Why We Sleep

Chapter 13: What Stops You From Getting Good Sleep

Five influences have drastically changed how we sleep: caffeine, light, temperature, alcohol, and alarms.

Caffeine

This was already discussed in chapter 2. The tips, for good measure:

  • Caffeine is of course in coffee, some soft drinks, and some teas, but also chocolate.
  • Be careful when drinking decaf, as it apparently contains 15-30% of the caffeine in regular coffee - it’s nowhere near zero caffeine.
  • If you must have it, don’t drink it in the afternoon, and definitely not in the hours before sleep.

Light

Light is a signal for the suprachiasmatic nucleus to regulate the circadian rhythm (by signaling to the pineal gland to secrete melatonin). In the natural world, when the sun goes down, there’s little light. But nowadays, artificial light bathes our homes and disrupts our circadian rhythm.

Any light is disruptive to the circadian rhythm. Electric light delays your 24-hour circadian rhythm by 2-3 hours each evening.

  • Even 8-10 lux (a measure of light intensity) delays melatonin release. A bedside lamp is 20-80 lux, and a typical living room is 200 lux, suppressing melatonin by 50%. (In comparison, the full moon only provides about 0.1 lux.)
  • Light can suppress melatonin for days after usage stops.

Blue light is most problematic, suppressing melatonin at twice the levels of warm light. Blue light is most strongly emitted by digital screens like TVs, computer monitors, and smartphones.

  • We respond most to blue light because we evolved from marine creatures, and blue light penetrates water best.
  • Reading on an iPad vs a book causes 50% less melatonin secretion and delayed the rise by 3 hours.

Tips:

  • Dim lights in the rooms where you spend evenings.
  • Maintain complete darkness throughout the night, using blackout curtains.
  • Use settings on your phone and computers to tint the screen orange, reducing blue light.
  • Consider yellow-tinted glasses that block blue light.

Constant temperature

In natural environments, the temperature rises and falls with the day. This is used by the hypothalamus, along with light, to set the circadian rhythm. Our bodies react in kind -- before sleep, the body cools, ejecting heat through densely perfused areas like hands, feet, and face.

But in modern days, we use thermostats to homogenize our temperatures, suppressing the highs in the day and raising the lows with pajamas and blankets. Our brain doesn’t get the same signal about the day’s cycle that it used to.

Cooling body temperatures improves sleep. In an experimental treatment, people wear a bodysuit that circulates cool water. Among insomniacs and the elderly, this reduces time to sleep and increases the quality of NREM sleep.

Tips:

  • The best temperature to sleep at with standard bedding and clothing is 65F, which is far lower than most people keep bedrooms.
  • Try activities that help remove heat from the body:
    • Hot bath before bed (expands capillaries, which after bath drops temperature)
    • Splashing water on your skin
    • Sticking your hands and feet outside the blanket

Alcohol

Alcohol is a sedative, causing what appears to be sleep but is really more like anesthesia. It disrupts sleep by suppressing REM sleep and causing waking throughout the night. This is caused by aldehydes from alcohol metabolism.

Alcoholics are so sleep-deprived that their brain imposes REM-like behavior during wakefulness, such as hallucinations and scattered thinking. (Shortform note: an unfortunate vicious cycle can result here -- alcohol disrupts sleep, which causes more fatigue and less behavior control when awake, which prompts more alcohol.)

By disrupting REM sleep, alcohol disrupts the normal processes of learning and complex knowledge.

  • In an experiment, subjects were tasked with learning a new grammar on day 1. When exposed to alcohol on the first night, they lost 50% of memory recall compared to the abstinent group. Surprisingly, those getting alcohol on night 3 lost 40% - damage can occur for memories days past.

Tips:

  • The author encourages total abstinence from alcohol, as puritanical as that sounds. A drink takes hours to fully degrade and excrete, and it’s even worse for people with alcohol flush reactions.

Alarms

Alarms cause acute stress responses when you wake up, spiking cortisol, heart rate, and blood pressure. This is not good for you. Even worse, snoozing the alarm causes multiple stress responses in quick succession.

The best path to waking is natural, without alarms. Wake up at the same time of day every day. If you have to, commit to waking up when you hear the alarm, to avoid snoozing.

“Life hacks” on how to defeat the snooze button are missing the point - rearrange your sleep so you wake up naturally.