1: Many people swear by a bath before bedtime.  We believe we fall asleep faster because we feel “toasty and warm to the core,” writes Matthew Walker in Why We Sleep: Unlocking the Power of Sleep and Dreams.

“Hot baths prior to bed can induce 10 to 15 percent more deep NREM (deep) sleep in healthy adults,” he notes.  

But not for the reason we think.  

A “hot bath invites blood to the surface of [our] skin, giving [us] that flushed appearance,” writes Matthew.  When we get out of the bath, “those dilated blood vessels on the surface quickly help radiate out inner heat, and [our] core body temperature plummets.  Consequently, [we] fall asleep more quickly because [our] core is colder.”  

To fall asleep faster and experience better quality sleep, we need to lower our core temperature by 2 to 3 degrees Fahrenheit, he explains.  One way to control our body temperature is by paying attention to the surface of our skin in three specific body parts: our hands, our feet, and our head.  

“All three areas are rich in crisscrossing blood vessels that lie close to the skin’s surface,” notes Matthew. “The hands, feet, and head are therefore remarkably efficient radiating devices that, just prior to sleep onset, jettison body heat in a massive thermal venting session so as to drop [our] core body temperature.  Warm hands and feet help [our] body’s core cool, inviting sleep quickly and efficiently.”

Which is why we may occasionally stick our hands and feet out from underneath our blankets, usually without realizing what we’ve done or why.  

Should we have children, Matthew writes, we’ve “probably seen the same phenomenon when [we] check in on them late at night: arms and legs dangling out of the bed in amusing (and endearing) ways, so different from the neatly positioned limbs [we] placed beneath the sheets upon first tucking them into bed.  The limb rebellion aids in keeping the body core cool, allowing it to fall and stay asleep.”

2: For optimal sleep, Matthew recommends a bedroom temperature of around 65 degrees Fahrenheit.  “This surprises many, as it sounds just a little too cold for comfort,” he writes.  “Most of us set ambient house and/or bedroom temperatures higher than are optimal for good sleep and this likely contributes to lower quantity and/or quality of sleep than you are otherwise capable of getting.  Lower than 55 degrees Fahrenheit can be harmful rather than helpful to sleep, unless warm bedding or nightclothes are used.  However, most of us fall into the opposite category of setting a controlled bedroom temperature that is too high: 70 or 72 degrees.”

He contrasts our sleep practices with pre-industrial cultures of hunter-gatherers who “sleep in porous huts with no cooling or heating systems, minimal bedding, and lie semi-naked.  They sleep this way from birth to death.  Such willing exposure to ambient temperature fluctuations is a major factor (alongside the lack of artificial evening light) determining their well-timed, healthy sleep quality.”

Paying attention to the room temperature is a crucial driver of sleep quality and shedding heavy bedding and excess nighttime attire.  When treating insomnia, sleep clinicians will often recommend patients drop their current thermostat set-point by 3 to 5 degrees Fahrenheit from what they currently use.

In one experiment, researchers used a whole-body thermal sleeping suit to control and lower the skin’s temperature.  The results?  “Sleep took hold of the participants in a significantly shorter time,” Matthew writes, “allowing them to fall asleep about 20 percent faster than was usual. The improvement in the insomniacs was even more impressive—a 25 percent reduction in the time it took to drift off into sleep.”

But that’s not all.  “Before the body-cooling therapy, these groups had a 58 percent probability of waking up in the last half of the night and struggled to get back to sleep—a classic hallmark of sleep maintenance insomnia,” he notes.  “This number tumbled to just a 4 percent likelihood when receiving thermal help from the bodysuit.”

3: One additional recommendation from Matthew: Turn off the snooze button.  If we use an alarm clock, he suggests getting in the habit of waking up only once to spare our hearts “the repeated shock. . . [of a] cardiovascular spike again and again within a short span of time.”

More tomorrow!


Reflection: What temperature do I set on the thermostat before going to bed?

Action: Experiment with 65-68 degrees Fahrenheit to see how this temperature impacts my sleep quality.

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