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Short Sleep – When is it Dangerous?


Saying that someone is a ‘short sleeper’ can be misleading because we don’t know whether it refers to someone who naturally needs little sleep or someone who is constantly sleep-deprived. This term is and can be used in both cases.

Here we talk about all short sleepers – those who thrive on less than 7 or 8 hours of sleep per night, and those who can get by with that time, but actually need a lot more. The first group makes up a tiny fraction of the general population, whereas the second and more numerous one is at risk of many mental and physical health problems due to a prolonged lack of sleep.

A useful vocabulary of short sleep

There are many ways to refer to short sleep, but here are some definitions that might be of help if you decide to research more about this topic:

  • short sleep – regular sleep of 6 hours or less;
  • sleep deprivation – shortening or absence of sleep;
  • partial sleep deprivation – shortening of sleep (used especially when we want to point out the difference between shortened sleep and no sleep – someone who suffers from any of these is called sleep-deprived);
  • sleep insufficiency / insufficient sleep syndrome – regularly not having enough sleep and suffering from negative consequences;
  • sleep loss – sleeping less than before;
  • sleep disturbance – any problem associated with impaired sleep duration and quality. Some examples include obstructive sleep apnea, insomnia, narcolepsy, and restless leg syndrome.
  • excessive daytime sleepiness – low concentration and energy paired with strong sleep inertia and sleepiness throughout the day. It is a symptom of many sleep disturbances as well as insufficient sleep.

Please note that not all short sleepers are sleep-deprived. There are some examples among the population of advanced age and, rarely, younger people, who are perfectly fine with short sleep.

Short sleep vs insufficient sleep

Short sleepers are people who normally sleep 6 hours or less per night. The National Sleep Foundation states that six hours ‘may be appropriate’ for some adults. This means that, for most of us, it is unacceptably low, but there is a small percentage of those who are naturally short sleepers.

If you feel you’ve had enough rest, are energetic and have a bright mind after sleeping for a short time, you might be one of the lucky short sleepers. In that case, you’ll suffer no mental or health deterioration as a consequence.

Unfortunately, many people are not ‘designed’ for such amount of sleep, but they can ‘get by’. They habitually sleep for about six hours and usually have a very tight daily schedule. Although they would personally tell you that they are getting enough sleep, this may be far from the truth. They might unknowingly accumulate sleep debt, which takes its toll in numerous ways.

There is a very simple way to test whether you sleep enough or not. People who have insufficient sleep tend to sleep longer when given the opportunity, whereas natural short sleepers just wake up feeling fresh, and their sleep time doesn’t vary on weekends and holidays. So, when you have free time, try to sleep in – if you wake up early and feel good, you might be a short sleeper, but if you sleep significantly longer, your body is catching up on sleep.

Sleep deprivation is a serious problem in the US, mostly affecting teenagers and working people. We should all think about our sleep habits because we might be a part of the sleep-deprived population without even realizing it.

Natural short sleepers – is the low need for sleep in their genes?

How much sleep we need is determined by a number of factors, such as sex, age, overall health, and genetics.

It seems that the very small percent of the population who are the actual, real short sleepers, can thank their genetics for not having to spend too much time ‘shut down’ and instead be more productive.

Scientists discovered a particular gene – DEC2 – that controls our circadian rhythm (internal biological clock). A mutation in this gene causes short sleep and high orexin secretion. Orexin is a hormone that promotes wakefulness. They also found that this kind of mutation doesn’t only affect sleep duration in humans, but also mice and even flies!

Symptoms of insufficient sleep syndrome

A person might be getting insufficient sleep if the following symptoms are present:

  • Excessive daytime sleepiness (but not suffering from any disorders that might cause it),
  • Habitually spending less than eight hours in bed,
  • A close person insists that the short sleeper needs to sleep a lot more (people around them notice fatigue, poor concentration, and irritability),
  • Weak immune system.

After given the chance to get more sleep, they will sleep a lot longer – which improves their symptoms.

Men are more likely to suffer from insufficient sleep than women, especially in their late thirties and as a result of work requirements – shifts, amount of work, or other factors. Perhaps young people put up with sleep deprivation well so the negative effects are not so obvious, but as a person ages, this behavior leaves more consequences.

Do not hesitate to ask for professional help should you have any of these symptoms – ignoring them is what aggravates the situation and leads to long-term health problems.

What are the dangers of short, insufficient sleep?

Those of us who have the average sleep needs, but sleep about six hours or less deprive themselves of all the benefits sleep offers. There are numerous consequences, from the seemingly less problematic ones, like being prone to the common cold, to more serious drowsy driving and high risk of cardiovascular disease.

Remember that chronic sleep insufficiency leads to chronic health problems. So, what are the exact consequences?

  • Mood disorders. Sleep ensures a healthy flow of neurotransmitters and hormones. When we don’t sleep enough, these valuable chemicals are imbalanced, which reflects on our mood. We become irritable, anxious, our stress-coping mechanism doesn’t help us relieve stress and our stress hormones are increased. In the long run, we might develop anxiety or depression.
  • Poor cognitive abilities. As our brain doesn’t get rested nor memory consolidated, we find it difficult to learn, remember or even notice things around us. With poor attention, we become poor performers and dangerous drivers.
  • Weight gain and obesity. Scientists keep warning about the inability of our body to deal with food properly after sleep deprivation. To top off this problem, many tend to eat more both during the day and late at night, perhaps trying to make up for the lost energy. Also, a lack of sleep is associated with hormonal problems – there’s an increase in our ‘hungry hormone’ ghrelin and a decrease in the ‘I’m full’ hormone – leptin. Another problem is insulin, the glucose regulator. Its levels get too high after a meal, which is associated with weight increase. This is not the only thing that leads to a weight increase, it’s also a lack of exercise (people who don’t sleep enough usually have no energy or strength to exercise).
  • Diabetes. The change in the insulin levels and insulin resistance in cells throughout the body after only one night of sleep restriction is huge. After several nights of shortened sleep, the insulin resistance in fat cells is 30% higher, whereas blood sugar level rises for about 16%. Those are levels seen in people who suffer from diabetes – shortened sleep leads to a prediabetic state.
  • Hypertension, heart disease. While we sleep, our heart rate slows down and blood pressure decreases. But after one night of poor sleep, blood pressure gets significantly higher and remains so throughout the day. If this continues for a prolonged period of time, it could cause chronic problems with hypertension and even heart disease as a consequence.
  • Restoration and the immune system. Human growth hormone is released in sleep, and while it ensures that kids grow, it helps adults restore cells and tissues. Our immune system also greatly benefits from sleep. Sleep deprived individuals have problems with healing and defending from various illnesses.

Additional resources:

  1. Grandner M. A, Patel N. P, et al. Problems Associated with Short Sleep: Bridging the Gap between Laboratory and Epidemiological Studies. Sleep medicine reviews. November 6, 2009. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2888649/ Accessed February 9, 2019.
  2. He Y, Jones C. R, et al. The Transcriptional Repressor DEC2 Regulates Sleep Length in Mammals. Science. 14 August 2009.  http://science.sciencemag.org/content/325/5942/866  Accessed February 9, 2019.
  3. Hirano A, Hsu P. K, et al. DEC2 modulates orexin expression and regulates sleep. PNAS. March 27, 2018.  https://www.pnas.org/content/115/13/3434.short?rss=1  Accessed February 9, 2019.
  4. Insufficient Sleep Syndrome – Overview & Facts. Sleep education. http://sleepeducation.org/sleep-disorders-by-category/hypersomnias/insufficient-sleep-syndrome  Accessed February 9, 2019.
  5. Sleep and Disease Risk. Healthy Sleep. Harvard. http://healthysleep.med.harvard.edu/healthy/matters/consequences/sleep-and-disease-risk  Accessed February 9, 2019.

The information on this website is not intended to replace a one-on-one relationship with a qualified health care professional and is not intended as medical advice. Read our full medical disclaimer.

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