If you usually get less than seven hours of sleep, you are probably a short sleeper. Many people are short sleepers due to lifestyle choices. For example, juggling work, recreation, and family responsibilities may not leave enough hours in the day to get the recommended amount of sleep each night.
But it’s not just the number of hours we spend asleep. It’s also the quality of your sleep that matters. Some people do not spend enough time in deep sleep. So, even if they get seven hours of sleep, it may not be good quality and restorative sleep they need.
If you are a short sleeper or do not get enough deep sleep, you might feel tired the next day and lack energy, which can affect your day to day activities.
Sleep occurs in two main phases, which include non-rapid eye movement and rapid eye movement sleep. Non-rapid eye movement (NREM) sleep accounts for about 80 percent of the time you spend asleep. During that time, you cycle through a few stages of NREM from light sleep to deep sleep. Deep sleep is also called slow-wave sleep. The brain waves during this stage of slep are low frequency.
During slow-wave sleep, your heart and respiratory rate are low. It is considered the deepest stage of sleep and the most difficult to arouse from. It’s also a critical phase of the sleep cycle.
Getting enough slow-wave sleep is important for a variety of reasons. During slow-wave sleep, your body repairs itself. The immune system is strengthened, muscles and tissues regenerate, and energy is restored. Studies have also shown that getting enough slow-wave sleep has a positive effect on learning capacity and memory. (1)
Even if you get an adequate number of hours of sleep, but do not spend enough time in slow-wave sleep, you will likely feel the effects. Spending enough time in slow-wave sleep affects your memory, energy, and ability to learn. Daytime alertness is also affected by slow-wave sleep. (2)
Researchers still don’t know everything about sleep. But we do know that a lot happens during the slow-wave phase. For example, along with repairing the body and restoring energy, slow-wave sleep helps sort out new connections in the brain.
We all take in a lot of information daily. The information you are bombarded with each day leads to new neural connections in the brain to store the data.
Sounds useful right? It can be. We need some of those connections to consolidate memories and learn. But we don’t need all new connections to remain permanent. Remember, there is a massive amount of information. If all the connections were permanent, your brain would become overloaded with information.
Your body has a way of dealing with all the unneeded connections. When you are in slow-wave sleep, your brain does a little housekeeping and gets rid of unnecessary connections.
Getting rid of unneeded connections help improve your alertness the next day. If you do not get enough slow-wave sleep, your brain does not sort through and get rid of the unneeded connections as effectively.
It’s clear that getting enough slow-wave sleep is essential for your well-being. But it’s not just the amount of time you spend in slow-wave sleep. It’s also the strength of the waves. Research has found that it’s the strength and length of slow waves that play a role in restorative sleep.
In the past, medications have been studied to improve slow- wave sleep. But the drugs failed to boost memory consolidation. Plus, as with most medications, the possibility of side effects was also an issue.
Fortunately, technology is now developed that can improve slow wave sleep. Clinical studies have indicated that specific sounds enhance the strength of the slow waves during sleep.
A study from the University of Utah published in Brain and Behavior has noted that there are neural connection patterns in the brains of short sleepers that suggest some of them may actually be getting enough sleep, but may also be more tired than they realize.
Habitual short sleepers are those who can sleep far less than the recommended amount without experiencing any daytime symptoms. (3)
Dr. Jeff Anderson, co-author of the study, noted that the evidence helps them understand why some people do not seem to need much sleep. He suggested that it is possible some brains can actually do the “restorations” done in sleep throughout the day while awake.
Sleep is one of the most essential functions of our body, though researchers are still unable to say exactly why that is, which makes it such an active field of research. (4)
For the most part, scientists believe that sleep helps clear the brain of clutter thoughts that have accumulated throughout the day, and it allows for essential pieces of information to be stored in short or long-term memory centers.
Most people who get less than 7-9 hours of sleep have daytime symptoms like irritability, fatigue, and inability to concentrate. There are a host of physical and mental health problems associated with chronic short sleep durations, including heart disease, mood disturbance, obesity, decline in cognition, and increased mortality risk. This is not to mention the increased risk of accidents due to tiredness.
Interestingly, some can sleep six or less hours a night and report no ill effects. In a study done in 2009, University of Utah neurologist, Chris Jones, along with his colleagues, found genetic mutations associated with short sleep duration. The genetic factors found in this study suggest that those who can function properly on six hours or less of sleep may feel fine, but actually have “tiredness” in the mind and organs.
To answer the questions about how short sleepers can function without side effects, researchers looked at brain wire mapping. Their goal was to figure out the connections of neurons underneath the sheath of brain cells. The idea was to figure out how the connections are related to functionality with and without sleep.
The Human Connectome Project is a multi-university consortium that is analyzing these brain connections in 1200 people. They are using MRI scans. So far, data for 900 patients have been released, which allowed the University of Utah researchers to analyze the brain connectivity.
The data was split into two groups: Those who reported normal sleep duration and those who reported six hours or less a night over the last month. The short sleepers were divided again into two groups: Those who had daytime symptoms and those who did not.
Both short sleeper groups had connectivity patterns on MRI that were more associated to sleep than wakefulness. People were instructed to stay awake while in the MRI; however, Dr. Anderson noted that short sleepers often drifted off while lying there in the scanner. That includes even the people who reported no daytime dysfunction.
One hypothesis about short sleepers who deny daytime dysfunction is that their awake brain systems are in overdrive. This suggests that while lying still and bored in an MRI scanner, they had nothing else to do than fall asleep. There are several public safety implications in this hypothesis, because there are other “boring” activities like driving and operating a machine by rote memory that could lead to injury or accident.
Short sleepers who denied dysfunction showed increased connectivity between the cortexes that process sensory information and the hippocampus, which is responsible for memory. Those short sleepers who fell asleep in the MRI scanner may have been performing memory consolidation, which is not something non-short sleepers can do. This is indicative of short sleepers being able to do memory consolidation that is usually done during sleep while they are awake, reducing their need for sleep. They could also be falling asleep during the day without even realizing it. Short Sleepers Are At Risk For Heart Disease.
As with all new findings, further research is necessary to test the hypothesis. The next part of the research that the University of Utah team will focus on is whether short sleepers without daytime dysfunction are actually doing well clinically.
In the next study, researchers will find people who sleep six hours or less naturally, regardless of the day or whether they are on vacation. They will perform brain imaging and examine cognitive performance like driving simulator testing, which will give them objective information about how they are truly performing.
Insufficient sleep may also be affecting their ability to perceive any daytime sleepiness. The research team is particularly interested in understanding the perceived symptoms or lack thereof in short sleepers. This may vary from the symptoms of long sleepers.
The analysis of the connectome data showed the team in Utah that self-reporting sleep duration played a role in the variation between resting connectivity profiles. Further functional MRI studies should take that and the actual sleep duration into account while interpreting results.
The researchers are hopeful that this ongoing research will answer the key questions about why each person needs a different amount of sleep.
© 2021 American Sleep Association.