When was the last time you remember waking up for work without an alarm, feeling refreshed and ready to go? If you can’t think of the last time you did, then you’re not alone. Two thirds of adults in developed nations reportedly don’t get the recommended 8 hours of sleep a night.

 Chronic sleep deprivation is defined as getting less than 7 hours of sleep a night on a routine basis. In part 1 of this series, we talked about what happens during the different stages of sleep and how much humans really need. Today, we will go through seven short-term consequences to human health and function as a result of chronic sleep deprivation. Long-term consequences such as the development of early onset Alzheimer’s, type II diabetes, cardiovascular disease, stroke, and even cancer have been causally linked, but will be discussed another time.


  1. Physical performance
    Have you ever had a poor night’s sleep, and been completely frustrated to find that your warm-up weight feels terribly heavy and slow, or that you just can barely breathe during your run?Research shows that on six hours sleep compared to eight, the time to physical exhaustion drops by 10-30%, blood oxygen saturation and aerobic output is significantly reduced and the body’s ability to cool down through sweat is impaired, which reduces aerobic endurance and makes it harder to catch your breath.On the other hand, limb extension force and vertical jump height is impaired, peak sustained muscle strength is decreased and lactic acid builds up faster, which decreases absolute strength, power and speed in the gym and out on the field.
  2. Injury prevention
    As well as a reduction in physical performance, injury risk rises significantly as a result of lack of sleep. A study by Milewski et al (2014) has showed that reducing sleep from 8 hours to 6 hours increases risk of injury from anywhere between 35% to 73%.
  3. Skill memory
    There’s a story of a pianist who was learning a new musical piece one morning, and kept practising throughout the day without having much success with playing the music well. After giving up for the night and heading to bed, he woke up the next morning to resume from where he left off yesterday, and surprised himself by playing the piece perfectly. This is one instance, where sleep has shown to help with skill learning and consolidation, where the brain can improve skill memory in the absence of any further physical practice.Think about the same improvements when practicing your max deadlift or squat, or even with running training!
  4. Body composition
    Have you noticed that on the days where you have had inadequate sleep, you’ve experienced strong cravings for sugary, salty and carbobydrate-rich foods? You’re not alone.Dr Eve Van Cauter from the University of Chicago has been studying the link between sleep and appetite over the last three decades. Her findings have confirmed that under sleep deprived conditions where participants only had 4.5 hours in bed versus 8, cravings for salty and carb-loaded foods surged by 30-40% and food intake increased by 300 calories on average per day. The reason for this correlation is due to an imbalance in two hormones related to appetite: Ghrelin, which is responsible for appetite and huger and Leptin, which signals satiety. When sleeping less than 6 hours compared to 8, circulating levels of Ghrelin is increased, while Leptin is supressed. As a result, sleep deprivation has been highly associated with accelerating weight gain, obesity and type II diabetes.
  5. Concentration
    A brain function that is affected with the slightest level of sleep deprivation is concentration. Lapses of concentration can present as a general ‘foggy brain’, but also through micro-sleeps, where the brain stops responding to external cues for up to a few seconds. This is most damaging within society in the form of fatal car accidents. After being awake for 19 hours, concentration is as bad as being legally drunk. On only 5 hours sleep, the risk of a car crash rises to three times as likely. On less than 4 hours, the risk increases to a whopping 11.5x.
  6. Memory learning and consolidation
    It’s incredible how there is a culture of ‘pulling all nighters’ in uni students to study for exams. If only they knew about the effects of sleep deprivation on memory, maybe it’s not worth sacrificing sleep only to retain very little information.During sleep, proteins are produced to form synapses between neurons in the brain for memory learning and consolidation. Without sleep, memories evaporate quicker as they cannot be transferred from short-term storage to long-term memory. This has been shown through research of participants who learn a sequence of characters, and are asked to reproduce the sequence a few hours later, after some had been allowed a nap and others without. Those who napped performed consistently much better than those who stayed awake.
  1. Emotions
    Maybe you have noticed that at night, you and your partner often get into aggressive arguments, yet once you ‘sleep on it’, the intense emotions completely disappear the next morning?Sleep accentuates activity in the prefrontal cortex of the brain, which involves logical thinking and problem solving. However, under sleep deprivation or past the 16 hour recycle rate of human beings, activity of prefrontal cortex is inhibited. Instead, activity within the emotional centres of the brain (Amygdala and Striatus) are emphasized, causing transversing between these two centres within a short amount of time, creating extreme mood swings and exaggerated emotions, seen in bipolarism.

So what now?
By now, most of you are aware that even one night of poor sleep can have profound effects on the mind and body. Combining this with the inability to fully-catch up on lost sleep, it’s imperative that humans make a conscious effort to spend at least 8.5 hours in bed each night, to allow for the time spent falling asleep and nocturnal awakenings. Every adult is ‘busy’ in one way or another, but never busy enough to trade-in one’s own health for a reduced quality of life and even life expectancy.