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

One of the principal functions of rapid eye movement sleep that we now have understood is that it seems to provide a form of overnight therapy. REM sleep is emotional first aid. It's during REM sleep that we take the emotional concerns—and even sometimes, in extreme examples, some of the traumatic events that we've been experiencing—and REM sleep almost acts like a nocturnal soothing balm. It tries to take the sharp edges off those difficult experiences so that when you come back the next day, you don't necessarily feel as emotional as you did about those events the day before ... It's not time that heals all wounds; it's time during REM sleep and dreaming that provides this emotional convalescence.

The ratio of non-REM to REM [sleep] within each 90-minute cycle as we move across the night changes ... In the first half of the night, the majority of those 90-minute cycles are going to be comprised of lots of deep, non-rem sleep (stages three and four non-REM sleep) and very little REM sleep, but as you push through to the second half of the night, now the brain has a shift in its taste preference for what it wants to feast on at the finger buffet of sleep stages. Instead, now it actually wants to consume much more REM sleep and it's lost its appetite for deep non-REM sleep. So, in the second half of the night, the majority of those 90-minute cycles are comprised much more of REM sleep.

The downside of naps is that they can take away just what you described, which is sleep pressure ... If you are struggling with sleep at night, avoid naps during the day ... If you are already having problems either falling asleep, which is what we call sleep-onset insomnia, or you can fall asleep but you can't stay asleep, which is what we call sleep maintenance insomnia, you want to build up as much sleep pressure [and] as much sleepiness as you possibly can during the day.

Dr. Matthew Walker explains the stages of sleep.

Individuals who report getting less than seven hours of sleep a night are almost three times more likely to become infected by the rhinovirus, which is the common cold, relative to those who sleep more than seven hours.

If you're not getting sufficient sleep in the week before you get your flu shot, you end up producing less than 50% of the normal antibody response, therefore rendering that flu vaccination significantly less effective.

Part of my take on COVID-19 vaccines is going to be: I think it's going to take a little longer than we think; I think it's going to probably not be quite as safe as we think, meaning not something you just want to indiscriminately give to everybody—in other words, like any vaccine, I think it's going to have some risk; and it's certainly possible that at least some of those vaccines, potentially really efficacious ones, may come with side effects that are undesirable, and therefore, we'll have to think about who gets them.

There was a fascinating study where they were selectively depriving mice of sleep, particularly REM sleep, and what they found is that when they were exposed to malaria, the mice that were deprived of sleep were far more likely to die as a consequence of that malaria exposure than the well-rested mice.

If you are struggling with sleep, remove all clock faces from your bedroom. It's not going to help you to know that it's now 2:35 AM and you've still not been able to fall asleep. It's only going to trigger more anxiety.

Women who were sleeping five hours or less were 70% more likely to go on to develop pneumonia.

Adenosine build-up drives the need for deep sleep.