The average american will sleep 6.8hrs per night, out of a 24hr day this means we’re spending around 28% of our lives deep in the comforting embrace of unconsciousness. To the ambitious this might seem like a waste of precious time but as we’ll discover the quality and quantity of time spent between the sheets may be some of most crucial hours of our day when it comes to determining the quality of our waking life and health outcomes.
So what is sleep?
It seems obvious, but most of us have only a vague notion of what we’re truly undergoing when we hit the sack. Through a scientific lens sleep can be characterized as a state of unconsciousness that is relatively easy to reverse (compared to coma or hibernation), in this state we can observe a series of predictable neurological and physiological changes depending on which phase of sleep we are in.
There are currently thought to be 4 phases of sleep, these include Non-Rapid Eye Movement(NREM) which consists of three phases N-1, N-2, N-3 and REM (rapid eye movement). In a healthy night sleep we undergo all phases in cycles lasting 90–110 minutes. As the night progresses our REM phase of sleep often associated with dreams become lengthened resulting in more vivid dreams.
NREM N-1 (Light Sleep)
Initially we nod off from our wakeful alpha brain waves into our first NREM N-1 phase which typically only lasts around 10 minutes. N-1 is our lightest phase of sleep and can be identified as the stage of sleep where we occasionally experience falling sensations followed by jerking awake, a phenomenon known as hypnic jerk or sleep starts.
NREM N-2 (Light Sleep)
Once we’ve passed from our initial light N-1 phase we begin to enter N-2, the first proper state of NREM sleep where physiological markers such as decreased heart rate and body temperature begin to be observed. Being woken by external stimuli is less likely in N-2 than N-1. Studies report that N-2 is the longest sleep phase we experience, contributing 50% of our total sleep time.
NREM N-3 (Slow Wave Sleep)
Lasting approximately 45–90 minutes per cycle, N-3 represents the deepest and most restorative phase of sleep. We can observe our heart rate, blood pressure and body temperature all decrease significantly during this phase as our brains begin to produce slow delta-waves. This phase of sleep is often attributed to cerebral regeneration along with other auspicious biological processes such as human growth hormone secretion, immune system regulation and long term memory consolidation. The recovery we receive from this deep sleep could be attributed to the notable decrease in Sympathetic nervous system (responsible for regulating our fight-or-fight response) activity and increase in parasympathetic nervous system activity.
REM (Rapid Eye Movement)
REM Sleep is synonymous as the phase of sleep in which we experience our dreaming state, although the hard science behind why we dream is still a mystery we can observe various tell tale signs of REM sleep. Physiologically we see an increase in Brain activity (most likely associated with dreaming) alongside erratic peaks and troughs of heart rate, respiration and body temperature at the same time we experience temporary paralysis of muscles most likely to ensure dreams are not physically enacted.
Why do we need sleep?
From just a quick peak under the hood of a typical nights sleep we can see that slumber isn’t as much of an inactive process as we would have once thought. There are still many unanswered questions regarding the necessity of sleep and the mechanisms behind it’s support to overall physiological functioning, perhaps an easier way to gain a more fundamental understanding of sleep’s importance is looking at the correlations between health outcomes and sleep patterns.
Studies has reported an association between a lack of sleep and worsened blood pressure and cholesterol, two major risk factors contributing to heart attacks and strokes. During NREM sleep we also experience a decrease in heart rate which has been hypothesized as a chance to give our cardiovascular system a chance to rest and recover.
Researches believe melatonin, the hormone responsible for regulating our sleep-wake cycle, may in fact act as a powerful agent to suppress the growth of tumors and cancerous cells. By increasing our sleep quantity and reducing blue-light exposure prior to sleep we can improve and support melatonin production thereby decreasing risk of cancerous cell growth.
Two hormones that regulate our appetite known as grhelin (increases appetite) and leptin (decreases appetite) are modulated in sequence to our sleep-wake cycle. When we sleep leptin increases whilst grhelin decreases to signal that we have enough calories to sustain ourselves and suppress sensations of hunger. When we experience extended periods of sleep disturbance leptin levels decrease and grhelin increases resulting in over-eating and weight gain.
Enhance Learning & Cognition
NREM sleep plays a critical role in the consolidation of memory. In our waking life our brains are continuously processing information at a rapid rate, sleep provides us with the much needed opportunity to consolidate and integrate this information into long term memory. REM sleep on the other hand has been shown to increase creativity and our ability to draw associations from two distant subjects.
Reduce Stress & Recovery
A down-regulation of our Sympathetic Nervous System and secretion of human growth hormone provides lowered levels of stress hormone cortisol, resulting in a greater ability for tissue recovery than we would find in our waking state. This increase in human growth hormone also plays a vital role in muscle tissue synthesis & restoration making sleep essential for athletes.
The Takeaway & Prescription
From cognitive to physical performance and recovery, optimizing the biological process-rich act of sleep should be of paramount importance to anyone looking at squeezing out the most of their day. The amount of sleep required to hit healthy levels will vary from individual to individual depending on age and overall quality of sleep, as a rule of thumb aim for no less than 7–9hrs per night.
Stay tuned for our next article where we take a deep dive into the top 5 methods of optimizing your sleep cycle.