What one night of sleep deprivation does to us?
Discover how even one night without sleep affects your brain, genes, and health. Learn the signs of sleep deprivation and how to combat it.
Many people believe they can function normally on just 6 hours of sleep per night. A 2003 study by Hans Van Dongen showed that healthy participants who slept for 6 hours for two weeks performed at the level of people who had been awake for two consecutive days on attention and reaction tests. At the same time, the participants themselves reported feeling fine, and their subjective sense of fatigue did not increase. This indicates the brain's inability to adequately assess the extent of its own sleep deprivation.
Definition of Sleep Deprivation and Its Prevalence
The American Academy of Sleep Medicine and most national guidelines define normal sleep for adults as 7-9 hours each night. Less than 7 hours is considered short sleep, and less than 6 hours is considered chronic sleep deprivation. For teenagers, the norm is 8-10 hours, and for children, it is even more.
There are so-called "short sleepers" who only need 3-4 hours of sleep. However, as a rule, these are people with genetic polymorphisms, making up an extremely small fraction of the population (less than 0.1%). Most of those who consider themselves "short sleepers" have actually just adapted to such a regimen.
Signs of Possible Sleep Deprivation
While there is no 100% accurate test for sleep deprivation, several markers can be identified:
- Need for an Alarm Clock: If the body receives enough rest, it is capable of waking up on its own before or at the same time as an alarm clock. A constant need for an alarm clock and the ability to sleep longer without one indicate a lack of sleep.
- Increased Sleep Duration on Weekends: Sleeping 1.5-2 hours longer on weekends can be indicative of sleep deprivation during weekdays.
- Instantaneous Falling Asleep: Falling asleep within 1-3 minutes of lying down in bed, as opposed to the normal 10-20 minutes, indicates excessive accumulation of "sleep pressure."
- Drowsiness in Quiet Environments: Feeling drowsy during meetings, on public transport, while reading, or in other quiet situations.
- Caffeine Dependence: The need to consume coffee to wake up and function normally.
These signs may be minor individually or occur periodically. However, their combination and prolonged presence are cause for concern. It is also important to consider not only the number of hours spent in bed but also the quality of sleep.
Mechanisms of Sleep Deprivation's Impact on the Body
Sleep deprivation disrupts the body's functions at various levels, from cellular to genetic.
Brain Tissue and the Glymphatic System
The brain lacks a developed lymphatic system, and the clearance of cellular waste products occurs through the glymphatic system. During sleep, the interstitial space in the brain expands by approximately 60%, which intensifies the outflow of waste, including beta-amyloid, linked to the development of Alzheimer's disease. This process is most active during deep, slow-wave sleep. Studies from 2018 showed that after one sleepless night, amyloid levels in the hippocampus and thalamus increase by about 5%. Similar changes are observed for tau protein, also associated with neurodegenerative processes. Thus, sleep deprivation leads to a "clogged brain."
Cellular Level and Adenosine
Every cell uses ATP as an energy source. In the process of cellular work, adenosine remains, which accumulates in the brain throughout the day. Adenosine binds to A1 receptors on neurons, signaling the need for rest. This accumulation of adenosine is one of the reasons for the sensation of "sleep pressure." During normal sleep, adenosine is washed out of the brain, and ATP stores are replenished. Caffeine blocks adenosine receptors but does not eliminate adenosine itself, which only temporarily masks fatigue.
Synapses and Synaptic Homeostasis
The theory of synaptic homeostasis suggests that synapses (connections between neurons) strengthen throughout the day. During sleep, they weaken and are "cleaned," which prevents brain overload. Studies in mice have shown that after sleep, synapses decrease by approximately 20%. With sleep deprivation, the brain becomes overloaded with neural connections, which impairs the encoding of new information. In sleep-deprived rats, states of sleep were observed in specific cortical areas, despite the animal being awake.
Wakefulness Neurons
Neurons that maintain wakefulness (orexin and noradrenergic) can be damaged by chronic sleep deprivation. A 2014 study showed that after three days of simulated shift work, mice lost up to a quarter of neurons in the locus coeruleus.
Genetic Level
A 2013 study revealed that a week of sleep less than 6 hours alters the activity of 711 genes in blood cells, including genes related to the immune system, inflammation, metabolism, and stress response. The synchronization of genes with the circadian rhythm is disrupted. When the rhythm is disturbed, up to 97% of genes with daily expression lose it. Sleep deprivation activates the NF-κB system, which initiates inflammatory processes that, in chronic cases, can contribute to the development of cardiovascular, metabolic, and neurological diseases.
Telomeres and Aging
In individuals with chronic sleep deprivation and shift workers, telomeres (the ends of chromosomes, linked to aging) are shorter, indicating accelerated cellular aging.
Functional Impairments Caused by Sleep Deprivation
Attention and Reaction Time
After 17-20 hours of wakefulness, a person's reaction time is equivalent to being intoxicated with 0.5 permille of alcohol, and after 24 hours, it is around 1 permille. Drivers who sleep 4-5 hours are 4 times more likely to be involved in accidents, and those who sleep less than 4 hours are 11 times more likely.
Memory
Without sleep, the hippocampus records new information 40% worse. Sleep deprivation after learning impairs the transfer of information from short-term to long-term memory.
Emotional Sphere
After a sleepless night, the amygdala (the center of fear and anxiety) reacts 60% more strongly to negative stimuli, and its connection with the prefrontal cortex (responsible for rational thinking) weakens. This can lead to irritability, impulsivity, and emotional fluctuations. One sleepless night increases anxiety by approximately 30%.
Metabolism
Four hours of sleep over six nights reduces glucose tolerance to a level close to pre-diabetic. Ghrelin levels (the hunger hormone) increase by 28%, and leptin levels (the satiety hormone) decrease by 18%. This leads to an increase in food consumption by 300-500 kcal per day and cravings for sweet and salty foods.
Immune System
One night of sleep lasting 4 hours reduces the activity of natural killer cells (which destroy viruses and cancer cells) by approximately 70%. Sleep deprivation during vaccination halves antibody production.
Cardiovascular System
Sleeping less than 6 hours increases the risk of coronary heart disease by 48% and stroke by 15%. The transition to daylight saving time, associated with the loss of one hour of sleep, statistically correlates with an increase in heart attacks on the Monday after the transition.
Hormonal Balance
A week of sleeping 5 hours reduces testosterone levels in young men by 10-15%, which is equivalent to aging by 10-15 years. In women, the menstrual cycle and fertility can be disrupted.
Chronic Sleep Deprivation vs. Episodic
Chronic sleep deprivation (e.g., 6 hours of sleep for a month) is more dangerous than episodic. The body adapts to the new routine by altering metabolism and immune response, which often goes unnoticed.
Recovery from Sleep Deprivation
Weekend catch-up sleep does not fully restore insulin sensitivity and appetite. Waking up early, especially after a late bedtime, leads to a loss of REM sleep, which is concentrated in the early morning hours and is important for recovery.
Coffee, bright light, and stress can mask the symptoms of sleep deprivation but do not eliminate its negative consequences.
Recommendations for Minimizing the Effects of Sleep Deprivation
- Fixed Wake-Up Time: Set the same wake-up time daily, including weekends, with no more than a one-hour difference. Wake-up time is more important than bedtime.
- Bright Light in the Morning: Exposure to bright light within the first hour of waking helps synchronize circadian rhythms.
- Dim Light in the Evening: Soft, dim lighting in the evening promotes melatonin production.
- Limit Caffeine: Stop consuming coffee and energy drinks before 2:00 PM, considering caffeine's half-life (5-6 hours).
- Cool and Dark Bedroom: Maintain a bedroom temperature of 18-20°C and complete darkness.
- Avoid Alcohol as a Sleep Aid: Alcohol disrupts REM sleep and prevents full recovery.
- Regular Sleep: Instead of trying to "catch up" on sleep all at once, it is recommended to establish a regular sleep schedule of 8-9 hours over 1-2 weeks.
- Napping: Short naps (up to 20 minutes) before 3:00 PM can be beneficial.
Recovery from sleep deprivation is gradual and uneven. Attention and mood may improve within a few days, while metabolism recovers significantly more slowly.
Introduction: The Myth of the "Short Sleeper"
Many mistakenly believe that 6 hours of sleep is sufficient for them. Studies show that under such a regimen, performance drops to the level of two days without sleep, and the person does not feel severe fatigue because the brain stops signaling the problem. The norm for sleep is 7-9 hours; exceptions are rare genetic mutations.
- Many people believe that 6 hours of sleep is enough for them, and they feel perfectly fine.
- Hans Van Dongen's study (2003) showed that people who slept 6 hours for two weeks performed on attention and reaction tests at the level of those who had been awake for 48 hours.
- The subjective feeling of fatigue does not increase proportionally to actual sleep deprivation; the brain stops complaining.
- The normal duration of sleep for adults is 7-9 hours.
- Less than 7 hours of sleep is considered short sleep, and less than 6 hours is chronic sleep deprivation.
- "Short sleepers" are individuals with genetic mutations, making up a tiny fraction of the population.
- Most people who consider themselves "short sleepers" have simply become accustomed to sleep deprivation.
Signs of Sleep Deprivation
There are five key signs of sleep deprivation: dependence on an alarm clock, the need to catch up on sleep on weekends, instant sleep onset, drowsiness in calm environments, and a strong dependence on coffee. Accumulation of these signs is a reason to consider sleep problems.
- Need for an alarm clock: If you can't wake up without it or sleep significantly longer, it's a sign of sleep deprivation.
- Increased sleep duration on weekends: Sleeping 1.5-2 hours longer on weekends indicates sleep deprivation during weekdays.
- Falling asleep instantly: Falling asleep within 1-3 minutes of lying down indicates strong 'sleep pressure'. Normal is 10-20 minutes.
- Drowsiness in calm environments: Feeling drowsy during meetings, on transport, or while reading.
- Dependence on coffee: Inability to wake up and function normally without coffee.
Brain Impact: The Glymphatic System and Cellular Level
During sleep, the glymphatic system is activated, clearing the brain of toxins like beta-amyloid. Sleep deprivation disrupts this process. Adenosine accumulates at the cellular level, causing sleepiness, and caffeine only temporarily blocks its action.
- The brain's glymphatic system cleanses it of cellular waste products during sleep.
- During sleep, the interstitial space in the brain expands by 60%, enhancing the flow of cerebrospinal fluid that flushes out waste.
- Beta-amyloid, linked to Alzheimer's disease, is cleared twice as fast during sleep.
- Sleep deprivation impairs the glymphatic system's function, which may contribute to the accumulation of beta-amyloid and tau protein.
- Adenosine accumulates in the brain throughout the day and causes sleepiness; it is flushed out during sleep.
- Caffeine blocks adenosine receptors but does not eliminate adenosine, merely masking fatigue.
Effect on the Brain: Synapses and Neurons
Sleep deprivation leads to synapse overload, impairing the brain's ability to process information. Chronic sleep deprivation can also damage neurons responsible for wakefulness, as confirmed by animal studies.
- Synaptic Homeostasis Hypothesis: During wakefulness, synapses strengthen, and during sleep, they weaken and 'rest'.
- After sleep, synapses in mice became 20% smaller, and weak connections were removed.
- Without sleep, the brain becomes overloaded with neural connections, impairing the processing of new information.
- Sleep states were observed in individual cortical areas of wakeful rats.
- Neurons that maintain wakefulness (orexin and noradrenaline) can be damaged by chronic sleep deprivation.
- A study showed that after three days of simulated shift work, mice lost up to a quarter of the neurons in the locus coeruleus.
Impact on Genes and DNA
Sleep deprivation affects gene expression, disrupts circadian rhythms, and causes organ desynchronization. This activates inflammatory processes and accelerates telomere shortening, contributing to aging and disease development.
- A week of sleeping less than 6 hours led to changes in the activity of 711 genes in volunteers, including genes of the immune system, inflammation, and stress.
- Circadian rhythms are disrupted: genes start functioning at the wrong time.
- Organ desynchronization: the liver might think it's night when the brain thinks it's day.
- When rhythms are disrupted, up to 97% of genes with daily expression lose it.
- Sleep deprivation activates the NF-κB system, triggering inflammatory processes that, if chronic, can lead to various diseases.
- Telomeres, the ends of chromosomes associated with aging, are shorter in people with chronic sleep deprivation.
Impact on Cognitive Functions, Emotions, and Metabolism
Sleep deprivation reduces reaction time to the level of alcohol intoxication, increases the risk of accidents, and impairs memory and information consolidation. Anxiety increases, and reactions to negativity intensify. Glucose metabolism and hunger/satiety hormones are disrupted, leading to overeating.
- After 17-20 hours without sleep, reaction time slows to the level of 0.5 permille alcohol, and after 24 hours - to 1 permille.
- Drivers sleeping 4-5 hours are 4 times more likely to get into accidents; less than 4 hours - 11 times more likely.
- Without sleep, the hippocampus records new information worse (by 40%), and the transfer of information to long-term memory deteriorates.
- After a sleepless night, the amygdala (fear center) reacts to negative stimuli 60% stronger, and the connection with the prefrontal cortex weakens.
- One sleepless night increases anxiety by 30%.
- Four hours of sleep over six nights leads to a glucose tolerance level close to pre-diabetic.
- The hunger hormone ghrelin increases by 28%, and the satiety hormone leptin decreases by 18%, leading to increased calorie consumption and cravings for sweets/salty foods.
Impact on Immunity, Cardiovascular System, and Hormones
Sleep deprivation weakens immunity by reducing NK cell activity and antibody production. The risk of cardiovascular diseases (ischemic heart disease, stroke) increases. Testosterone levels decrease in men, and menstrual cycles and fertility are disrupted in women.
- One night of 4 hours of sleep reduces the activity of killer cells (NK cells) that destroy viruses and cancer cells by 70%.
- Sleep deprivation during vaccination halves antibody production.
- Sleeping less than 6 hours increases the risk of ischemic heart disease by 48% and stroke by 15%.
- The switch to daylight saving time (loss of 1 hour of sleep) is statistically linked to an increase in heart attacks.
- A week of sleeping 5 hours reduces testosterone in young men by 10-15%, equivalent to aging by 10-15 years.
- Women may experience menstrual cycle disturbances and reduced fertility.
Chronic Sleep Deprivation and Recovery
Chronic sleep deprivation is dangerous because the body adapts, masking the problem. Weekend recovery is incomplete, and early waking deprives you of valuable REM sleep. To minimize consequences, consistent sleep schedules, sleep hygiene (light, temperature, caffeine, alcohol), and sequential sleep recovery are important.
- Chronic sleep deprivation (e.g., a month of 6 hours of sleep) is more dangerous than episodic deprivation because the body adapts by altering metabolism and immune response, ceasing to signal the problem.
- Catching up on sleep on weekends does not fully restore insulin sensitivity and appetite.
- Waking up early shortens the REM sleep phase, which is most crucial for recovery and occurs in the morning hours.
- Coffee, bright light, and stress mask the symptoms of sleep deprivation but do not eliminate its consequences.
- To minimize the effects, a fixed wake-up time (difference no more than 1 hour), bright light in the morning, and dim light in the evening are important.
- Limiting caffeine after 2 PM, a cool (18-20°C) and dark bedroom improve sleep.
- Alcohol impairs REM sleep quality and recovery, despite seemingly aiding sleep onset.
- Recovery requires consistent sleep of 8-9 hours for 1-2 weeks or short naps (before 3 PM).
- Attention and mood recover in a few days, metabolism takes longer.