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What Happens In Your Body When You Don’t Get Enough Sleep

Most people believe that sleeping is a passive act. However, when you are asleep, your body is very active as it repairs injuries, balances hormones, and regulates the immune system.

Reviewed by Dr. Jose Angel Barrientos, ND

Also, your brain actively reviews what happened in your day and decides which memories to keep and which ones to forget (synaptic pruning). 

Sleep is so important for your body that going just one night without enough sleep can leave you feeling irritable and unable to focus. You may also look sadder, tired, and even older than you actually are. 

First, let’s look at what happens in your body and brain during sleep.

How Your Body And Brain Works During Sleep

1. Cleans Up Your Brain

During sleep, your glymphatic system (your brain’s housekeeper) keeps neurons in your brain healthy. This system removes waste products from the brain and spinal cord. It also delivers glucose, lipids, amino acids, and neurotransmitters. 

When you are awake, the glymphatic system is suppressed. When you are asleep, your glymphatic system becomes more active as the flow of cerebrospinal fluid (CSF) rises. CSF is a special fluid that bathes the brain and spinal cord and provides nutrients and protection. 

The increase in CSF flow can help remove accumulations of unhealthy proteins from the brain and may be protective against neurodegenerative conditions. 

2. Damage Reparation And Restoration Of Hormones And The Immune System

During sleep, your body releases hormones that instruct cells to repair sore muscles and wounds. Sleep also allows your body to balance hormones that may have been increased during a hard day at work, such as the stress hormone cortisol. 

The immune system, especially the adaptive immune system, is also busy during sleep. This system is responsible for:

  • Making antibodies
  • Forming long-lasting memories against specific bacteria and viruses
  • And launching quick, targeted attacks on pathogens

What Happens When You Don’t Get Enough Sleep

1. Thrown Off Circadian Rhythm

Sleep deprivation interferes with your circadian rhythm and very important body clock processes that happen during sleep. The circadian rhythm is the 24-hour internal clock in your brain that makes sure your cells do the right things at the right times of day. A disruption of the circadian rhythm can affect every system in your body.

To sync your body clock with the 24 hour clock of the earth rotating on its axis, your brain uses environmental inputs. These include light exposure, sleep/wake times, temperature, and mealtimes. When you expose your eyes to morning sunlight, you are essentially updating your circadian rhythm and telling your body that this is the start of your day. 

For blind people, their amazing brain relies on changes in temperature, such as the increase in temperature when the sun rises or the drop in temperature after it sets, to update its circadian rhythm. Conversely, a thrown off rhythm can make it hard to fall asleep or get good quality sleep.

2. Increased Inflammation And Weakened Immune Response

Poor sleep can disrupt immune functions and increase inflammation. Also, elevated cortisol from sleep deprivation can be stressful for the body, increasing cortisol. These changes can weaken the immune system and slow down wound healing. It’s no surprise that being sleep deprived could mean you get sick easier and heal slower.

3. Increased Stress Response And Sympathetic Nervous System Activation

The sympathetic nervous system increases heart rate and breathing, and decides if you should fight or flight in a stressful situation. Sleep deprivation can make you more fight-or-flight than rest-and-digest overall. This can lead to an increase in heart rate and blood pressure. Overall, it reduces your stress resilience and reserve.

4. Poor Blood Sugar Control And Insulin Resistance

Sleep heavily influences your insulin response, insulin levels, and even affects the cells in the pancreas that make insulin. In healthy adults that were sleep deprived for just one day, their labs showed signs that their bodies were not using blood sugar properly and became more insulin resistant. 

5. Undesirable Hormonal Changes

Growth hormone can help neurons, muscles, and bones grow. It also supports wound healing and tissue repair. At night, growth hormone is normally released in a pulse-like pattern (growth hormone surge). Sleep deprivation suppresses growth hormone. In some cases, its surge completely disappears the night of sleep restriction.

In a study of 160 healthy and normally cycling women, aged 19 to 44 years, follicle-stimulating hormone (FSH) levels were 20% higher in long-time sleepers than in short-time sleepers. FSH helps control the menstrual cycle and stimulates the growth of eggs in the ovaries.

Normal aging is associated with a decrease of testosterone levels by 1% to 2% per year. In a small study of 10 healthy men, sleep deprivation dropped their daytime testosterone by as much as 15%.

6. Unhealthy Gene Readouts

In a study of 26 healthy men and women, insufficient sleep affected a total of 71 genes by activating and deactivating. These genes were associated with:

  • Metabolism
  • Oxidative stress
  • Responses to stress
  • Immune function
  • And even the structure and organization of DNA (chromatin remodeling).

7. Less Healthy Gut Flora

In animal studies, sleep deprivation could cause an imbalance in the bacteria that lived within their gut (dysbiosis). Their intestines also showed more leaky gut. Scientists believe that this may be caused by a dysfunction in circadian genes from poor sleep. 

The sleep restricted animals also experienced more anxiety, possibly, due to the imbalanced gut bacteria releasing chemicals that worsened brain inflammation.

8. Increased Risk Of Weight-Gain

People who habitually sleep less than 7 hours are more likely to get fat than those with normal sleep habits (generally 7–8 hours of sleep a night). There are many things that may explain this finding, some of which include:

  • Poor sleep affecting hormones that control appetite, such as leptin and ghrelin [R10]. Leptin decreases hunger, whereas ghrelin increases hunger. Inadequate sleep lowers the levels of appetite-suppressing leptin and increases the levels hunger-driving ghrelin.
  • Sleep loss increases levels of circulating endocannabinoids (chemicals produced by the body that are very similar to those in cannabis). These endocannabinoids, like in people that use marijuana, stimulate appetite and increase the desire to eat snacks, aka “the munchies”.
  • You become less motivated to exercise due to the tiredness. After a long day at work and a short night of quality sleep, you’re less likely to hit the gym.
  • Your prefrontal cortex, the part of our brain that is involved in thoughtful judgments and controlled decisions, becomes less active. High-calorie foods become significantly more desirable in healthy and fit participants who were sleep deprived. 

This happened even when they were allowed to eat by themselves (to avoid any judgements from other people), and after being offered foods ranging from vegetables, fruits, and meat, to potatoes, bread, and ice cream.

  • Sleep deprived people eat about 300 more calories each day than when they were resting adequately. This may not sound like a lot, but what if we were to do the math for a person that is sleep deprived 5 days out of the week due to work. At the end of a year, that person would have consumed an extra 70,000 calories (or gained about 10 to 15 lb of weight that year).

Walker, M.P. (2018) “Cancer, Heart Attacks, and a Shorter Life, Sleep Deprivation and the Body” in Why we sleep: The new science of sleep and dreams. London, UK: Penguin Books. 

9. Elevated Risk For Serious Outcomes

Many studies show that sleeping less than 6 hours is associated with an increased risk of an early death due to accidents (e.g. people falling asleep while driving). There is also an increased risk of developing metabolic and cardiovascular diseases, such as:

  • Type 2 diabetes
  • Stroke
  • Hypertension


We hope we’ve shared enough science behind the importance of sleep. The consequences of sleep deprivation may not be worth it if you want to feel and be healthy. Sleep deprivation reduces your brain’s ability to self-cleanup, throws off hormones and immune systems, and impairs healing. 

It also:

  • Throws our circadian rhythms and blood sugar levels out of sync
  • Increases inflammation and stress
  • Changes the expression of our genes and microbiome
  • And can increase our risk for serious accidents or disease

You cannot mitigate these negative health effects of sleep deprivation with coffee or any supplements.

Life is full of surprises, from studying for an exam or having to work overtime. And occasionally we will have to deprive ourselves of quality sleep. If you’d like to know about how you can better recover after a night of sleep restriction, then be sure to check out our next article How to Recover from Sleep Deprivation.

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