At the Centre for Sleep Research in South Australia, researchers deprived volunteers of sleep for 24 hours. Subsequent mental performance was equivalent to a blood alcohol level of 0.10%. For perspective, a level of 0.08% is legally impaired and most people pass out at 0.15%. Another study found that most sleep-deprived people didn’t realize they were cognitively impaired.
Sleep is an investment in the energy you need to be effective tomorrow.
Importance of sleep
In addition to clear thinking, sleep has amazing benefits:
70% less likely to catch a cold
40% faster reaction times
35% lower stress hormones
20% of serious highway accidents are caused by driver fatigue
15% higher testosterone for men
10% lower risk of diabetes
A well-spent day brings happy sleep.
-Leonardo da Vinci
How to sleep well
Sleep 7–9 hours every night
Avoid screen time at least 1 hour before bed because blue light interferes with sleep
At night, set your room temperature to 66–70°F/19–21°C to trigger sleep
Go to bed and wake up at the same time to maintain your circadian rhythm
Do not sleep in on weekends and holidays
When you wake up, expose your eyes to bright sunlight to reset melatonin levels
Melatonin is a hormone that rises when it’s dark and signals your body to sleep
During seasons when it’s dark in the morning, shine a 10,000-lux bright light lamp on your closed eyes for 60 seconds
Early to bed and early to rise makes a man healthy, wealthy, and wise.
How to start today
Set a recurring bedtime alarm
Set a recurring wakeup alarm for 8 hours later
Follow the instructions above for sleeping well
It takes 1–2 days to adjust to a new sleep schedule
Life-hack: When in bed, meditate. Either you will have a deep meditation or fall asleep. Victory either way.
About 35% of Americans do not get enough sleep. When I was sleep deprived during medical school, I was irritable and impatient. And when I was sleep training my kids, my work performance suffered. Now, I have a personal rule that I sleep on major decisions.
In the end, winning is sleeping better.
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48 participants slept 4, 6, or 8 hours/night for 14 days, or zero hours for 3 days
Sleeping 4 or 6 hours/night resulted in cumulative dose-dependent deficits in cognitive performance (equivalent to 2 nights of total sleep deprivation)
Participants were largely unaware of deficits, which may explain why some people think sleep deprivation has minimal consequences
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19 participants were injected with Hepatitis A vaccine
One group had a regular night’s sleep while the other group did not sleep for 24 hours
4 weeks later, the group who slept had produced nearly twice the antibodies
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66 participants slept 3, 5, 7, or 9 hours/day for 7 days
Participants with 3 hours of sleep had 40% slower reaction times compared to those with 9 hours of sleep
Walker MP et al. (2002). Practice with sleep makes perfect: sleep-dependent motor skill learning. Neuron. 35(1): 205–211.
62 participants were trained on a finger tapping task
A night of sleep improved motor speed performance by 20% without loss of accuracy, compared to same period of time spent awake
Taffinder NJ et al. (1998). Effect of sleep deprivation on surgeons’ dexterity on laparoscopy simulator. Lancet. 352(9135): 1191.
Leproult R et al. (1997). Sleep loss results in an elevation of cortisol levels the next evening. Sleep. 20(10): 865–870.
de Mello MT et al. (2013). Sleep disorders as a cause of motor vehicle collisions. Int J Prev Med. 4(3): 246–257.
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Shan Z et al. (2015). Sleep duration and risk of type 2 diabetes: a meta-analysis of prospective studies. Diabetes Care. 38(3): 529–537.
A meta-analysis of 10 studies with 482,502 participants found that sleeping 7–8 hours/day was associated with lowest risk of type 2 diabetes
Risk was higher with sleep deprivation of 1 hour/day (6%) or >2 hours (37%)
Risk was also higher for sleeping an extra 1 hour/day (11%) or >2 hours (40%)
Leproult R, Van Cauter E. (2010). Role of sleep and sleep loss in hormonal release and metabolism. Endocr Dev. 17: 11–21.
Sleep deprivation results in decreased glucose tolerance, decreased insulin sensitivity, higher evening concentrations of cortisol (stress hormone), higher levels of ghrelin (hunger hormone), decreased levels of leptin (satiety hormone), and increased hunger and appetite
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66 participants were trained on a puzzle with a hidden shortcut
Those who got 8 hours of sleep after training were more than twice as likely to see the shortcut compared to those who stayed awake for 8 hours (59.1% vs. 22.7%)
Lim J, Dinges DF. (2010). A meta-analysis of the impact of short-term sleep deprivation on cognitive variables. Psychol Bull. 136(3): 375–389.
A meta-analysis of 70 studies found that short-term sleep deprivation impaired simple attention (effect size = 0.73–0.76), complex attention (effect size = 0.31–0.48), processing speed (effect size = 0.25–0.30), working memory (effect size = 0.52–0.56), and short-term memory (effect size = 0.38)
Philibert I. (2005). Sleep loss and performance in residents and nonphysicians: a meta-analytic examination. Sleep. 28(11): 1392–1402.
A meta-analysis of 60 studies with 959 doctors and 1,028 non-doctors found that sleep deprivation impaired performance (effect size = 0.95)
Sleep deprivation impaired clinical performance (effect size = 1.54), vigilance (effect size = 1.33), memory (effect size = 0.81), and cognitive performance (effect size = 0.56)
For doctors, sleep deprivation of 24–30 hours impaired aggregate cognitive and clinical performance (effect size = 0.99), which was equivalent to going from the 50th percentile to the 15th
Similarly, the decrease in clinical performance (effect size = 1.54) was equivalent to going from the 50th percentile to the 7th
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133 participants were trained on a visual discrimination task
When participants were deprived of sleep for 30 hours after training, then tested after 2 full nights of recovery sleep, they showed no significant improvement despite normal levels of alertness
This demonstrated that sleep within 30 hours of training was absolutely required for improved performance
Wagner DT et al. (2012). Lost sleep and cyberloafing: Evidence from the laboratory and a daylight saving time quasi-experiment. J Appl Psychol. 97(5): 1068–1076.
On the Monday following the switch to Daylight Savings Time (DST), Google users searched for 3.1% more entertainment-related websites
In a study of 96 students, 1 hour of disturbed sleep the previous night resulted in 20% more cyberloafing
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A prospective cohort study of 2,737 interns found that working overnight increased risk of needlestick injuries by 61%
Nighttime work increased risk by 104% vs. daytime work
Landrigan CP et al. (2004). Effect of reducing interns’ work hours on serious medical errors in intensive care units. N Engl J Med. 351(18): 1838–1848.
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How to sleep well
Hirshkowitz M et al. (2015). National Sleep Foundation’s sleep time duration recommendations: methodology and results summary. Sleep Health. 1: 40–43.
Chang AM et al. (2015). Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proc Natl Acad Sci USA. 112(4): 1232–1237.
Green A et al. (2017). Evening light exposure to computer screens disrupts human sleep, biological rhythms, and attention abilities. Chronobiol Int. 34(7): 855–865.
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People living in preindustrial societies in Tanzania, Namibia, and Bolivia sleep an average of 6.9–8.5 hours per night (5.7–7.1 hours of actual sleep time)
Sleep onset is 3.3 hours after sunset
Sleep occurs during nightly period of falling temperature
Light exposure is maximal in the morning
Harding EC, Franks NP, Wisden W. (2019). The temperature dependence of sleep. Front Neurosci. 13: 336.
Prior to sleeping, melatonin levels rise and core body temperature declines
Optimal room temperature is 19–21°C
Sleep is disturbed when the environment is too cold, or too hot and humid
Potter GDM et al. (2016). Circadian rhythm and sleep disruption: Causes, metabolic consequences and countermeasures. Endocr Rev. 37(6): 584–608.
Humans have a circadian rhythm with a period of about 24 hours
“Social jetlag” refers to different bedtimes on work days and non-work days, and it is associated with obesity and insulin resistance
Wong PM et al. (2015). Social jetlag, chronotype, and cardiometabolic risk. J Clin Endocrinol Metab. 100(12): 4612–4620.
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Blood levels of melatonin are high at night and low during the day
Melatonin secretion is reduced by exposure to light
Melatonin induces drowsiness and sleep
Magnusson A, Kristbjarnarson H. (1991). Treatment of seasonal affective disorder with high-intensity light. J Affect Disord. 21(2): 141–147.
How to start today
Sack RL. (2010). Jet lag. N Engl J Med. 362(5): 440–447.
Liu Y et al. (2016). Prevalence of healthy sleep duration among adults–United States, 2014. MMWR Morb Mortal Wkly Rep. 65(6): 137–41.
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