This book looks at all the latest research on the importance of sleep, a lot of which has been conducted by the author himself. It’s a horrifying read for anyone who frequently fails to achieve the desired 7.5 to 8 hours sleep required by the brain (and body) each night and urges you to make sleep a priority.
The topic of sleep was covered already in Sleep Smarter but the focus here includes more of the science of sleep. The author delves into REM and Non-REM (Rapid Eye Movement) sleep and the various benefits each contributes to your short and long term memory, decision-making, learning and emotion. He busts the myth of being able to “catch up” on sleep at the weekend and also covers practical tips for improving sleep quality and duration. Unless you are already a sleep expert then I believe you will find this book very valuable. I can all but guarantee it will make you re-assess how important sleep is in the grand scheme of things. I believe it will be particularly beneficial for anyone who has trouble sleeping, regularly uses sleeping pills, is involved in late/early shift work or averages 6 or fewer hours of sleep on a regular basis.
Why We Sleep by Matthew Walker
PRO TIP: Take notes! When you read a book, use a blank sheet of paper as a bookmark. Write down any interesting facts and information from the book. This condenses a whole book into 3-4 pages of key notes that are important and relevant to you.
My Notes
- Routinely getting less than 6 or 7 hours sleep more than doubles cancer risk
- One night of poor sleep disrupts blood sugar enough to make you appear pre-diabetic if seen by a doctor
- Car accidents from drowsy driving exceed that of drink driving
- Our circadian rhythm is not exactly 24 hours and an experimenter found it to be between 24 and 26 hours
- Morning people (40% of population), Evening people (30% of pop.) and those in-between (30%) have been established as having different genetic chronotypes
- If you are a “night owl” (evening person) you will be disrupted by a standard 8am-5pm job, often feel sleep deprived and struggle with productivity before 10am. This leads to higher rates of depression, anxiety, diabetes, cancer, heart attack and stroke.
- Once asleep, melatonin decreases across the night. As sunlight enters the brain through the eyes (even if closed!), melatonin is shut off.
- Caffeine’s half-life is 5-7 hours, meaning you still experience half the effect after that time and 1/4 of it after ~12 hours
- A greater % of REM sleep occurs in later cycles, so while 6 hours instead of 8 hours is 75%, you may only get 50-60% of your REM sleep in that time.
- Reduced sleep during fasting occurs as your brain thinks food is scarce and makes being awake to find food a priority.
- Bi-phasic sleep (30 to 45 minute afternoon nap) is associated with reduced death.
- A study showed only 2 glasses of wine significantly impaired REM sleep in the unborn child.
- Drinking while breastfeeding also impairs REM sleep by 20-30%.
- Younger children have a circadian rhythm that requires an earlier bed time than an adult while teenagers are slightly later than adults so genuinely require a lie-in (they aren’t just lazy!)
- You lose about 70% of your deep sleep by age 70.
6 hours sleep vs. 8 leads to:
- 10-30% reduction in time to exhaustion during exercise
- Reduction in aerobic output
- Decrease in vertical jump height (measure of explosive power)
- Decrease in strength
- 60% higher emotional reaction to a stimulus
Increased frequency of injury among athletes based on sleep (see table below)
Average hours slept per work night in different countries (see table below)
- Performance was 400% worse on a reaction test after being awake for 24 hours, or from 6 hours sleep on 10 consecutive nights vs. full 8 hours.
- Being awake for 19 hours is comparable to being too drunk to drive in terms of decision-making and reaction times
- There is a rare gene some possess whereby you can survive on less than 6 hours sleep per night, but fewer than 1 in 12,000 people have it
- Adults over 45 with less than 6 hours sleep were 200% more likely to have a heart attack/stroke than those who got 7-8 hours
- Sleep deprivation decreased leptin (satiety hormone) and increased ghrelin (hunger hormone), the more sleep deprived individuals also had higher cravings for junk food.
- Sleep is so vital the W.H.O. classed night time shift work as a “probable carcinogen”.
- Two forms of insomnia are sleep onset (trouble getting to sleep) and sleep maintenance (trouble staying asleep).
- Improve sleep by using mood lighting in the evening, using blackout curtains and a blue-light blocking app on electronic devices e.g. f.lux
- Alcohol increases sleep disruption and suppresses REM sleep.
- The single most effective way to improve sleep is to have a set bed time and wake time, even at weekends.
- Allow time to relax and unwind before bed (30-60 minutes with no electronics).
- Get at least 30 minutes of sun exposure in the day to improve signals for your body to sleep at night.
