Sleep duration

Understanding sleep duration

To sleep restoratively, we must sleep sufficiently. Without spending enough hours in bed and time asleep, our bodies and minds lack the opportunity to restore, replenish, and repair. While the old adage advises eight hours of sleep, the CDC prescribes between seven and nine.

Sleep duration - or Total Sleep Time (TST) - is simply the total number of hours, minutes, and seconds you spend asleep each night.

Willingly or otherwise, we consistently fall short of getting enough sleep. Late nights in the office push our bedtimes back. Early-rising children haul us from our beds at the crack of dawn. Social norms have persuaded us that sleeping is akin to laziness - a myth that deprives us of what we so dearly need.

We have stigmatized sleep with the label of laziness. We want to seem busy, and one way we express that is by proclaiming how little sleep we’re getting. It’s a badge of honor. Humans are the only species that deliberately deprive themselves of sleep for no apparent reason.

Matt Walker,
The Guardian

dr. matthew walker

Why sleep duration matters

Getting fewer hours of sleep means you also have less opportunity for healthy sleep.

It limits the opportunity for light sleep, the generalist sleep stage behind a gamut of functions, including memory, body repair, and hormone regulation. It reduces our deep sleep, hindering our bodies’ ability to replenish energy, repair muscle, and reinforce our immune systems. It cuts away our REM sleep, destabilizing our emotional counterbalance.

Without sufficient hours in bed and sleep, we lose the superpower of sleep.

What if we don’t get enough?

We cannot stay awake forever. There comes a point in time when our bodies and minds begin to deteriorate, after which we need sleep to recover.

The recycle rate of a human being is around sixteen hours. After sixteen hours of being awake, the brain begins to fail. Humans need more than seven hours of sleep each night to maintain cognitive performance.

Matt Walker,
Why We Sleep

dr. matthew walker

Depriving our minds and bodies of sleep means we never return to our optimal condition. Sleep deprivation need not be extreme, either. Just 10 days of six hours of sleep will impair cognitive performance as much as going without sleep for 24 hours.

The detrimental effects of sleep deprivation are not rendered equally. Sleep is not uniform. It has a natural cadence and flow, cycling through five discrete sleep stages. The composition of each cycle changes through the night, with REM sleep more prevalent in the final hours before waking. Sleeping too little costs us a disproportionate amount of these latter stages.

The message is clear: to improve sleep quality, we must sleep long enough.

How can I improve sleep duration?

In an ideal world, we would carve out a consistent seven to nine hours for sleep - but life so often renders this impractical or impossible.

When we have precious few hours available for sleep, we must prioritize the habits and behaviours we can control. By building routines and environments that nurture sleep, we can enjoy the most benefits from each hour we spend in bed.

First, we must get to sleep.

Create a calming sleeping environment: add blackout curtains or blinds; remove excess light sources; nix disruptions like phones. Build a sleeping routine, one that brings you down gently.

Falling asleep is like landing a plane. It takes time. You've got to sort of gradually descend. I think one of the problems with insufficient sleep is people are not very good at predicting how poorly they are doing when they are under-slept.

Matt Walker,

dr. matthew walker

Then, we must stay asleep.

Avoid substances known to disrupt sleep—caffeine and sugary foods are two common culprits. Be mindful, too, of those like alcohol and sleeping pills, substances that induce non-natural and non-restorative sleep. Learn more about maximizing your sleep efficiency.

Finally, we must embrace our biology.

Two processes dictate our tiredness: sleep drive (process S) and circadian rhythms (process C).

The former is heavily reliant on our behavior the previous day. The longer we are awake, the more tired we feel. That feeling dissipates rapidly during sleep. We also see influence of chemicals like adenosine, melatonin, cortisol, thyroid, sex hormone, and others.

Circadian rhythm - the 24-hour body clock regulating internal processes and alertness - is independent of such factors. However, it is influenced by meals, alcohol, exercise, stress, naps, temperature, and medications.

Everyone has a unique circadian rhythm, although most fall into either morning or evening chronotypes. Morning larks wake early in the morning and retire early at night. On the other hand, night owls rise late and stay awake into the small hours.

Misaligning our sleeping habits and natural chronotypes is like fighting biology - and there will only ever be one winner.