Picture this: it’s bedtime. The curtains are drawn tight and your blue-light-emitting technological devices have been retired to your nightstand drawer. You’ve quit drinking after-dinner espressos (so far so good) and swapped out your bourbon nightcap for an actual nightcap and pair of flannel pyjamas.
Hold it right there. That last one might not be such a good idea.
But just to make sure you’re doing everything else right, let’s run down the checklist of essential sleep hygiene first:
No excessive daytime napping (naps lasting more than two hours)
Avoid irregular bedtimes/waking times
Avoid intense exercise (enough to break a sweat) an hour before bedtime
Don’t stay in bed after waking up (apart from the occasional weekend lie-in)
No alcohol, tobacco, or caffeine within four hours of going to bed (or in bed!)
Avoid going to bed stressed, angry, upset, or nervous
Don’t ruminate, plan, or worry in bed
Don’t use your bed for activities other than sex and sleep (even reading is out, unfortunately)
Avoid uncomfortable bedding (poor quality mattress/pillows, bedding with too much or too little insulation)
Don’t schedule important tasks right before bedtime (bill paying, studying, etc.)
Make sure your bedroom is as dark as possible, quiet (less than 35 decibels, slightly quieter than a library), and well-ventilated
And, back to the flannel PJs:
Ensure you’re not too hot or too cold
Temperature regulation and sleep
The optimal ambient temperature for sleep is anywhere between 17 and 28 degrees Celsius (63 to 82 degrees Fahrenheit) depending on airflow and humidity, the amount of insulation provided by bedding and/or clothing, and body temperature.
Optimal temperature differs by sex. When clothed and in a room with a comfortable 50% relative humidity, men self-reported better sleep quality at 17 degrees Celsius (63 degrees Fahrenheit) while women preferred 23 degrees Celsius (73 degrees Fahrenheit).
At night, our core body temperature declines due to the release of melatonin, a drop in metabolic rate, and cessation of physical activity. Thermosensitive cells in the preoptic and anterior hypothalamic regions of the brain receive this signal and facilitate sleep onset. Simply put, this means that when you cool down, your body knows it’s time to rest.
Sleep is difficult to initiate and maintain unless body temperature is kept within the thermoneutral zone. This is the temperature at which heat production and heat dissipation from the skin surface are in perfect balance, requiring neither heat production by shivering, nor the cooling effects of sweat.
Research shows that being too cold or too hot increases the frequency of waking in the night, leading to poor-quality sleep. Furthermore, overheating alters sleep architecture (the length and latency of the various sleep phases). In other words, sleep is organized into various phases characterized by different brain wave patterns and levels of muscle tone. Irregular cycling through, or skipping, these phases leads to adverse physiological consequences.
Likely as a means of conserving energy, overheating results in prolonged stage four sleep, a deep sleep characterized by slow, delta brainwaves. As a consequence, the amount of REM sleep — which is vital to emotional regulation, by the way — decreases.
The case for sleeping in the nude
Sleepwear may cause overheating and sweat production and, in turn, discomfort when moisture clings to clothing.
Unlike overheating, cold exposure will not affect the length and latency of the various sleep phases, so sleeping in the nude is less risky than getting overly toasty in your flannels. While a blanket is easily shirked off in the night, this is not the case with clothing, which can easily lead to potentially disrupted sleep.
Sleeping in the nude has been found to have an invigorating effect on one’s sex life—at least according to a study funded by a mattress company. (The highest level of scientific evidence possible.)
Finally, ambient temperature interacts with skin and core temperature, humidity, airflow, and the amount of insulation provided by bedding/clothing. Sleeping in the nude simplifies this equation and improves your chance of restful sleep.
Perhaps the only downside to sleeping nude is that you can’t facilitate a 5 a.m. workout by going to bed in your gym gear. But the trade-off is certainly worth it, as thermal regulation boosts both sleep onset and quality.
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