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What Happens When We Don’t Sleep?

Have you ever felt the crippling effects of not sleeping enough? If you’ve ever pulled an all-nighter to study or worked a night shift, you know how quickly the effects of sleep deprivation can accumulate and make virtually every aspect of living more difficult the next day.

So then, what exactly happens when you don’t get enough sleep?

As you will see, not a single part of the human body is spared the damaging effects of sleep deprivation.

In this article, we will explore the effects of acute and chronic sleep deprivation on the brain and body. We’ll also see how long it takes to recover from not sleeping.

Sleep deprivation may be caused by something as simple as making more time for work and school activities or be the result of an undiagnosed medical problem. If you can’t get a good night’s sleep despite sufficient time and opportunity to do so, this may be due to an underlying sleep disorder causing insomnia

The effects of not enough sleep on the body

Acute and chronic sleep loss creates a whole host of negative physiological changes in our bodies. As we’ll see, a lot of the effects are cross-wired in your body. As sleep deprivation increases over time, there’s a compounding effect that takes place in the body.  

Cardiovascular effects of sleep deprivation

Sleep is a very rejuvenating time for the cardiovascular system. Our blood pressure and heart rate decrease significantly and our tissues regrow and repair.  Sleep deprivation increases the activity of the sympathetic nervous system, resulting in increased blood pressure, heart rate, and systemic inflammation. Systemic inflammation is increasingly being linked with the development of heart disease.

Chronic sleep deprivation is associated with an increased risk of cardiovascular disease, stroke, and coronary artery disease. Studies have shown that short sleep duration is correlated to a 48% increased risk of developing or dying from coronary heart disease and a 15% greater risk of stroke.[1] 

One study found that five or less hours of sleep per night is associated with a significantly increased risk of hypertension in middle-aged individuals.[2] These findings were supported in another study that showed that those who slept less than six hours per night were 66% more likely to suffer from hypertension than those who slept seven to eight hours per night.[3] Long-term hypertension is a major risk factor for stroke and heart disease.

Sleep deprivation weakens immunity

Sleep loss puts our body in a state similar to that found when we are under physical stress, and our immune system is no exception. Even just one night of four or five hours of sleep can impact our immune system considerably. 

In a study of 15 young men, 29 hours of extended wakefulness resulted in increased levels of a type of white blood cell called a granulocyte, directly mirroring the body’s stress response.[4] Granulocytes ingest and degrade foreign microorganisms and are important for mounting a response against flu, colds, and other invaders. 

However, a chronically increased amount of these white blood cells from sleep deprivation may play a role in the development of coronary artery disease through their secretion of substances that damage coronary arteries.[4]

In another study, one night of four or five hours of sleep also results in a 70% decrease in a type of immune cell called natural killer cells.[5] These immune cells are key players in preventing cancer by binding to cancerous cells and destroying them. 

This is one reason why sleep deprivation is associated with an increased risk of cancers, particularly cancers of the breast, prostate, and abdomen.[5] These natural killer cells returned to baseline levels after a few days of recovery sleep.

Our immune system is made up of a variety of immune cells that work in concert to fight off foreign invaders. One cell that has a broad influence on the immune response is the T-cell. This specific type of white blood cell plays an important regulatory role in immunity by helping mount an immune response through its action on other immune cells. 

Chronic sleep deprivation is associated with a suppressed immune response. Persistent lack of adequate sleep is associated with a lower T-cell count, and in turn, a reduced ability to fight off foreign pathogens. Additionally, the body responds to sleep loss by creating an inflammatory state, mediated by secreted proteins called pro-inflammatory cytokines.[6] 

The compounded result of increased inflammation plus reduced T-cell count due to chronic sleep deprivation makes our bodies more susceptible to bacterial and viral infections, even to such an extent that flu vaccines become less effective for individuals who are sleep deprived.[7]

Sleep loss leads to hormonal dysregulation

Hormones are important signaling molecules that play a regulatory role in our physiology and behavior. Sleep deprivation throws off the balance of several important hormones. Acute sleep deprivation increases the circulating levels of cortisol, epinephrine, and norepinephrine.[8] 

These hormones are implicated in our “fight or flight” response and raise our heart rate, blood pressure, and blood sugar levels. This may, in turn, increase our chances of cardiovascular disease and heart attacks.

Two other hormones affected are leptin and ghrelin. These hormones regulate satiety (feelings of fullness) and hunger, respectively. Short sleep duration is associated with decreased levels of leptin and increased levels of ghrelin.[9]

This results in an increased appetite and, ultimately, a higher body fat percentage. Indeed, chronically sleeping less than 5.5 hours a night is significantly linked to weight gain and obesity in both males and females.[10]

This is compounded by another hormone knocked off-kilter by lack of sleep, insulin. This hormone plays a role in regulating blood sugar by allowing our cells to metabolize carbohydrates such as glucose. 

Sleep deprivation causes increased levels of insulin, leading to increased fat storage and a higher chance of diabetes.[11]

Sleep deprivation and your skin

The common advice of “getting your beauty sleep” is actually very clinically supported. 

As we all know, even one night of not sleeping well can cause dark circles under the eyes and pale, dehydrated skin. However, more consistent sleep deprivation has a whole host of negative consequences on our skin. 

If we’re not consistently getting good sleep, our skin cells can’t repair optimally. In turn, our skin heals less quickly, our collagen production reduces, and our skin prematurely ages.[12] 

Making matters worse, the systemic inflammation caused by constant sleep deprivation can wreak havoc on our skin health, leading to conditions such as acne, psoriasis, eczema, and skin allergies. 

Sleep deprivation decreases libido

When we don’t get enough sleep, sex hormones like testosterone and estrogen reduce while stress hormones increase. This can lead to a decreased sex drive and even infertility.[13] 

Lack of sleep can age you more than a decade as far as libido and virility are concerned. In 10 young men who slept five hours for eight nights, testosterone levels reduced by 10% to 15%. To compare, normal aging reduces testosterone by about 1% to 2% per year.[14] 

For females, sleep deprivation can cause abnormal menstrual cycles and abnormal levels of reproductive hormones. An increase in total sleep time of one hour corresponded to a 14% increase in libido, according to one study published in The Journal of Sexual Medicine.[15] 

Sleep deprivation and the brain

Sleep deprivation results in sluggish information processing in the brain as a whole. It impacts a large range of cognitive functions, including memory, decision-making, concentration, and attention. 

Sleep loss also has a tremendous impact on our mood. It can cause temporary irritability and reactivity or, in the worst case, predisposes us to psychiatric disorders such as anxiety, depression, or even psychosis. 

We’ll also see how important sleep is to remove toxic metabolites that buildup during wakefulness.

Sleep deprivation prevents learning and memory formation

Sleep deprivation impairs the memory-forming apparatus in the brain called the hippocampus. When this region is disrupted from lack of sleep, we can’t commit new experiences to long-term memory. 

Unfortunately, no amount of catch up sleep will repay the sleep debt ensued on memory. In a study where individuals were deprived of sleep for thirty hours after training on a repeated visual task and then tested again after two full nights of recovery sleep, they showed no significant improvement despite being normally alert.[16]

As far as memory consolidation is concerned, sleep is an all-or-nothing event. We must sleep the night we learn, or we risk those memory traces degrading as quickly as they arrived.

Sleep loss impairs selective attention

In a recent study, researchers split participants into two groups, a control group who slept normally and a sleep-deprivation group who did not sleep for 24 hours. Both groups were instructed to listen to two different stories, one in each ear, at the same time. 

They were told to focus on just one of the stories. Those who slept normally performed significantly better at selectively attending to one story than the sleep-deprived individuals.  Studies suggest that one sleep period of eight hours can reverse the adverse effects of sleep deprivation on attention.[17]

Sleep loss leads to build-up of toxic proteins in the brain

As Matthew Walker says in his recent book Why We Sleep, wakefulness is akin to low-level brain damage that has to constantly be mitigated every night when we fall asleep. During wakefulness, toxic metabolites are produced that, in excess, clump up and kill nerve cells, a hallmark of dementia-related disorders like Alzheimer’s disease. 

During sleep, our brain is bathed in cerebrospinal fluid. This convective exchange with the fluid around brain cells washes away these neurotoxic proteins. Researchers have called this sewage system in the brain the glymphatic system.[18]

Just one night of sleep deprivation leads to an increase in a protein called beta-amyloid, the poisonous culprit behind Alzheimer’s disease.[19] Furthermore, this increase was found to occur in two regions of the brain that are impacted first in this disease, namely, the hippocampus and the thalamus. 

Neural damage caused by beta-amyloid can impair slow-wave sleep, which can result in more beta-amyloid accumulation which can further impair sleep in a vicious cycle. 

The sleep-deprived brain mimics an anxious brain

In a study from last year, researchers placed sleep-deprived subjects in a brain scanner and showed them distressing videos. In the individuals who did not sleep the previous night, the researchers observed heightened activity in the amygdala and dorsal anterior cingulate cortex, two regions of the brain involved in generating negative emotions like fear. This corresponded to a 30% increase in anxiety in these subjects.[20] 

Additionally, the researchers saw reduced activity in the medial prefrontal cortex in the sleep-deprived group. This region of the brain helps inhibit negative emotions. Without a well-functioning prefrontal cortex, we lack the ability to control negative emotions and may find ourselves irritable, reactive, impatient, and overall poorer communicators.

The anxiety in these individuals returned to baseline levels after a full night of sleep. However, if these brain regions are chronically hyperactivated (as in chronic sleep deprivation), the chance of developing an anxiety disorder is very high. 

On the other hand, chronic severe sleep deprivation, as is the case in total sleep loss, can bring on even more severe psychiatric symptoms such as hallucinations, visual distortions, depersonalization, and delusions.[21] This may also resolve after a few nights of recovery sleep.

Final thoughts

It’s clear that there are dire consequences to not sleeping, even for as little as one night. 

Sleep deprivation impairs many bodily processes, including our cardiovascular health, immunity, hormonal regulation, skin health, and libido. For our brain, being awake for longer than 16 hours starts to impair our cognition. 

Upwards of 19 hours awake and our mental capacity is similar to someone who is legally drunk. Microsleeps can occur during drowsy driving, where the driver experiences short bursts of sleep. This, combined with slower reaction times and deficits in attention, creates a much higher risk of car accidents. 

We also rely on sleep to clear out toxic metabolites and maintain the proper functioning of various brain regions. If we get less sleep than our body and mind require, we may be at risk of various psychiatric and neurological conditions in the long term.


Sympathetic nervous system: A part of the Autonomic Nervous System that activates our “fight-or-flight” response. 

T-cell: A type of white blood cell (lymphocyte) important for the immune response. They contain highly specific cell-surface antigen receptors. Subtypes include helper T cells, regulatory T cells, killer T cells

Pro-inflammatory Cytokine: A protein secreted by macrophages and helper T cells that promote inflammatory reactions in the body.
Memory Consolidation: Process by which a temporary, fragile memory is restructured and transferred into a stable, long-lasting memory.

Cerebrospinal Fluid: A protective fluid mostly made of water that flows in and around the hollow spaces of the spinal cord and brain.

Glymphatic System: A functional waste clearance system in the central nervous system of vertebrates. Word glymphatic comes a combination of the words glia and lymphatic. Glial cells are supportive cells found in between neurons that shrink when metabolic clearance occurs during sleep.



  1. Cappuccio FP,  Cooper D, D'Elia L,  Strazzullo P, Miller MA. (2011) Sleep duration predicts cardiovascular outcomes: a systematic review and meta-analysis of prospective studies, Eur Heart J , 
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  2. Walker, Matthew. Why We Sleep: The New Science of Sleep and Dreams.: Scriber, An Imprint of Simon & Schuster, Inc. New York, USA, 2017, 368 Pages.
  1. Asif, N., Iqbal, R., & Nazir, C. F. (2017). Human immune system during sleep. American journal of clinical and experimental immunology, 6(6), 92–96.
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  1. Taheri, S., Lin, L., Austin, D., Young, T., & Mignot, E. (2004). Short sleep duration is associated with reduced leptin, elevated ghrelin, and increased body mass index. PLoS medicine, 1(3), e62. 
  1. Kobayashi D, Takahashi O, Deshpande GA, Shimbo T, Fukui T. (2012). Association between weight gain, obesity, and sleep duration: a large-scale 3-year cohort study. Sleep Breath Schlaf Atm.;16(3):829–3
  1. Mesarwi, O., Polak, J., Jun, J., & Polotsky, V. Y. (2013). Sleep disorders and the development of insulin resistance and obesity. Endocrinology and metabolism clinics of North America, 42(3), 617–634. 
  1. Kahan V, Andersen ML, Tomimori J, Tufik S, authors. Can poor sleep affect skin integrity? Med Hypotheses. 2010;75:535–7. 
  1. Kloss, J. D., Perlis, M. L., Zamzow, J. A., Culnan, E. J., & Gracia, C. R. (2015). Sleep, sleep disturbance, and fertility in women. Sleep medicine reviews, 22, 78–87. doi:10.1016/j.smrv.2014.10.005
  1. Leproult, R., & Van Cauter, E. (2011). Effect of 1 week of sleep restriction on testosterone levels in young healthy men. JAMA, 305(21), 2173–2174.
  1. Kalmbach DA, Arnedt JT, Pillai V, Ciesla JA. The Impact of Sleep on Female Sexual Response and Behavior: A Pilot Study. J Sex Med. 2015;12:1221–1232
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