Useful Sleep Facts: Here’s All You Need To Know

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Sleep is so crucial to our overall wellbeing, yet most of us don’t get enough of it. When balancing exam preparation with a full-time job, it’s tempting to cut on sleep hours in a bid to “do more”. But this is counterproductive in the long term.

With so much conflicting information out there on sleep, here’s a no-nonsense, researched-backed summary of sleep facts you need to know to invest in your wellbeing.

Let’s find out!


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How sleep works

It’s worth spending some time understanding sleep, since we spend (hopefully) around 1/3 of our lives doing it!

There are basically 2 main factors that regulate sleep naturally:

  • Circadian rhythms, which is our internal “body clock” that manages when we are awake and when we are ready to sleep. It responds to light exposure and controls the production of the melatonin and cortisol hormones. When it is dark, production of melatonin hormones are increased which helps us feel sleepy. When it is bright, cortisol hormones are produced to help the body wake up.
  • Our “sleep drive“, which is like a gauge that builds up our craving for sleep throughout the day. The longer we go without sleep, the faster we reach a certain point where we need to sleep.

However, there are so many external factors that can disrupt the natural circadian rhythm and sleep drive. Here are some examples:

  • Electronic devices’ lights reduces melatonin production and makes us less sleepy (than we should).
  • Drinking caffeinated drinks drives up cortisol levels which makes us more alert.
  • Working night shifts or having jet lags messes up our internal body clock due to irregular light exposure.
  • Having a nap late afternoon replenishes the sleep drive and we are less sleepy at our usual time because of that.

[There are 2 types of sleep: REM (rapid eye movement) sleep and non-REM sleep.

When we fall asleep, our body temperature drops, brain activity, heart rate and breathing slows down too. We then go through various sleep stages of varying lengths.]

[POINT OF REM VS NON REM SLEEP? RESEARCH INFO]


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Why is sleep important?

Sleep is crucial for our overall wellbeing.

It ensures the proper functioning of nearly all the systems in the human body, ranging from physical and mental development, immune system, metabolism, cardiovascular health, brain functions, general mood and more.

To put it simply, investing your time in getting sufficient, good quality sleep is the best long term investment in your overall health.

Looking at this on the flip side, the importance of sleep can be seen when we examine the symptoms and effects of sleep deprivation in the following sections.

[In humans, sleep appears to be critical to both physical and mental development10 in babies, children, and young adults. In adults, a lack of sleep has been associated with a wide range of negative health consequences including cardiovascular problems11, a weakened immune system12higher risk of obesity and type II diabetes13, impaired thinking and memory, and mental health problems like depression and anxiety.

Not getting enough sleep or enough quality sleep raises your risk for heart and respiratory problems and affects your metabolism and ability to think clearly and focus on tasks.

Getting inadequate sleep over time can raise your risk for chronic (long-term) health problems. It can also affect how well you think, react, work, learn, and get along with others.]


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Lack of sleep symptoms

Here are the typical signs of sleep deprivation to look out for:

  • The tendency to doze off when sitting, whether it’s reading, watching TV, during a car ride, meeting or even talking to someone!
  • Feeling groggy when waking up in the morning
  • Easily irritable, tired, and constantly yawning
  • Lack of energy and ability to focus
  • Poor memory
  • Weaker immune system

sleep deprivation

Effects of sleep deprivation

The effects of sleep deprivation are well researched and documented, for example:

  • Attention lapses and cognitive declines, e.g. reduced productivity and terrible decision making.
  • Prone to accidents, especially when driving.
  • Increased health risks: diabetes, high blood pressure, stress, mental illnesses, depression.
  • Blackouts or micro-sleeps, where one unconsciously falls asleep for 1-30 seconds no matter what he/she is doing at that time.
  • More likely to behave unethically at work.
  • Weight gain, obesity.
  • Perceived as less attractive (there is such a thing as beauty sleep!)  

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How much sleep do adults need?

OK, so to avoid sleep deprivation, how many hours of sleep should we aim for?

The general consensus here is that adults on average need 7-9 hours of sleep, depending on your age.

For those 38 years and older, research has shown that 7 hours of sleep consistently is ideal, no more, no less.

For the rest, 8 hours of sleep is ideal as there isn’t any significant benefit of increasing sleep to 9 hours.

To support the statements above, let’s take a deep dive into a few interesting deprivation studies.

In their study that took place over 1998-2002, David Dinges and Hans Van Dongen assigned their 48 subjects aged 21-38 into 3 different groups that had 4, 6 and 8 hours (control group) of daily sleep respectively for 2 weeks.

Every 2 hours during the day, the researchers tested the subjects’ ability to sustain attention with what’s known as the psychomotor vigilance task (PVT), considered a gold standard of sleepiness measures. It’s a simple test that measures the subject’s level of sustained attention through the amount of response delay.

Here’s what they found:

  • 6 hours and below isn’t enough. Not surprisingly, those that had 8 hours sleep throughout the 14 day study hardly had any attention lapses or cognitive decline. Those on 4 and 6 hours of daily sleep had PVT results that decline steadily each day, with 4-hour-sleepers performing worse (as expected). 
  • It takes time for effects to emerge. By the 6th day, 25% of the 6-hour-sleepers were falling asleep at the computer. By the end of two weeks, the 6-hour sleepers were as impaired as those who, in another Dinges study, had been sleep-deprived for 24 hours straight — the cognitive equivalent of being legally drunk.

Conclusion: Become sleep deprived enough, and it’s the same as being drunk at work. Minus the fun part of, you know, being drunk.

OK, what we have learned so far is that 8 hours of quality sleep is good, but 6 hours or less is insufficient for proper functioning.

So, is there an optimal level of sleep?

Luckily for us, Dinges’ study was supplemented by his colleague Gregory Belenky, who ran a similar study with 66 subjects aged 24-62 sleeping 3, 5, 7 and 9 hours daily. 

Belenky’s study found that the 9-hour-sleepers performed similarly to the 8 hour ones, yet the 7-hour-sleepers showed continuous decline in PVT performance for 3 days, before stabilising at lower levels than when they started. 

With most of us sleeping an average of 7 hours, it seems that we are not as sharp as we could.​

However, the 2 studies above have a relatively small sample size with a broad range of age group, which may not have fully considered the impact of sleep needs as we age.

In one of the largest sleep study done by University of Cambridge and Fudan University which examined nearly 500,000 adults aged 38-73 years old, researchers found that 7 hours of sleep consistently is ideal for ‘middle and old age’, i.e. 38 years and above. Any more or less sleep than that is associated with poorer mental health and cognitive performance.


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Can we learn to sleep less?

Apparently not, according to Dinges’ study – it’s genetics

In Dinges’ and Van Dongen’s study: after just a few days, the 4 and 6 hour sleepers reported that they were slightly sleepy, but were adamant they had adjusted to their new state. 

Even 14 days into the study, they said sleepiness was not affecting them, when in fact, their PVT performance had tanked.

This leads us to conclude that the sleep-deprived among us are lousy judges of our own sleep needs.

So what about Einstein or Edison, I hear you ask?

Albert Einstein acknowledged his need of 10 hour sleep for optimum performance whilst Thomas Edison believed that it was a waste of time, survived mostly on frequent naps.

According to the studies, these examples seem to be the extremes. Less than 5% people can maintain performance on 5 hours or less of sleep genetically, whilst another 5% or less require 9 or 10 hours.


how to focus when studying even when you are tired

Can you catch up on sleep debt?

Sleeping less will accumulate on you, eventually.

There are 2 types of sleep debt: acute (short term) and chronic (long term). Acute sleep debt is calculated as the sleep deficit accumulated over the last 2 weeks, whereas chronic sleep debt is sleep deficits that have been accumulated over years.

“You don’t see it [being sleep deprived] the first day. But you do in 5-7 days. Unless you’re doing work that doesn’t require much thought, you are trading time awake at the expense of performance.”

George Belenky’s 2002 sleep deprivation study

Given the negative effects of sleep deprivation, it makes sense to take action now to catch up on sleep debt.

The good news is that you can catch up with sleep, if it is acute sleep debt, just by catching up on the extra sleep you missed. Even so, reversing acute sleep debt doesn’t happen overnight as it can take over a week to fully recover from it. We will look on how to catch on sleep properly in the next section for a better rate of recovery.

However, it doesn’t mean that those with chronic sleep debts are doomed, as we simply don’t know the possibility of this yet, current research on this is inconclusive. Most chronic sleep debts sufferers have acute sleep debt anyway, so increasing the sleep amount consistently to meet your sleep needs would still help those with chronic sleep debt as a first step.


how to manage study with full time job

How to cure sleep deprivation

If you’re still experiencing daytime sleepiness or difficulty sleeping, first port of call is to speak to your doctor to see if there are any other underlying conditions contributing to this.

Otherwise, if there are no underlying medical condition, check out our comprehensive guide on how to sleep better to establish a better sleep hygiene and bedtime routine.

It’s important to be patient and give it time for your new routine to show results, since it takes more than 1 week to reverse the effects of a 1 hour acute sleep debt anyway.

While napping helps in the short term, it doesn’t provide the long term restorative benefits of nighttime sleep, so it is just a temporary measure that pushes the problem further down the road.

As mentioned earlier, those who are sleep deprived do adjust to their state chronic sleep restriction, without realising that their cognitive, physical and mental health performance have declined.

Some may think sleeping excessively on a weekend may help, but only a consistent daily bedtime routine would help in the long term as it doesn’t upset your body’s circadian rhythm.

If you can, it’s best to avoid the problem of sleep deprivation to begin with, and prioritize your health and wellbeing by prioritizing sleep. The actual payback period to reverse its negative impacts (if it is possible at all) takes significant longer than one expects.


Sleep facts: Key takeaways for your exam preparation

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  • You can’t cheat on sleep in the long runPlan a sustainable study routine and a healthy sleep habits.
  • Don’t try to cram the night or week before your exams without much sleep. It actually decreases your chance of passing, and you don’t want that do you? (But if you are forced to cram, here are some tips.)
  • Unless you’re one of the rare few that requires less (say 5 hours) or more (9-10 hours) since young, here are the optimal sleep hours for most adults:
    • If you are 21-37 years old, 8 hours of daily sleep is optimal
    • If you’re 38 years old and above, 7 hours of daily sleep is optimal.
  • You can’t train yourself to need less or more sleep, unfortunately.

Hope you found the research-backed sleep facts above useful! This is one of a two-part series on sleep. The other part details how to improve your current sleep patterns for better quality sleep that you need. Let us know what you think in the comments below!

Meanwhile, you may find these related articles of interest:

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2 thoughts on “Useful Sleep Facts: Here’s All You Need To Know”

  1. “Wow, I feel really tired today…I wonder if my study schedule is a little too intense…let me check 300 hours…wow, look at that, an article on sleep deprivation.” That’s pretty much how my morning went. Haha what good timing. Another great, and almost prescient, article!

    Reply

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