This infographic advert describes the sleeping habits of a few well-known people:

People who need little sleep

A few of them were claimed to have gotten by with extremely little sleep. For example: Tesla, 2 hours of sleep per day.

Is it true that some people can function normally on just 2 hours sleep per day, over the long term?

  • I initially thought the claim was "Are there some people really survive only a few hours sleep per night?", but then I say that you thought that was well-documented, so I changed to it ask about Tesla in particular. Otherwise, what is the actual question? – Oddthinking Dec 26 '16 at 4:57
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    @Oddthinking Yes, so Tesla is the well known case about whom the 2 hour claim is made, but one can generalize it to ask about verified cases of people who need a lot less than 4 hours of sleep. This is because it is well know that there are people who only need 4 hours of sleep on the long term but I don't think there are verified cases about people who need just 2 hours. So, this raises some questions about Tesla's case. But I could be wrong about there not being known cases of people who need 2 hours sleep... – Count Iblis Dec 26 '16 at 5:04
  • So you would prefer the question to be "Can anyone function on 2 hours sleep per day?" – Oddthinking Dec 26 '16 at 5:05
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    @Oddthinking "Is it true that some people can function normally on just 2 hours sleep per day, over the long term?" sounds good to me, thanks! – Count Iblis Dec 26 '16 at 5:07
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    Comment only as this does not tackle the question of 2h-sleepers. But this paper ncbi.nlm.nih.gov/pmc/articles/PMC2140008 suggests that the income-rich tend to have more sleep than the income-poor. So not quite the same as the poster title suggests. – anonymized Dec 26 '16 at 19:10

Short version:

A short-sleep human phenotype has been described in the literature. However, the reported sleep times I found in the scientific literature for those people are around 6h / day vs. 8h for controls, so nowhere near 2 h.

About Tesla: The Wiki page has a paragraph on his sleeping habits where biographies are cited that he claimed to never sleep more than 2h - but also that he spoke of dozing to "recharge his batteries". (Unfortunately, I don't have access to these books). However, see also below.

Long version:

First of all, I'd like to caution that self-reported sleep times and functionality are not very trustworthy:

  • People who experience microsleeps often remain unaware of them, instead believing themselves to have been awake the whole time, or to have temporarily lost focus.
    --- Wiki page on microsleep.

  • It is well established that sustained wakefulness and the resulting cumulative sleep debt increase the likelihood that personnel will briefly (and uncontrollably) nod off on the job, even during flights (Dinges, 1995).
    The longer someone remains awake, the more likely these involuntary sleep lapses become. In addition, sleepiness takes a heavy toll on reaction time, motivation, attention, memory, endurance, and judgment (Krueger, 1989).
    Naitoh and Kelly (1993) warn that sleep deprivation in extended operations quickly leads to motivational decrements, impairedattention, short-term memory loss, carelessness, reduced physical endurance, degraded verbal communication skills, and impaired judgment.
    ---Caldwell: "An Overview of the Utility of Stimulants as a Fatigue Countermeasure for Aviators"

This is the closest I found so far:

  • It is well known that the amount of sleep needed varies between individuals.

    Sleep need is different for everyone. Some people require more sleep than others, ranging from 5.5 to 9 hours a day for people age 30 to 50 years. However, the majority require an average of 7 to 8 hours of daily sleep. ---Fatigue Management Guide for Canadian Marine Pilots

  • There's a mother and daughter that are famous for being short sleepers, and a gene variant for short-sleep phenotype was identified with them:

    The habitual self-reported total sleep time per 24-hour day was much shorter in mutation carriers (average 6.25 hours) compared with the noncarriers (average 8.06 hours) in this family.
    --- The Transcriptional Repressor DEC2 Regulates Sleep Length in Mammals, Science 2009, Vol. 325, Issue 5942, pp. 866-870

  • There are a number of mutations of BHLHE41. Mutations reduce total sleep while maintaining NREM sleep and provide resistance to the effects of sleep loss.SLEEP, Vol. 37, No. 8, 1327 - 1336C, 2014

    The study looks at a number of mutations that seem to affect sleep duration as well as the need for sleep. So there are people who just need much less sleep than others. However, again the measured daily amount of sleep for the shortest sleeper group is 6 h, so nowhere near the 2h claims of the poster. However, the study also looked at the effect of chronic sleep deprivation at a level of 4h sleep per day over 5 days. Under these circumstances, the natural short sleepers did better in the vigilance tests (however, the paper also says that the particular test results are anyways known to be heritable to a large degree - and if I understand their table correctly, in all groups the sleep deprived "lapses" are roughly twice as much as the baseline performance. But the short sleepers had far less of them in absolute numbers).

I had a look at military studies assuming that they'd look carefully how to make soldiers function with lowest possible amount of sleep. I did not find evidence that they select soldiers for the ability to cope with low amounts of sleep. In contrast, I found that they try hard not to get too much below 8h/day because of the functional impairments:

  • The USAF report by Calwell has a diagram on page 5 giving the prediction of soldier's "effectiveness" in a military campain over a few days including 3 2h naps (within 24 h):USAF model sleep deprivation It concludes:

    Remember, proper sleep is the only sure way to keep fatigue in check!
    If a full 8-hours of sleep is impossible, naps are a good compromise, each individual nap should be long enough to provide at least 45 continuous minutes of sleep, although longer naps (2 houre) are better. In general, the shorter each individual nap is, the more frequent the naps should be (the objective remains to acquire a daily total of 8 hours of sleep).

    (Emphasis original) It should be noted that the report also says "In particular, being physically fit apparently offers no benefit for sustaining mental alertness." Thus unfortunately there is no indication here that the military even considers selecting their soldiers according to their ability to function without sleep.

  • Minimum Sleep Requirement
    Researchers have tried to determine the minimum amount of sleep required to maintain performance. According to many sleep researchers the minimum during each 24-hour period (“day”) is between 4.5 and 5.5 hours of continuous sleep. If you usually sleep between 7 to 8 hours per night, you may function adequately for a few days with this minimal amount of sleep. However this cannot be sustained for an extended period of time. If you get less than your required sleep for three or more consecutive days, you may perform as poorly as though you were legally drunk. Such tasks as driving, piloting, or operating dangerous equipment require that you be alert. Under extreme circumstances where sleep cannot be achieved continuously, research on napping shows that 10- to 20-minute naps at regular intervals during the day can help relieve some of the sleep deprivation and thus maintain minimum levels of performance for several days. However, researchers caution that levels of performance achieved using ultrashort sleep (short naps) to temporarily replace normal sleep, are always well below that achieved when fully rested. It is, however, better than having no sleep!
    ---Fatigue Management Guide for Canadian Marine Pilots

Bits and pieces wrt. to rich & famous people's sleep habits:

  • Unfortunately, like in the related question Did Albert Einstein sleep 10-11 hours daily?, I found tons of varying claims - but no reliable sources.

  • However, the short sleeper claims do vary quite a bit even for the same famous person: taking Tesla as an example as he was topic of the original question, the 2h number appears often. However, the poster in the question omits the dozing, and this web page says "After a short stint under Edison's umbrella, Nikola Tesla became a bitter rival of his former mentor. We have all heard of the "war of the currents", but Edison and Tesla clashed in another battlefield. They tried to outbid each other in sleeping little. Tesla noted that Edison slept much more than he would want others to believe. That injects a dose of boastful personality to their own reports on how much the great inventors slept. Tesla who could indeed work throughout the night, would often crash for the entire day of sleep after his exploits. He exhibited classic signs of manic creativity, which might have been interrupted by short recuperative naps or long recovery sleep. Otherwise, Tesla was nothing more than a short sleeper."

  • Also this blog post does not give a proper source: However, Edison's assistant is said to have hinted that Edison in fact slept more than he admitted. And "he often got in a couple of 3 hour naps during the day" - which is much more than the poster in the question states.

  • While not giving proper sources, here's a description of someone trying to find evidence for the polyphasic sleep pattern attributed to Leonardo da Vinci:

    Leonardo's polyphasic sleep is probably an urban myth. I could not locate any credible sources with any notes on his sleep habits, and yet da Vinci is nearly always mentioned whenever the art of napping comes into question. It seems quite strange that someone would come up with a crazy polyphasic schedule idea at the time of leisurely Renaissance life that was well-timed by the superiority of sunlight over candlelight. Allegedly, hinting at a monophasic mindset, he spoke of death: "As a well-spent day brings happy sleep, so a life well used brings happy death". Even more telling is Bandello's report on da Vinci's work over "The Last Supper". Leonardo would work continuously from dawn to dusk forgetting about food and drink. Stunned Bandello would definitely reported the round-the-clock work of a polyphasic sleeper as even more amazing.

  • Not a very scholarly source, but at least a name attached:

    "There are some people who need very little [sleep], and there are some people that need more than the average," explains Dr. Vicky Seelall, the director of the Sleep Health Center at Beth Israel Medical Center.
    "Five percent of the population goes down to four hours a night or even less at times," says Seelall, "and there's about 5% that will need somewhere between 10 and 12 hours of sleep a night. "I have one patient that only sleeps two hours a night, and he's completely fine."
    --- http://www.nydailynews.com/history-greatest-figures-owe-success-sleeping-article-1.412799

  • Excellent answer. Since you mention soldiers, every soldier I know (USA) told me about how they were intentionally deprived of sleep while in basic training. One man told me he didn't get sleep for 4 days straight. This stress of course is intentional, but they may have accumulated some data on it. – fredsbend Dec 27 '16 at 2:58
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    @fredsbend: Yes - I guess the USAF report model/diagram was built using such data. It also cites: "Angus and Heslegrave (1985) found that cognitive abilities suffer 30 percent reductions after only 1 night without sleep and 60 percent reductions after a second night. Belenky et al. (1994) estimates a 25 percent decline in the ability of personnel to perform useful mental work with each 24-hour period of sleep loss. In a Norwegian military field study, Roussel (1995) found that the fighting capability of soldiers was reduced by 80 percent across 4 consecutive days of sleep deprivation." – anonymized Dec 28 '16 at 10:16
  • I suspect that a goal of training is to improve those numbers, and they deprive them of sleep to test how well the training sticks. – fredsbend Dec 28 '16 at 15:34
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    @fredsbend: That may be so. However, in that case the training doesn't seem to achieve much in general if both USAF report and Canadian pilot handbook still emphasize that good performance over longer periods of time can be gotten only with appropriate amounts of sleep in the order magnitude of 8h per day. (at least compared to, say, what the physical fitness training can achieve compared to say the average office worker). I didn't even see indication like "general public needs 8 h, pilots are required to pass test at 6 h", i.e. that they select soldiers accordingly (but they may not tell). – anonymized Dec 28 '16 at 17:06

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