If you haven’t already read part one of our sleep series, get up to speed here.
Now we have discussed some of the key sleep science and looked at how fixing our sleeping routine is the best thing we can all do for Alzheimer’s prevention, this alone should be a sufficient reason to prioritize your sleep. In case you are unconvinced, fear not; parts two, three, and four will really hammer the message home. Be sure to check out Peter Attia’s podcast trilogy with Matthew Walker and get a copy of Dr. Walker’s International Bestseller, Why We Sleep.
You are what you sleep
Diet, exercise, and sleep are often known as the three pillars of wellbeing. However, Dr Walker suggests that sleep is the foundation on which the other two sit; without sufficient sleep, the benefits of diet and exercise cannot be exploited. The simple fact that sleep scientists have found a 30% decrease in time to physical exhaustion when limited to 6 hours of sleep adequately paints the picture. It has been shown that sleeping well helps you to make better food choices and lower your caloric intake whilst increasing your caloric expenditure. Let’s take a look at the science:
The amount of sleep you get affects the regulation of two hormones called leptin and ghrelin. Leptin tells your brain that you are satiated, whilst ghrelin tells your brain that you are hungry. In other words, ghrelin is the hunger signal. When underslept, leptin levels fall and ghrelin levels rise, which causes you to eat more and make worse food choices. Dr. Walker lays out a simple equation: less sleep equals increased caloric intake and not of the good kind. The average caloric intake roughly equates to 10lbs per year, a figure painfully familiar to many.
Here are three more hormones to add to the list negatively affected by insufficient sleep: testosterone, FSH, and LH. Men who sleep 5-6 hours a night will have a level of testosterone similar to that of someone 10 years their senior. Meanwhile, a reduction in FSH and LH results in fewer sperm and more abnormalities. For women, a reduction in FSH and LH impacts fertility and increases the chance of irregular menstrual cycles.
Want to eat well? Then sleep well. A lack of sleep can also reduce your impulse control. The decision-making prefrontal cortex goes “offline” and lets more primitive areas such as the amygdala call the shots. Moreover, Dr. Walker warns that getting insufficient sleep will derail your diet, whether that be weight loss, gain, or maintenance. If you are sleeping 6 hours or less, then 70% of weight loss will come from lean muscle mass as your body holds on ruthlessly to its fat. It goes without saying that these are not ideal mass building conditions either.
Time for another hormone: insulin. Produced by the pancreas, insulin is the hormone that allows your body to use glucose from carbohydrates for energy or to store for future use. A lack of sleep results in insufficient insulin levels and reduces the body’s ability to identify insulin. There is a correlation between diabetes and untreated sleep apnoea, a chronic condition characterized by momentary pauses in breathing and snoring during sleep. However, once sleep apnea is treated, people’s diabetic profile improves dramatically, and so too do their food choices, energy levels, and physical activity levels. Sleep has a notably positive impact on lifestyle habits across the board.
Caffeine and alcohol
The above two substances need no introduction. However, whilst we agree that dependency and overuse are best avoided, the full extent of their impact on sleep is often overlooked. Both substances impact a sleep-regulating hormone called adenosine, which builds up throughout the day. After around 16 hours, you should have enough adenosine to fall asleep soundly. A good quality 8-hour sleep is enough for the brain to remove the build-up of adenosine so that you wake up feeling refreshed and no longer sleepy. Caffeine inhibits adenosine, causing wakefulness; alcohol boosts it, causing sleepiness.
Caffeine hijacks your adenosine receptors and blocks them, which stops your brain from receiving the message that it is sleepy. In addition, caffeine has a half-life of around 6 hours and a quarter-life of around 12 hours. This means that a quarter of the caffeine from your midday coffee is still in your brain at midnight, tricking your brain into wakefulness. Whilst some claim to be able to sleep soundly after an evening espresso, studies have found that taking caffeine before bed causes a 20% reduction in deep sleep. This will reduce the amount of adenosine that is washed away overnight, resulting in morning grogginess. Morning coffees all round!
Meanwhile, alcohol does three things to your sleep. Firstly, it has a sedative effect. That nightcap isn’t making you fall asleep quicker, it’s making you lose consciousness quicker. Secondly, it fragments your sleep, meaning that you wake up more often during the night. Thirdly, it blocks your REM sleep, making you wake up unrefreshed and unrestored by your sleep. This can cause what is called “sleep inertia“, where you carry your sleepiness with you throughout the day.
What about THC and CBD?
According to Dr Walker, early research hints that CBD is promising, whilst THC may be detrimental to sleep. CBD is the non-psychoactive element of cannabis and THC is the psychoactive element. Acute use of THC can help you fall asleep faster, but coming off the substance can result in a rebound into insomnia as you can become dependent on its sleep onset benefits. Also, THC blocks your REM sleep just like alcohol does.
However, CBD offers the same sleep onset benefits without the dependency or rebound issues that come with THC. Moreover, early research indicates that CBD has no negative impact on your REM sleep either. It may also benefit sleep disorders including sleep apnoea. However, Dr Walker warns that too high a dose may encourage wakefulness and suggests that research should look for a sweet spot that offers optimal sleep benefits. CBD may also improve deep sleep, but the research is not yet conclusive.
CBD and anxiety
“We are constantly on reception. . . the only time that our brain goes from reception to reflection is when our head hits the pillow, and that’s the last time that you need to be ruminating and catastrophizing.” – Matthew Walker, PhD
CBD is known to be an efficient anti-anxiety substance. Dr Walker points to anxiety as one of the key causes of sleep problems worldwide. Hence, he believes that the non-psychoactive substance could improve sleep problems indirectly by reducing anxiety. It is almost impossible to sleep if your autonomic nervous system is pushed into a sympathetic dominance, your ‘fight or flight’ mode. Thus, CBD could help shift the autonomic nervous system into a more parasympathetic state.
Mental health: a two-way street
“Sleep is emotional first aid. Bottom line. Period.” – Matthew Walker, PhD
Sleep plays a crucial role in emotional regulation. Sleep deprivation and fragmentation are some of the strongest predictors of suicidality and suicide. REM sleep, in particular, provides essential overnight therapy as it resets the emotional networks in the brain. Without sufficient sleep, parts of our brains such as the prefrontal cortex and the amygdala miss out on essential emotional regulation, which can cause depression, mood swings, and reduced emotional control. Many parents will have experienced this first-hand. A lack of REM sleep can cause moody teenagers and disgruntled newborns, the latter of which spend 16 hours asleep each day and around half of this time in REM sleep.
Dr. Walker calls the relationship between anxiety and sleep deprivation a two-way street. Both amplify one another and can result in a destructive feedback loop. Dr. Walker noted that few mental health conditions present without some sleep issue and that sleep deprivation can result in symptoms associated with various mental health conditions. Thus, he suggests that sleep is perhaps an underlying cause of many mental health conditions, rather than a mere symptom or side effect.
How long can a human survive without sleep?
Most humans can only go without food for around 30-40 days, but the record length of time without food is 382 days. The longest period without sleep is 11 days. In other words, sleep deprivation is many times more fatal than food deprivation. In fact, sleep deprivation is so dangerous that Guinness World Records have actually banned attempts at the longest period of sleep deprivation. The approval of Felix Baumgartner’s record-breaking 39,000km skydive in which he broke the sound barrier as he plummeted to the earth at a staggering 1,357.64 km/h provides sufficiently shocking context to the dangers of sleep deprivation.
Sleep deprivation is rife in the medical profession
The medical profession’s relationship with sleep is laced with irony. Despite their awareness of the importance of sleep, many medical professionals are vastly underslept. Those who know doctors and nurses will undoubtedly have endless anecdotal evidence for this. Tales of 48-hour shifts, junior doctors working over 100 hours a week, surgeons sleeping in the hospital (if at all), and being on call 24/7. Dr Walker states that not only is this work ethic permitted, but it is actively encouraged and sometimes even expected.
Many, including Dr. Attia, believe this work ethic to be part of the very culture. He himself regularly volunteered to work demanding hours to impress his seniors and prove himself. He openly admits to having averaged around 28 hours of sleep a week as a resident and not a consistent 4 hours a night but 2 hours here, 6 hours there, half an hour there, and so on. This culture is toxic and unsustainable both for the professionals and their patients. Dr. Walker cites data that highlights a much higher chance of surgical and diagnostic errors with under 6 hours of sleep, never mind at the end of a 48-hour shift. He also cites that 1 in 5 medical residents will make a serious error during their residency due to insufficient sleep, whilst 1 in 20 will kill a patient because of insufficient sleep.
Road signs tell us the world over, and they are right. Motor vehicle accidents are the biggest accidental killer, thanks to recklessness, intoxication, mobile phones, and tiredness. When we are very tired, we experience microsleeps: fleeting, uncontrollable episodes of sleep which can last anywhere from a single fraction of a second up to 10 full seconds. Dr. Walker suggests that microsleeps are far more common than we might expect, and it’s much harder to regulate than drink-driving.
“Drunk reactions are slow. Microsleep reactions are non-existent.” – Matthew Walker, PhD
We live in a society in which sleep-deprived medical professionals finish a grueling shift, only to get into their car and drive home. Dr. Walker cites a quite unbelievable stat: after a 30+ hour shift, there is a 178% increase in the likelihood of a doctor crashing their car and ending up back in the same operating room but this time as a patient. Just let that sink in.
Put your knowledge into action
Now you know how sleep impacts diet and exercise, how caffeine and alcohol affect your sleep, and the relationship between sleep and mental health. You also have a wider appreciation for the impact of sleep in society. As you did in part one, pick one thing that you have learnt in this article and put it into practice. Perhaps you will maximize your sleep to maximize your gym gains or cease drinking coffee after midday to reduce that caffeine quarter-life?
Until next time.