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← How caffeine and alcohol affect your sleep

Caffeine wakes you up, and alcohol makes you nod off, right? It's not that simple. Sleep scientist Matt Walker takes us into the eye-opening ways that these drinks affect the quantity and quality of our sleep.


Showing Revision 6 created 09/02/2020 by Erin Gregory.

  1. Many of us like to start the day
    with a cup of coffee
  2. and perhaps end the day
    with a glass of wine
  3. or some other kind of alcoholic drink.
  4. But it turns out
    that these two substances,
  5. alcohol and caffeine,
    can have surprising impacts on our sleep.
  6. [Sleeping with Science]

  7. (Music)

  8. Let's start with caffeine.

  9. Caffeine is in a class of drugs
  10. that we call the psychoactive stimulants.
  11. And everyone knows that caffeine
    can make them more alert.
  12. It can wake them up.
  13. But there are at least two additional,
  14. hidden features of caffeine
  15. that some people may not be aware of.
  16. The first is the duration
    of action of caffeine.

  17. Caffeine, for the average adult,
  18. will have what we call a half-life
  19. of about five to six hours.
  20. What that means is that
    after about five to six hours
  21. 50 percent of that caffeine that you had
  22. is still circulating in your system.
  23. What that also means
    is that caffeine has a quarter-life
  24. of about 10 to 12 hours.
  25. In other words, let's say
    that you have a cup of coffee
  26. at 2pm in the evening.
  27. It could be that almost
    a quarter of that caffeine
  28. is still swilling around
    in your brain at midnight.
  29. And as a result, it can make
    it harder for an individual
  30. to fall asleep or even stay asleep soundly
  31. throughout the night.
  32. So that's the first feature of caffeine.
  33. The second issue with caffeine

  34. is that it can change
    the quality of your sleep.
  35. Now some people will tell me
  36. that I'm one of those individuals
  37. who can have an espresso with dinner,
  38. and I fall asleep fine,
    and I can stay asleep.
  39. But even if that's true, it turns out
  40. that caffeine can actually
    decrease the amount
  41. of deep, non-rapid eye movement
    sleep that we have,
  42. stages three and four of non-REM sleep.
  43. That's that sort of
    restorative deep sleep.
  44. And as a consequence,
    you can wake up the next morning,
  45. and you don't feel refreshed,
  46. you don't feel restored by your sleep.
  47. But you don't remember waking up,
  48. you don't remember
    struggling to fall asleep,
  49. so you don't make the connection,
  50. but nevertheless
    you may then find yourself
  51. reaching for two cups of coffee
    in the morning to wake up
  52. rather than one.
  53. So that's caffeine,
    but now let's move on to alcohol,

  54. because alcohol is perhaps one
  55. of the most misunderstood
    sleep aids out there.
  56. In fact, it's anything but a sleep aid.
  57. And it can be problematic for your sleep
  58. in at least three different ways.
  59. First, alcohol is in a class of drugs

  60. that we call the sedatives.
  61. But sedation is not sleep.
  62. And studies teach us that those two things
  63. are really quite different.
  64. Sedation is a case
  65. where we're simply
    switching off the firing
  66. of the brain cells,
    particularly in the cortex.
  67. And that's not natural sleep.
  68. In fact, during deep
    non-rapid eye movement sleep,
  69. for example, the brain has
    this remarkable coordination
  70. of hundreds of thousands of cells
  71. that all of a sudden fire together,
  72. and then they all go silent,
  73. and then they all fire together,
    and then they go silent,
  74. producing these big, powerful brainwaves
  75. of deep non-REM sleep.
  76. And so that's the first way
  77. in which alcohol can be problematic.
  78. We're mistaking sedation for deep sleep.
  79. The second problem with alcohol

  80. is that it can actually
    fragment your sleep.
  81. Alcohol can actually trigger
    and activate during sleep
  82. what we call the fight or flight branch
  83. of the nervous system,
  84. which will therefore
    wake you up more frequently
  85. throughout the night.
  86. And alcohol can even increase the amount
  87. of alerting chemicals
    that are released by the brain,
  88. once again fragmenting your sleep.
  89. The third and final issue
    with alcohol and sleep

  90. is that alcohol can actually block
  91. your rapid eye movement sleep,
    or your dream sleep.
  92. And as we'll learn in subsequent episodes,
  93. REM sleep, or rapid eye
    movement sleep, dream sleep,
  94. provides a collection of benefits,
  95. things such as your emotional
  96. and mental health, even creativity.
  97. Now I'm not here
    to tell anyone how to live.

  98. I don't want to be puritanical.
  99. I'm just a scientist.
  100. What I want to try and do is provide you
  101. with the information
    about the relationship
  102. between caffeine and alcohol on your sleep
  103. so then you can make an informed choice
  104. as to how best you want to live your life
  105. when you're trying to
    prioritize your sleep health.