Good sleep

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.

-Thomas Roth

Importance of sleep

In addition to clear thinking, sleep has amazing benefits:

Healthier

• 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

Smarter

• 100% more creative insights

• 30% better attention

• 20% better memory

• You must sleep within 30 hours of learning or you won’t improve at all

Happier

• 30% lower risk of depression

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.

-Benjamin Franklin

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.

-Naval Ravikant

Personal notes

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.

-Jodie Foster

References

Dawson D, Reid K. (1997). Fatigue, alcohol and performance impairment. Nature. 388(6639): 235.

• In a study of 40 subjects, 24 hours of sustained wakefulness was equivalent to a blood alcohol concentration of 0.10% for cognitive psychomotor performance (legal limit for driving is 0.08%)

Van Dongen HP et al. (2003). The cumulative cost of additional wakefulness: dose-response effects on neurobehavioral functions and sleep physiology from chronic sleep restriction and total sleep deprivation. Sleep. 26(2): 117–126.

• 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

Healthier

Cohen S et al. (2009). Sleep habits and susceptibility to the common cold. Arch Intern Med. 169(1): 62–67.

• A study of 153 participants found that those who averaged <7 hours of sleep over the past 14 days were 2.9X more likely to develop a cold after being deliberately infected with rhinovirus, compared with those who averaged >8 hours of sleep

Lange T et al. (2003). Sleep enhances the human antibody response to hepatitis A vaccination. Psychosom Med. 65(5): 831–835.

• 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

Griffith CD, Mahadevan S. (2006). Sleep deprivation effect on human performance: A meta-analysis approach. Idaho National Laboratory.

• A meta-analysis of 7 studies found that sleep deprivation impaired reaction speed (effect size = 0.84), reaction time (effect size = 0.63), and accuracy (effect size = 0.27)

Belenky G et al. (2003). Patterns of performance degradation and restoration during sleep restriction and subsequent recovery: a sleep dose-response study. J Sleep Res. 12(1): 1–12.

• 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.

• A study of 6 surgeons found that those who had been awake all night made 20% more errors with a laparoscopic simulator and took 14% longer to complete tasks, compared to those who had a full night of sleep

Leproult R et al. (1997). Sleep loss results in an elevation of cortisol levels the next evening. Sleep. 20(10): 865–870.

• A study of 33 men found that sleeping for 4 hours instead of 8 increased stress cortisol levels by 37% the next day

de Mello MT et al. (2013). Sleep disorders as a cause of motor vehicle collisions. Int J Prev Med. 4(3): 246–257.

• Driver fatigue is linked to 16–20% of serious highway accidents

Leproult R, Van Cauter E. (2011). Effect of 1 week of sleep restriction on testosterone levels in young healthy men. JAMA. 305(21): 2173–2174.

• 10 young men restricted sleep to 5 hours/night for 1 week, and this caused testosterone levels to decrease by 10–15%

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

Spiegel K, Leproult R, Van Cauter E. (1999). Impact of sleep debt on metabolic and endocrine function. Lancet. 354(9188): 1435–1439.

• 11 young men restricted sleep to 4 hours/night for 6 nights, and this lowered glucose tolerance by 30–40%

Smarter

Wagner U et al. (2004). Sleep inspires insight. Nature. 427(6972): 352–355.

• 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

Stickgold R, James L, Hobson JA. (2000). Visual discrimination learning requires sleep after training. Nat Neurosci. 3(12): 1237–1238.

• 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

Ayas NT et al. (2006). Extended work duration and the risk of self-reported percutaneous injuries in interns. JAMA. 296(9): 1055–1062.

• 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.

• A prospective randomized study of 2,203 patient-days involving 634 admissions found that medical interns made 35.9% more serious medical errors when on call for ≥24 hours every third night vs. not being on call

Happier

Zhai L, Zhang H, Zhang D. (2015). Sleep duration and depression among adults: A meta-analysis of prospective studies. Depress Anxiety. 32(9): 664–670.

• A meta-analysis of 7 studies with 25,271 participants found that less sleep increased risk of depression by 31%

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.

• The National Sleep Foundation recommends that adults aged 18 to 64 get 7–9 hours of sleep per night

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.

• 12 participants who read a blue-light-emitting eBook vs. a print book for 4 hours before bedtime for 5 evenings had 55% lower levels of melatonin; took 10 minutes longer to fall asleep; had 10% less rapid eye movement (REM) sleep; and took hours longer to feel fully alert the next morning

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.

• 19 participants were exposed to blue light from computer screens from 9 to 11 p.m., and this decreased average sleep time by 16 minutes; reduced production of melatonin; and increased night awakenings

Hale L et al. (2018). Youth screen media habits and sleep: sleep-friendly screen-behavior recommendations for clinicians, educators, and parents. Child Adolesc Psychiatr Clin N Am. 27(2): 229–245.

• The American Academy of Pediatrics (AAP) and American Academy of Sleep Medicine (AASM) recommend that children’s screens be turned off at least 30 minutes before bedtime

Yetish G et al. (2015). Natural sleep and its seasonal variations in three pre-industrial societies. Curr Biol. 25(21): 2862–2868.

• 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.

• A study of 447 participants found that “social jetlag” was associated with higher triglycerides, insulin resistance, and obesity

Zhdanova IV et al. (1998). Endogenous melatonin levels and the fate of exogenous melatonin: Age effects. J Gerontol A Biol Sci Med Sci. 53(4): B293–298.

• Melatonin levels start rising around 9 p.m. and drop to low levels around 7–9 a.m.

Brown GM. (1994). Light, melatonin and the sleep-wake cycle. J Psychiatry Neurosci. 19(5): 345–353.

• 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.

• 10 patients with seasonal affectivity disorder (SAD) received 40-minute exposure to 10,000-lux white light for 8 days, and this improved SAD ratings from 22.6 before to 6.4 after

How to start today

Sack RL. (2010). Jet lag. N Engl J Med. 362(5): 440–447.

• The circadian clock resets an average of 92 minutes later each day after a westward flight, and 57 minutes earlier after an eastward flight

Personal notes

Liu Y et al. (2016). Prevalence of healthy sleep duration among adults–United States, 2014. MMWR Morb Mortal Wkly Rep. 65(6): 137–41.

• A study of 444,306 adults found that 65.2% slept at least 7 hours per night

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