August 31, 2020


#126 – Matthew Walker, Ph.D.: Sleep and immune function, chronotypes, hygiene tips, and addressing questions about his book

“It's not time that heals all wounds. It's actually time during REM sleep and dreaming that provides this emotional convalescence.” — Matthew Walker, Ph.D.

Read Time 21 minutes

In this episode, sleep expert Matthew Walker returns by popular demand to dive deeper into many sleep-related topics, starting with what we’ve learned about sleep through the lens of the COVID-19 pandemic and how sleep impacts the immune system. He then covers topics such as how dreaming affects emotional health, the different sleep chronotypes, the best sleep hygiene tips, and the pros and cons of napping. Matthew finishes by addressing several of the errors that readers have pointed out in his book, Why We Sleep.


We discuss:

  • Three ways that the coronavirus pandemic has impacted sleep [3:30];
  • The importance of dreaming for emotional health, and how the coronavirus pandemic has increased dreaming [11:45];
  • The impact of alcohol consumption on sleep quality and stress levels [20:00];
  • Sleep’s impact on the immune system, and implications for a future COVID-19 vaccine [27:45];
  • What determines how much deep sleep and REM sleep you need? [36:30];
  • Pros and cons of napping, and insights from the sleep habits of hunter-gatherer tribes [42:15];
  • Sleep hygiene, wind-down routine, and tips for better sleep [56:45];
  • Understanding sleep chronotypes and how knowing yours could help you [1:06:00];
  • Night terrors in kids—what they are and why they happen [1:16:30];
  • Addressing errors found in Matt’s book, Why We Sleep [1:20:45]; and
  • More.


Three ways that the coronavirus pandemic has impacted sleep [3:30]

The COVID-19 pandemic has impacted sleep in 3 ways:

  1. The amount that people are sleeping
  2. The timing of the sleep
  3. Dreaming

1—Amount of sleep:

A sleep tracking company that released data on ~68,000 individuals

  • They found total sleep time had increased across the entire country by ~20% 

Two peer-reviewed papers from Current Biology added more nuance—

  1-Total amount of sleep had increased by 15 minutes

  2-Social “jet lag” had decreased

  • Meaning, the difference between the sleep that you’re getting during the week versus the weekend
  • Many people are sleeping less due to obligations during the week (getting kids to school, being at work on time, getting home late after a long commute, etc.) 
  • And then they sleep more on the weekends to “make up” for the lost sleep
  • Since COVID-19 began, people are sleeping more during the week without those same week-day obligations and their “sleep opportunity” has increased

  3-Subjective sleep quality had decreased in a subset of people

What Matt thinks is probably happening across the country:

  • There’s going to be at least two different clouds of data 
    • i) people for whom sleep time AND quality both increased, and 
    • ii) people for whom sleep became shorter and worse
      • Why? ⇒ They’ve either lost their job, may lose their job, or just in general they have a great deal of anxiety because of COVID. 

2—Timing of sleep:

  • This study showed people were going to bed about 30 minutes later and waking up about 50 minutes later the next morning
  • Matt says “night owls are being allowed to be much more owl-like and sleeping in harmony with their chronotype.

3—Dreaming: People have been reporting having more dreams since the pandemic began 

(more on this in the following section)


The importance of dreaming for emotional health, and how the coronavirus pandemic has increased dreaming [11:45]

How has dreaming been impacted by the coronavirus pandemic? 

  • Dreaming has increased
  • Two different reasons—

{end of show notes preview} 

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Matthew Walker, Ph.D.

Dr. Walker earned his degree in neuroscience from Nottingham University, UK, and his PhD in neurophysiology from the Medical Research Council, London, UK. He subsequently became a Professor of Psychiatry at Harvard Medical School, USA. Currently, he is Professor of Neuroscience and Psychology at the University of California, Berkeley, USA. He is also the founder and director of the Center for Human Sleep Science.

Dr. Walker’s research examines the impact of sleep on human health and disease. He has received numerous funding awards from the National Science Foundation and the National Institutes of Health, and is a Kavli Fellow of the National Academy of Sciences.

Dr. Walker is the author of the International Bestseller, Why We Sleep. It has a singular goal: to reunite humanity with sleep.

In addition, Dr. Walker is an internationally recognized speaker, a successful entrepreneur, and a Sleep Scientist for Google.



Center for Human Sleep Science

Matthew’s publications

Disclaimer: This blog is for general informational purposes only and does not constitute the practice of medicine, nursing or other professional health care services, including the giving of medical advice, and no doctor/patient relationship is formed. The use of information on this blog or materials linked from this blog is at the user's own risk. The content of this blog is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Users should not disregard, or delay in obtaining, medical advice for any medical condition they may have, and should seek the assistance of their health care professionals for any such conditions.


  1. Thank you sooo much for this broadcast
    It is full of great information and very beneficial

  2. Thank you. That was a very informative and interesting conversation.
    The part about getting good sleep prior to getting an immunization was timely because I am weighing when to get a flu shot.

    With respect to a Covid-19 vaccination, it seems that there are some reactions like pain being reported in the testing groups. But that reminded me that taking pain relievers might counter the immune response. I wondered what your thoughts might be on this topic.

    I know you will be talking more about different Covid-19 vaccines in the future.
    I’ll stay tuned.


    Effect of antipyretic analgesics on immune responses to vaccination

    Immunologic effects of yogurt

  3. Might you post the link to the chronotypes quiz that was mentioned? I’m 97% sure I’m an extreme night owl based on my natural inclination to stay up until 1 and wake at 9. I’ve felt so dejected and “lazy” being on a different schedule with work and boyfriends/family. The best thing about being laid off is being able to be true to my biology and feeling more invigorated and creative. If only more businesses and such would recognize we are out here and NOT providing any quality work before 9 or 10 am. 😉

  4. Listening again to Matthew Walker reassuringly re-present the evidence for medicinal sleep helps again to assuage my hypercortisolemia ! But to assuage his own, over the issue of confessed errors in his last book, I should think a little self-forgiveness is in order. For example : “over half a million individuals” versus “474,684” OR equating an agency of the WHO with the WHO itself hardly makes him guilty of obscurantism ! Yet given the Pravda-like Culture of Pan-Mendacity peddled from the WH these days (where mistakes are never conceded), I also find Dr. Walker’s self-critical conscience to be refreshing.

    As for the mental malady of “perfectionism” (of which too many of us suffer) that perhaps could be a podcast or two in its own right ; whose partial remedy might be found in the transcultural Art of Imperfection (as in ancient Hebrew poetry or the “spirit line” on the border of Navajo rugs or the concept of ‘Wabi sabi” in Japanese pottery or even in Gödel’s humbling incompleteness theorem ! )

  5. I was disappointed (to put it mildly) by Dr. Walker’s characterization of the kinds of errors that had been found in the book:

    He presented the most minor of the errors as if they were representative, and also mischaracterized some of the critiques that had been raised.

    For instance, he acted as if his interpretation of the data showing that long-sleepers *also* have increased mortality (namely, that it was the result of confounding with or reverse-causation with pre-existing or subclinical disease) merely needed updating to include more subtle nuances, and completely side-stepped the core of the critique, which is that the association of *short* sleep with early mortality may also be due to confounding or reverse causation: for instance, having a stroke can lead to insomnia:

    … so a person with undiagnosed stroke or TIA may be getting less sleep because of existing cardiovascular disease, and not the other way around. The same is true for many other known causes of secondary insomnia, including asthma, depression, cancer, some medications, or current or recovering-relapsing alcohol abuse.

    He retreats from “short sleep doubles your risk of cancer” to “short sleep doubles your risk of *some* cancers,” ignoring the fact that one of his citations is a meta-analysis that “showed no significant relationship between sleep duration and [overall] cancer risk”, except for a possible effect in Asians:

    So does Dr. Walker believe that short sleep duration halves the risk of some cancers, but increases the risk of some others so that it all balances out?

    There’s also the rather damning charge of data manipulation, which seems pretty hard to rebut innocently and was not addressed:

    Putting this all together makes his anguished confession of trivial errors seem disingenuous.

  6. Peter, I would love if you and Matthew could discuss sleep and the moon, and specifically sleep and women’s menstrual cycles.

    I notice the affects of the moon on my cycle, and my sleep. Is this anecdotal or biological for most women?

  7. Hi Peter, would love if you and Matthew in your next podcast could go into more detail around what the ideal sleep cycle is: Monophasic, Biphasic, Polyphasic.

    In all his works (written and podcasts) he seems to elude to the Biphasic schedule as the biologically instinctive way we would all sleep if society didn’t enforce monophasic on us, but never goes into much detail about it other than to say it is what hunter gatherers appeared to do, and in the case of those who adopt it they have some health benefits.

    If the answers are not known, it also may be a good place for some additional research into working our what is best, and under what conditions each of the alternatives might be good to implement in a specific use case. (eg as parent with a newborn it might be best to temporarily adopt a polyphasic schedule for the first few months of the child’s life until they adapt to a biphasic or monophasic schedule)

    And if Biphasic is the ideal, what durations would be better? Do they differ in benefit at all? 7.5H + 0.5H or 7H + 1H or 6.5H + 1.5H

    Is the post lunch nap better to be taken later or earlier, would this change if you are a Lark or an Owl?

    Would be great to get some more detail on all these questions

  8. What Matthew says in this podcast about fast metabolizers of alcohol contradicts what he said in his book (Why We Sleep).

    From the podcast notes:
    > Matthew confirms this observation — if you do some of the genetic testing you can see that some people are fast metabolizers of alcohol (same with caffeine)
    > And in those fast-metabolizers, by the time their brain is ready for REM sleep, the metabolic consequences of alcohol degradation—the aldehydes and ketones—are no longer present

    From his book, pg 179:
    > Glib advice aside, what is the recommendation when it comes to sleep and alcohol? It is hard not to sound puritanical, but the evidence is so strong regarding alcohol’s harmful effects on sleep that to do otherwise would be doing you, and the science, a disservice.

    > Many people enjoy a glass of wine with dinner. ***But it takes your liver and kidneys many hours to degrade and excrete that alcohol, even if you are an individual with fast-acting enzymes for ethanol decomposition. Nightly alcohol will likely disrupt your sleep, and the annoying advice of abstinence is the best, and most honest, I can offer.***

    I’m curious if he changed his mind on the impact of alcohol on fast metabolizers, and if there were particular studies that influenced this.

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