We all do it. Most of us pretty regularly. Three-toed sloths do it for the majority of their existence. Infants do it for nearly 14 hours a day (well for those lucky parents they do), yet the older we get the less sleep we seem to get. At a cost it seems.
But why do we do it?
We know the physiological reasons for why we need to eat, why we need to drink and why we need to breathe.
Yet no one really knows why humans and animals need to sleep – scientists have approached this conundrum from several different angles resulting in many hypotheses and theories – yet none of them provide us with any conclusive evidence as to why the body needs to sleep.
Seeing our nervous system subconsciously regulates sleep in the same way it regulates digestion, heartbeat, breathing, it makes sense to start there.
Cleansing and Restructuring our Brains
One interesting theory is that our brains get rewired whilst we slumber. Research has been performed utilising MRI and PET scans (two imaging techniques which can map out the brain- highlighting areas of activity) on sleeping animals and humans and the findings reveal a link between increased brain plasticity (the term used for the rewiring or re-organising of the brain) and the amount of time spent in a stage of sleep known as REM or rapid eye movement (so called because the eyes appear to move under the eye lids). REM is also that stage of sleep where most dreams occur.
Both animal and human models have also shown that sleep is significant in learning, memory acquisition and retention. The more we sleep the better we learn and the more easily we can recall newly learnt information, it appears.
Survival of Species
Another theory put forward by evolutionary biologists called the “adaptive theory” suggests that the reason for the existence of sleep has to do with the survival of species in the grand scheme (evolutionary biologists somehow always end up at species survival – in any argument really). According to these guys, the reason why we sleep is to take us out of activity at a dangerous time of the “day” – namely the night. At night time we are at our most vulnerable as we can’t see anything and would be easy prey for any predator with better night vision than us (or a keener sense of smell).
But the problem with this theory is that it is slightly illogical – as we are a lot more capable of countering any attack by a would-be predator if we are actually conscious of our surroundings (as in, not sleeping) so we can run, jump, hide… flee basically. So that theory falls flat.
The Body’s Repair Shop
Another theory postulated for why we sleep is based on the ancient belief that sleep in some way serves to restore what we have lost or used up in the body while we were awake. Most ancient cultures believed that sleep was the time we interacted with the gods (or demons) who then either heal us or make us sicker – depending on how nice we were during the day (I guess?). In a more modern interpretation, sleep appears to give our bodies the chance to rejuvenate and repair themselves.
This theory seems to be the one with the most scientific backing, having numerous empirical studies in both humans and animals confirming this idea. Findings show that all the important repair/restorative functions in our bodies such as hormonal release, tissue repair, muscle growth, protein synthesis occur when we are sleeping (in some cases only when we are sleeping).
One slightly disturbing, yet revealing, animal study showed that when monkeys were deprived entirely of sleep, their immune systems stopped working and most died in under 3 weeks. So there is definitely something to the whole rejuvenating and repair argument. The longest any human being has ever stayed awake is around 10-11 days – but don't try this at home!
Sleeping Slows our Metabolism Down
It has been scientifically proven that our metabolism slows down considerably when we are asleep, often by up to 10% (in some species of animal this figure doubles, most notably the three toed sloths). The energy demand of the body slows down as well as the body’s core temperature (an obvious indication that less of everything is going on in the body). So this slowing down of the metabolism and conserving energy theory actually relates a lot to the previous body repair shop analogy.
All in all it seems a combination of all of the above theories is probably the closest thing we have to a universal truth.
The Actual Mechanics of Sleep
The process of falling asleep and waking up is controlled by circadian rhythms also known as internal alarm clocks that oscillate over 24 hours and dictate the behavioural cycle of any living being on the planet. No one really knows what drives this process or ‘who’ or ‘what’ controls it (maybe that’s what god is?). The rhythm is controlled by various zeitgebers (an anglicised German word that literally translates to as much as “time givers” but actually means “time indicators”). In humans the circadian rhythm results in the increase and decrease of various neurotransmitters and hormones. These are in part triggered by sunlight and lack of sunlight.
Most notably, the release of melatonin by the pineal gland (though melatonin is also secreted in smaller amounts in the eye and in the small intestine) is triggered by the sun going down – research has shown that melatonin is almost undetectable in us during the day. Conversely, cortisol – our stress (or ‘fight or flight’) hormone, is triggered by daylight.
Cortisol makes us more alert. Precisely the reason why we are not very reactive once awoken from slumber in the middle of the night– no cortisol equals less responsiveness.
Research is showing that melatonin (as found in tart cherry, as phytomelatonin) is actually more than just a trigger for sleep – recent clinical studies have discovered that melatonin actually has more antioxidant power than Vitamin E (by nearly 200%!) and that it is more effective than even Vitamin C in terms of reducing injury to cells from oxidative stress.
As such it probably makes sense to supplement with it when we are feeling stressed and ill, not only when suffering bouts of insomnia. Also, melatonin production reduces with age and supplementation with it has been shown to tentatively slow down the signs of aging and some daring scientists even proffer, age itself.
Why we really Sleep
I think the real reason we feel the need to sleep at night is an amalgamation of all of the above theories, but one aspect I forgot to touch upon was that in sleeping, we encounter dreams. Dreams are important because they allow us insight into our subconscious and what is really happening to our body on a spiritual level. Morpheus the Greek god of dreams was allegedly said to have sent out messages to his believers in their dreams. And that if you didn’t pay attention to the particular dream message, he would send you a nightmare to “shake you up”. Not to get too esoteric, but maybe there is some truth to the age old knowledge of ancient cultures whose wisdom and insight into the human condition and its place in the world have been largely lost to modern thought and post-modern empiricism.
Dreams give us insight into what is possible.
Not ancient, but definitely a wise culture, the Native Americans believed that the night air was filled with dreams that are both good and bad. Due to this fact, they employed dreamcatchers for when they slept – made out of bits and pieces of everyday life (like arrow heads, bird feathers, stones anything really) the purpose of a dreamcatcher was to allow good dreams into the home and to catch and eliminate bad dreams. The idea was that bad dreams would get confused by all the bits and pieces in the eye of the catcher and get tangled up and remain there until the sun came out the next day and made them go away.
We all need sleep and we all need good dreams. So if you or your kids have been having bad dreams lately or not sleeping well, go out and build a dreamcatcher today!
Hey, you never know until you try, right?
Happy sleeping, people!
by Christopher von Roy BSc, MSc, DCP Immunology
Siegel JM. 2005. Clues to the functions of mammalian sleep. Nature. 437:1264-1271.
Porkka-Heiskanen T. 1999. Adenosine in sleep and wakefulness. Annals of Medicine. 31:125-129.
Frank MG. 2006. The mystery of sleep function: current perspectives and future directions. Reviews in the Neurosciences. 17:375-392.
Pierpaoli W, Regelson W. Pineal control of aging: effect of melatonin and pineal grafting on aging mice. Proc Natl Acad Sci U S A. 1994 Jan 18;91(2):787-91.
Rodella LF, Favero G, Rossini C, et al. Aging and vascular dysfunction: beneficial melatonin effects. Age. 2011 Nov 23. Epub ahead of print.
Wang X. The antiapoptotic activity of melatonin in neurodegenerative diseases. CNS Neurosci Ther. 2009 Winter;15(4):345-57. Review.
Cardinali DP, Pagano ES, Scacchi Bernasconi PA, Reynoso R, Scacchi P. Melatonin and mitochondrial dysfunction in the central nervous system. Horm Behav. 2012 Feb 25.
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