Sleep
I've become a bit addicted to my Whoop. Every morning after I wake I quickly open the Whoop app on my phone to process my nights sleep and see how it interprets my data - my sleep quality and recovery. It gives me information in terms of time in bed, number of disturbances, sleep efficiency, my respiratory rate and a breakdown of my sleep stages.
It is the sleep stages part that I used not understand - I have heard about REM and deep sleep and light sleep, but what do they indicate, how much of each type of sleep should I actually be getting. Should I care?
It turns out that humans cycle between two completely different types of sleep. They are named based on their effect on eye-movements - NREM (non-rapid eye movement) sleep and REM (rapid eye movement) sleep. These two stages of sleep play out in a recurring battle for brain domination throughout the night. The battle occurs in generally 90 minute cycles starting with NREM and then REM. However, it is not a repeating cycle as the amount of each type of sleep varies as the night goes on. Early on the vast majority of our sleep cycle is dominated by NREM but as the night continues REM dominates with little NREM sleep. This is really important, as let's say you go asleep at midnight and with an intended 8 hour sleep you should wake at 8am. Suppose though you get up at 6am to go the gym. Whilst you lose 25% of your sleep requirement, you proportionately lose out on a lot more REM sleep than NREM as REM is backloaded in your sleep cycles.
NREM is your deep sleep. In fact, there are 4 stages to NREM sleep, imaginatively called stages 1,2,3 and 4! Stages 3 and 4 are the deepest stages, sometimes called SWS (slow wave sleep), with depth relating to the increasing difficulty required to wake an individual. The hypnogram below gives an overview of the architecture of a nights sleep:
A key function of NREM, which dominates your early sleep, is to do the work of weeding out and removing unnecessary neural connections - it is doing neural housework. It is also vital for memory consolidation. In a prior blog on Hangxiety I mentioned how alcohol impacts your sleep and if it impacts NREM, then that contributes to you perhaps not remembering exactly what happened the night before! NREM is also associated with physical recovery, immune system energizing and blood-sugar rebalancing. You don't generally dream during NREM, at least in the lighter stages, and your muscles are free to move - if you are prone to sleepwalking it is likely to be in an NREM phase and hence early on in your nights sleep. NREM sleep tends to be more calm and is parasympathetic (if you read my previous blog on HRV you might remember that a parasympathetic activity lowers heart rate). How much NREM do you need, well it depends on the individual, and your age. As you get older you tend to need less deep sleep - NREM stages 3 and 4. In general though, NREM constitutes 75-80% of total time spent in sleep with REM making up the remaining 20-25%.
REM then occurs in each sleep cycle but is greater in the later cycles. REM is very different to NREM. For a start, your muscles are generally in paralysis, you can't move. This might be just as well, as it is in this phase that you dream. The paralysis stops you acting out your dreams! REM fulfils important physiological needs for survival, to the extent that prolonged REM sleep deprivation can lead to death. REM again plays an important role in memory, learning and thinking - deciding to 'sleep on it' actually is an event in your REM processes. Your brain is highly active during REM, almost the same as being awake, and your body is undertaking more sympathetic activities resulting in heart-rate, breathing rate increases and twitching.
In Matthew Walker's book, 'Why We Sleep', the author calls out a number of significant benefits to getting quality sleep:
You live longer
Sleep enhances your memory and makes you more creative
It makes you look more attractive
Sleep helps lower food cravings and keeps you slim
It protects you from cancer and dementia
Sleep helps ward off colds and flus and other viruses
It lowers the risk of heart attack, stroke and diabetes
Sleep can make you feel happier and less anxious
If you could manufacture a pill that offered some of the above you would be rich and lauded as a medical genius and yet the answer is in all of our own hands.
