Sleep: Everything You Wanted To Know, But Were Too Tired To Ask

There’s something that is more important for health than diet, exercise and social connections. Sleep. We all know it as we clearly feel the effects of inadequate sleep (bad eating, impaired thinking, constant colds) and the science is clear.

I read an excellent book on the topic, “Why We Sleep” by Matthew Walker, which spurred me to research the topic more deeply. I was fortunate then to meet one the world’s leading experts on sleep, Professor Adrian Williams. He’s been pioneering sleep research since the late 1970s. First at Harvard and UCLA and later here in the UK at St Thomas’ hospital and Kings College. I interviewed him for my podcast, which you can listen here. I’ve also collated all my research on sleep by topic below. Right at the end, I have the top tips to sleep well.

The Problem with a lack of sleep

  • Bad health. Less than six or seven hours a night demolishes your immune system, more than doubling your risk of cancer,  leads to high blood pressure, and raises risks of heart disease, stroke, Alzheimer’s and diabetes. 
  • Poor thinking. Lack of sleep also makes you feels sleepy (!) and impairs your thinking powers. In fact, after 16 hours of staying awake, your cognitive abilities are similar to being drunk at the legal driving limit. Vehicular accidents caused by drowsy driving exceed those caused by alcohol and drugs combined
  • Eat too much. Too little sleep swells concentrations of a hormone that makes you feel hungry while suppressing a companion hormone that otherwise signals food satisfaction. This leads to weight gain and societal lack of sleep may be a factor behind growing national obesity levels. Worse, should you attempt to diet but don’t get enough sleep while doing so, it is futile, since most of the weight you lose will come from lean body mass, not fat.

Benefits of sleep

  • Every major organ within the body, or process within the brain, is optimally enhanced by sleep
  • Dreaming provides a unique suite of benefits to all species : it mollifies painful memories and creates a virtual reality space in which the brain melds past and present knowledge, inspiring creativity.
  • Sleep restocks the armoury of our immune system, helping fight malignancy, preventing infection, and warding off all manner of sickness.
  • The physical and mental impairments caused by one night of bad sleep dwarf those caused by an equivalent absence of food or exercise.
  • Sleep is the single most effective thing we can do to reset our brain and body health each day—Mother Nature’s best effort yet at contra-death.

The Two Sleep Triggers

Two factors help sleep. The first factor, the circadian rhythm, is a signal beamed out from your internal twenty-four-hour clock located within your brain. The clock creates a cycling, day-night rhythm that makes you feel tired at night or alert during the day.

The second factor is a chemical substance, adenosine, that builds up in your brain and creates a “sleep pressure.” The longer you’ve been awake, the more that chemical sleep pressure accumulates, and consequentially, the sleepier you feel.

1)      Circadian rhythm

  • The circadian rhythm is the body’s own 24 hour clock. It controls other rhythmic pattern including  our timed preferences for eating and drinking, our moods and emotions, and the amount of urine we produce.
  • Natural peak of the human circadian rhythm in the early afternoon. Our average circadian clock runs around twenty-four hours and fifteen minutes in length. Sunlight corrects this imprecision to reset us to exactly 24 hours. So long as they are reliably repeating, the brain can also use other external cues, such as food, exercise, temperature fluctuations, and even regularly timed social interaction.
  • The  biological circadian rhythm coordinates a drop in core body temperature as we near typical bedtime  reaching its low point about two hours after sleep onset.

2)      Sleep Pressure

  • Right now, a chemical called adenosine is building up in tour brain. Adenosine is like a chemical barometer that continuously registers the amount of elapsed time since you woke up this morning.
  • Increasing adenosine in the brain is an increasing desire to sleep. This is known as sleep pressure.
  • As a result of that chemical sleep pressure, when adenosine concentrations peak, an irresistible urge for slumber will take hold. It happens to most people after twelve to sixteen hours of being awake.

Penalty against night owls

  • Night owls are people who struggle to wake up early and prefer to sleep late in contrast to  morning larks who wake early and sleep early. Despite cultural stories to the contrary, night owls are not owls by choice. They are stuck to a delayed schedule by unavoidable DNA hardwiring. It is not their conscious fault, but rather their genetic fate.
  • Not only do night owls have to deal with the stigma of being late risers,  society’s work/school scheduling favours morning larks.
  • This means, night owls are more chronically sleep-deprived, having to wake up with the larks, but not being able to fall asleep until far later in the evening.
  • The reasons for some people being night owls likely go back to our deep history. Humans likely evolved to co-sleep as families or even whole tribes, not alone or as couples. To maximise protection of the tribe, it would have made sense for people to have different waking patterns to ensure maximum vigilance.


  • The repeating signal of night and day is communicated to our brain and body using a circulating messenger called melatonin.  Melatonin is released at night.
  • But melatonin has little influence on the generation of sleep itself: a mistaken assumption that many people hold. Melatonin helps make you fall asleep, but doesn’t help you stay asleep.  Once sleep is under way, melatonin slowly decreases in concentration across the night and into the morning hours.

Jet Lag

  • For every day you are in a different time zone, our bodies can only readjust by about one hour. So if I fly from London to NY, it will take my body 4 to 5 days to fully adjust to the NY day.
  • Studies on people who travel a lot across time zones, such as pilots, have found that parts of their brains—specifically those related to learning and memory—had physically shrunk, suggesting the destruction of brain cells caused by the biological stress of time-zone travel. Also, their short-term memory was significantly impaired.
  • Taking melatonin helps overcome  jet lag. Take it around 4 hours before the preferred sleep onset time. Melatonin is not available over-the-counter in the UK, but is in the US. However, for over-the-counter products, the level of regulation is poor and so the melatonin content and quality varies widely. 

Sleeping Pills

  • Unlike melatonin, sleeping pills are benzodiazepines, which essentially are a variation of Valium. They sedate us, rather than generating real sleep. So taking them is not result in a refreshing sleep. 
  • Aside from melatonin, in the days before flying it is worth anticipating the target country’s time zone. So limit light exposure if the target country is at night and so on. 


  • Caffeine artificially mutes the sleep signal of adenosine and so makes you feel more alert and awake.
  • Caffeine peaks approximately 30 minutes after oral administration. The trouble is that it stays in your system after that – caffeine has an average half-life of 5-7 hours. Therefore it’s best not to have coffee after 2pm. 
  • Coffee and tea are not the only things that contain caffeine: dark chocolate, ice cream, and drugs such as weight-loss pills and pain relievers also contain caffeine.  Moreover, one cup of decaf usually contains 15 to 30% of the dose of a regular cup of coffee.
  • Some people have a more efficient version of the enzyme that degrades caffeine, allowing the liver to rapidly clear it from the bloodstream.
  • Aging also alters the speed of caffeine clearance: the older we are, the longer it takes our brain and body to remove caffeine, and thus the more sensitive we become in later life to caffeine’s sleep-disrupting influence. 
  • We also need to be aware of “caffeine crash.” This happens because even though caffeine is keeping you alert, the sleepiness chemical (adenosine) continues to build up, and so once the caffeine is processed in the liver, you get hit by the sleepiness build-up. 


  • Alcohol helps you fall asleep (it’s a sedative) , but as it gets processed by your body it disturbs your sleep and you end up with poor quality sleep (especially REM sleep).
  • Therefore it is best to stop drinking alcohol 3 hours before going to bed. 

Sign of sleep deprivation

  1. After waking up in the morning, could you fall back asleep at 10am or 11am?
  2. If you didn’t set an alarm clock, would you sleep past that time?
  3. Do you find yourself at your computer screen reading and then rereading (and perhaps rereading again) the same sentence?
  4. Can you function optimally without caffeine before noon?

If you answer “yes” to the first three and “no” to the last one, then you need more sleep.

What Happens In Sleep

  • We have two stages of sleep based: non–rapid eye movement (NREM) sleep, and rapid eye movement (REM) sleep.
  • We have 90-minute cycles of NREM and REM. In the first half of the night, the vast majority of our 90-minute  cycles are consumed by deep NREM sleep, and very little REM sleep, the last third of sleep the cycles are dominated by REM sleep. 
  • NREM or deep sleep is restorative and it repairs the body (including skin, one sign of poor sleep is dark rings around your eyes). It also weeds out and removes unnecessary neural connections and stores memories. 
  • REM sleep is when we dream. This stage rewires our brains and strengthens neural connections. Our body is also paralysed during this stage – otherwise we would act our dreams, which would be dangerous!
  • Given the above, if you wake too early, you miss crucial REM sleep (and brain repair) and if you go to bed too late, you miss crucial NREM sleep (and body repair).
  • A way of thinking about stages of sleep in terms of information processing is: the awake state is about reception (experiencing and  learning the world around you), NREM sleep is about reflection (storing and strengthening those new facts and skills), and REM sleep is about  integration (interconnecting these raw ingredients with each other, with all past experiences, and  building an ever more accurate model of how the world works, including innovative insights and problem-solving abilities). 

How much sleep?

  • Humans on average need 8 hours of sleep. The variation around the average is determined by your genes and family tree. So if you are from a family of (say) 6 hour sleepers, then the odds are that is your requirement too. One way to assess your sleep requirement is to go on holiday for two weeks, don’t set an alarm, and see how much you are sleeping in week 2.
  • Studies on hunter-gatherer tribes whose way of life has changed little over the past thousands of years, have observed the following:  these groups take a similarly longer sleep period at night (seven to eight hours of time in bed, achieving about seven hours of sleep), followed by a thirty- to sixty-minute nap in the afternoon.
  • The timing of sleep is linked to sunset and sunrise (for the equatorial tribes), which is connected to body cooling (you sleep when your body cools which would be after sunset).
  • Measurable in all human beings to date—is one consisting of a longer bout of continuous sleep at night, followed by a shorter mid-afternoon nap.

Siestas and sleep catch-up.

  • On study found that Mediterranean communities that abandoned regular siestas went on to suffer a 37 percent increased risk of death from heart disease across the six-year period, relative to those who maintained regular daytime naps.
  • However, cutting your overnight sleep to (say) 5 hours and then making up for sleep with a siesta could be detrimental as you would lose valuable REM sleep during your long sleep. So maintaining the long sleep is important. 
  • If you do have a siesta, it’s best time to wake up during REM state when are brains are more active. So it’s better to have short naps then long naps, which would make us enter NREM (and make us feel sluggish). 
  • More generally, catching up on sleep doesn’t work. We tend to be sleep deprived during the week and only sleep an extra 2 hours on the weekend, so the body doesn’t do the extra missed hours on weekends.
  • Equally, we cannot bank sleep. That is, sleep  lots one day to allow less sleep the following day. The sleep requirements work over 24 hour windows.

Wearable Tech

  • Most wearables don’t work. They measure movement vs non-movement which is not same as wake vs sleep.
  • The mainstream wearable that is probably best is the Fitbit 2, which derives the sleep state from our pulse rate.
  • The future is in non-wearables based on radar signals. The next few years should see more products coming to market.

 Ageing and Sleep

  • The amount of sleep required remains unchanged over our lives.  The fact that older people tend to sleep less is more due to less stable or consolidated sleep. This is due to things like interacting medications and diseases, but a lot to with a weakened bladder. Older adults therefore visit the bathroom more frequently at night, which could also expose them to light. Ironically, the ailments they are suffering from that destabilises their sleep, could be caused by the lack of sleep!
  • Another factor that affects older people’s sleep cycle is that they dose off on the couch numerous times during the day, which makes it harder for them to sleep for long time during the night. Another viscous spiral .
  • Youngsters, meanwhile, get their sleep affected most by exposure to blue light emitting from their gadgets late at night. 

Snoring and Sleep Apnea

  • Sleep disorders/apnea revolve around  interrupted breathing.  This comes either in the form of it stopping and restarting (central sleep apnea) or in the form of the throat closing off (obstructed sleep apnea).
  • Sleep apnea is marked by snoring. Snoring is caused by the throat narrowing and vibrating.  Half of middle-aged men snore and it is almost one of the most inheritable traits. The risk is when the throat closes off completely. One quarter of middle-aged men experience this. It often happens in the dream/REM sleep as muscles relax. It also occurs when you gain weight.
  • Snoring alone is not enough to diagnose you with sleep apnea, but if it is accompanied by sleepiness during the day and poor quality sleep during the night (you keep waking up gasping for breath), then see a doctor.

Importance of Temperature

  • Modernity has messed  up the connection between environmental light and temperature. Ideally, when it gets and dark and cold, your body sleeps more easily. Today, with indoor heating and artificial light, our bodies get fooled into thinking its day-time. 
  • To cool the body, our hands, feet, and head are remarkably efficient radiating devices that, just prior to sleep onset, jettison body heat in a massive thermal venting session so as to drop your core body temperature.
  • Also, humans have developed the pre-bed ritual of splashing water on one of the most vascular parts of our bodies—our face, using one of the other highly vascular surfaces—our hands. You may think the feeling of being facially clean helps you sleep better, but facial cleanliness makes no difference to your slumber.
  • This is also the reason that you may occasionally stick your hands and feet out from underneath the bedcovers at night due to your core becoming too hot, usually without your knowing.
  • A bedroom temperature of around 65 degrees Fahrenheit (18.3°C) is ideal for the sleep of most people, assuming standard bedding and clothing.

 Tips To Sleep Well

  • Exercise – raise your body temperature and pulse rate for 20 minutes in the early evening
  • Get up at a regular time to get exposed to light. This is much more important than going to bed at a regular time – in fact, you should go to bed when you are sleepy, otherwise you could start to get sleep anxiety.
  • Sleep in a cool, dark, quiet bedroom (like a cave, bats sleep well!)
  • Minimise  late exposure to electronic light, especially blue light (you can change your phone/laptop settings to remove blue lights in the evening, you can also buy glasses to remove blue lights when watching TV)
  • Don’t consume caffeine after 2pm.
  • Don’t drink alcohol 3 hours before bed. Similarly avoid nicotine.


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2 thoughts on “Sleep: Everything You Wanted To Know, But Were Too Tired To Ask”

  1. Very informative article but the question remains if you work in a high pressure environment such as Corporate Finance where you are expected to churn out 15+ hour days how can we expect firms to acknowledge the importance of sleep?

    1. That’s a good question. Hopefully if firms understand the science of sleep they will realise that not only will they have underperforming employees but also they will reduce the risk to the firm. For example, sleep deprivation has similar effects on you as being drunk and firms don’t allow employees to drink on the job, so….

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