during the day.  You should wake up hungry with low insulin and cortisol rising.  Instead your cortisol is low and your insulin is up."
(Now I figured that high insulin would make you hungry....).  But anyway, by messing with our light-adapted hormonal responses we end up with high prolactin in the morning which makes us kind of dozy, and the elevated prolactin also suppresses leptin so you can get hungry late afternoon. 

Hunger should be your alarm clock,
  • One of the evolutionary functions of melatonin is that it enhances the appetite-suppressing effect of leptin so you stay asleep instead of roaming around hungry all night.  It's a feedback loop:  Melatonin enhances leptin and leptin keeps your brain in the "fed" stage, so you stay asleep and make more melatonin.
I think I have just about got my head around all that!  There are good hormonal reasons why we should sleep in the day and night cycles we do.

Captain Kid and Flash are currently exhibiting a significant fear of the dark at the moment (not the album by Iron Maiden, the physical drawing-in of the nights).  I can see why it would make sense that 'evolution' has removed those of our kin who wandered off at night in the dim and distant past.  I see fear of the dark, as evolutionarily advantageous.  With our poor night sight, inferior hearing and poor sense of smell, we NEED light to ensure our survival on a physical level.

So pondering all this 'why we sleep at night' stuff, it got me thinking about the nature of sleep itself.  Why, when I went to bed earlier, did I keep waking through the night - was this a good or a bad thing?  I was waking up refreshed the next morning,  but my idea about sleep was that is should be continuous.  I had an idea that wakefulness meant my sleep was disturbed and so might he detrimental to 'hormonal release'.  From an evolutionary perspective though, continuous sleep did not seem like a successful strategy but I was mindful that optimal hormone secretion was closely tied to 'a good night's sleep'.

It seems much more intuitive that our sleep pattern should ebb and flow with periods of mild wakefulness and periods of much deeper (and therefore more vulnerable) phases of sleep.  If this pattern is random, then amongst a small group or tribe - there should seldom if ever be a point where everyone in the tribe is vulnerable; or rather there should always be someone who is either awake or sleeping lightly enough to be stirred should something hazardous approach.

This very theme is touched upon in Catching Fire by Richard Wrangham.  In it, Wrangham notes how our long legs and flat feet make us poorly adapted to climbing in trees and building nests like the great apes.  A mother with child would find this doubly difficult.  We must have slept on the ground.  But given our inferior night-senses, our limited sprinting ability and dependence on weapons for defense, there must have been another X factor (not the Iron Maiden album, nor the TV program).  This X factor was fire which allowed us to sleep safely on the ground and which we have been using for perhaps the last 400,000 years,
  • "If homo-erectus used fire...[he] could sleep in the same way as people do nowadays in the savanna.  In the bush, people like close to the fire and for most or all of the night, someone is awake.  When a sleeper awakens, he or she might poke at the fire and chat a while, allowing another to fall asleep.  In a twelve-hour night with no light other than what the fire provides, there is no need to have a continuous eight-hour sleep.  An informal system of guarding easily emerges that allows enough hours of sleep for all while ensuring the presence of an alert sentinel.  To judge from records of attacks by jaguars, modern hunter-gatherers are safer in camp at night than they are on the hunt by day"
So it looks like as long as you awake refreshed in the morning, as long as your night isn't 'restless', stirring throughout the night is fine and indicative of optimal sleep and rest.  Sleeping with some light may also be fine - as long as it is of the right frequency  - towards the red end of the spectrum. 

In fact for the past few years I have made Mrs A use a red bike light to go to the bathroom rather than turning on the main light in the en-suite as the latter is blue/white in colour.  (I should add that this strategy is heavily resisted my Mrs A).  There are some concerns about the use of LED lights, but these seem to be limited to blue frequencies.

For me I usually try to head to bed soon after 2100hrs (not always a successful strategy) with an aim of resting/sleeping until 0700hrs.  My bedroom is very dark and minimalistic.  I read a book which naturally allows me to 'wind down'.  And when/if I do wake through the night, I simply cast a quick eye around my 'camp' to make sure my 'tribe' is safe.

UPDATE:
Chris has just sent me a great link to an article about a book exploring our relationship with artificial light,
  • "The most arresting example of this complex relationship is the effect that artificial light has had on our natural sleep cycle. Brox cites historians and sleep scientists to explain that when no artificial light is present humans experience what is called “divided sleep”, which is a period of intense sleep followed by a period of wakefulness in the middle of the night during which you would be awake and active. This is then followed by a “second sleep” which is a lighter, dream filled state which lasts until morning. People on long hiking trips can begin to experience this after a week of being in the wilderness. Artificial light has changed the most basic way that we live."

1 comment:

Methuselah said...

I am definately of the opinion that broken sleep is a part of a normal healthy existence. The healthier and more balanced I am, the more broken my sleep - yet during the day I feel great. When my sleep is heavy and unbroken (e.g. due to excess food and drink and general bad living and/or jet lag) I nevertheless feel lousy during the day. Having just combined all three in the last week I can speka from recent experience!