Why is sleep so important? — Transformative Insights

Humans sleep for about a third of their lives which means that anyone living to the current average age of 82 will have slept for a staggering 27 years. Whilst there is no absolute agreement yet on all aspects of sleep, research to date has firmly established that sleep is one of the key determinants of health, well-being, performance and the way we age.

Sleep is a core mechanism involved in the recovery and optimal functioning of our body as well as a complex process of "cleaning" up the brain (removing metabolic waste), processing the days events, laying down memories and learning. It is no surprise then that insufficient quantity or quality of sleep (over an extended period of time) is correlated with many illnesses, faster aging, cognitive impairments and decline as well as a shorter lifespan.

Research indicates that when we don't have good sleep and have variability in when we sleep or mis-timed circadian rhythms there is a four-fold increase in cancer risk and a multi-fold increase in the risk of developing diabetes, metabolic syndrome and cardiovascular disease. Other research revealed there is a 56% increase in the risk of obesity when we get less than 6 hours of sleep and yet another study showed that after one night of sleep loss healthy young adults became (temporarily) pre-diabetic.

The complex process of "cleaning up the brain" is particularly interesting and recent research has indicated that sleep plays a vital role in waste removal from the brain, with this waste removal being twice as fast during sleep as during our awake hours. During sleep our brain cells shrink by about 60%, creating more space and make it easier for cerebrospinal fluid to flow past our brain cells, taking (more) waste with it.

The result is that our brain gets restored and we wake up feeling refreshed and with a clear mind and we may be preventing the (early) onset of various neurological disorders. For example, the brain’s metabolic waste includes proteins (amyloid-beta proteins) that have been implicated in the development of Alzheimer's disease - a finding that provides further insight into how sleep influences how we age.

Sleep and memories is also an interesting domain and sleep expert Matthew Walker says "We sleep to remember, and we sleep to forget". When you sleep well you focus, learn and retain information better. And during specific stages of sleep new connections are made in the brain which help consolidate memories. Surprisingly though Matthew's research indicates that sleep also does something powerful with painful memories. Turns out that during REM sleep the emotional charge related to painful memories is reduced.

A study, dubbed the "World's Largest Sleep study" (over 10,000 participants)
demonstrated there is a U-shaped relationship between sleep and cognitive ability, such that shorter and longer habitual sleep were linked with poorer cognition. Sleeping 1 hour more than usual during the night before cognitive testing was associated with optimal cognitive performance, but sleeping both less than usual or 2.5 hours more than usual were associated with poorer cognitive performance. It seems there is a “Goldilocks” amount of sleep—not too little, not too much—that best supports complex cognition.

Sleep is also vital element of our recovery. Failing to get the right quality and / or quantity can have a knock-on effect on virtually every aspect of our lives. From our executive functioning (learning, memory, decision-making, attention, problem solving), cognitive processing / reaction times, mood, emotional self-regulation, energy levels, health and longevity through to our productivity at work and our ability to cope under pressure.

Sleep interestingly enough is also key to our weight management - sleep ensures our hormones involved in energy regulation remain balanced. Insufficient sleep reduces leptin which is a hormone that helps to regulate energy balance by inhibiting hunger.

Recent research has also shown an important connection between sleep and our immune system. For example one study found that those with less than seven hours of sleep per night were nearly three times as likely to develop a cold, compared to those who got at least eight hours of sleep.

And compounding all of these impacts is that studies show that, when we are in a sleep deprived state, we grossly underestimate these impacts and believe we are much less affected than what test results demonstrate. In a sleep deprived state we also experience heightened emotional reactivity (our limbic, more primal, part of the brain is more active) combined with suppressed cognitive control (our prefrontal cortex is less active) and as such we make poor decisions and take more risks. This of course includes decisions about healthy behaviours (including a decision for example whether or not to get more sleep) and so we fall into a vicious circle that erodes our health.

Even a loss of sleep as little as one to two hours during one night leads to what we call "effort discounting". This means we are less likely to make an effort towards something we (normally) value, for example getting to bed earlier to have sufficient sleep.

In summary then, and just to emphasize the importance again, sleep is the cornerstone of our overall well-being, health and functioning as well as an important contributor to our life and health-span (the amount of years during which we experience good health).

Despite the important functions sleep it fulfills, we have come to regard sleep as a barrier to getting things done in our modern "always-on" and results driven society. We have downgraded its importance and often feel we can sleep and catch up on it as some point in the future. In reality sleep is a fundamental daily activity that benefits from being ranked at the same (or ideally higher) level of importance as our other daily activities.

When we value sleep appropriately, allow the natural sleep processes (see the Natural Processes blog) to do their job and experience good sleep, we actually set ourselves up to perform better for longer in our “alway-on” society, while also looking after our physical health and mental well-being.