Polyphasic Sleep

Thermoregulation and Sleep

By Nade

Thermoregulation is an integral part of sleep homeostasis. Throughout the day there are dips in core body temperature in preparation for sleep. When we are first adapting to polyphasic sleep we have a thermoregulation habit based on monophasic sleep, which means we will be cold at night and warm in the day, because we are expected to be asleep at night and awake in the day.

In order to change your thermoregulation to better fit polyphasic sleep, you must give your body the right stimulus. The response to external cold is for the body to warm its self up, and the response to external heat is for the body to cool itself down. Many people not understanding this basic response system will try to keep themselves warm with artificial external heat (blankets, heating, and clothes). The result is that their body remains in a warm adapted state, in preparation for the warm external stimulus, and they keep cold-core body temperature at night (and with the comes sleepiness). 

Armed with the knowledge that external heating is keeping you cold, you must make the effort to increase your core body temperature at night. This can be done through exercise, eating protein while on a ketogenic diet, and of course, the most powerful change is through cold exposure adaptation.

Exercise and Thermoregulation

Exercising will increase DHEA, cortisol and energy expenditure. Both DHEA and cortisol are seen in the day time, modulating core body temperature, but neither interrupt melatonin secretions. In fact, exercise has been shown to increase melatonin secretions as well as combat drops in core body temperature.

It may be important to exercise as soon as you wake up from your core sleep if you are extremely cold, or when you are coldest at night.

Protein meal in the middle of the night

Many people who are not used to eating at night will struggle to keep their body temperature high in the middle of the night because they are simply not eating enough at that time.

Protein induces glucogenesis in a ketogenic person, which will increase hypothalamic insulin which will increase core body temperature. Protein also increases cortisol secretion which will help increase energy expenditure and wakefulness.

It may be important to eat a very large protein meal (40-100g protein) as soon as you wake up from your core sleep if you are extremely cold, or when you are coldest at night. It may be beneficial to make this the largest meal of the 24h day for the first few weeks when adapting to a polyphasic schedule so that the thermic effect of protein and thermic effect of food in general increases core body temperature and wakefulness when it is most needed.

Ketogenic Diets and Cold Exposure

Changing to a ketogenic diet will be the greatest dietary change you can make to improve thermoregulation. Cold tolerance is significantly greater when cold-acclimatized animals are also adapted to a ketogenic diet.

If people change into a ketogenic diet too fast, their T3 may drop too quickly and their thyroid stops working correctly. A slow transition into a ketogenic diet is important so those thyroid hormones are kept in balance, as thyroid hormones are important for thermogenesis.

The benefits of timed Cold Exposure on Sleep

There is evidence that if you time the cold exposure correctly that there are great benefits to sleep. It makes sense that cold exposure at night would benefit night sleep because the local temperature will usually be lower at night than in the day.

Mildly cold ambient temperatures increase SWS, and with an increasingly colder exposure, the effect reverses and increases REM sleep. We see a strong link between thermoregulation and the circadian rhythm when correct sleeping habits and cold exposures are experienced daily.

Mild cold exposure and SWS

In support of SWS we see short or mild exposures to cold increase SWS. “The basal forebrain area forms an important sleep and thermoregulation circuit with two nuclei in the hypothalamus, the anterior hypothalamus, and the preoptic area. These three structures and the connections among them constitute the POAH. Evidence that the POAH plays a combined role in these two important processes comes from experiments that indicate that:

a) lesions of the basal forebrain create insomnia, while stimulation creates drowsiness and sleepiness;

b) Warming the POAH induces delta sleep; and

c) POAH nerve firing increases during sleep and in response to an increase in body temperature.” – Source

If we induce warming of the POAH with cold exposure then we will have an increase in delta sleep.

When people become used to sleeping in blankets they lose their ability to respond to cold exposure and therefore require warmer temperatures to sleep soundly. Warmer temperature sleep results in worse sleep quality than acclimatized cold exposed sleep.

Acute exposure to colder than comfortable conditions can increase SWS, while acute exposure to temperatures colder than the body can handle results in a decrease in SWS. When you adapt to sleeping in cold conditions the cold exposure-response changes so that sympathetic nervous activity is small and the SWS will become increased again. This means that when you first start adapting to cold exposure you will have a decrease in sleep quality, but later an increase in sleep quality along with all the other benefits of cold adaptation.

Extended Acute Cold Exposure and REM Sleep

Cold exposure increases THR, which leads to an increase in Thyroid-stimulating hormone (TSH), which leads to an increase in T3, and T3 warms our core body temperature. If we increase our thyroid hormones through cold thermogenesis we can increase hGH, decrease prolactin, increase all the things that support healthy REM. Acute prolactin increases the acute production of DHEA, and “Organisms that produce increased DHEA have an advantage during prolonged cold and darkness; they are warmer” which would suggest that if we are up and about at night, we are meant to be exposed to cold as part of the night time ritual. Not only are we meant to be up at night, but we are also meant to be creating metabolic heat too.

In the second half of the night, we are usually at our coldest, despite REM sleep showing the greatest amount of sympathetic nervous activity. If we are exposed to increasingly colder temperatures throughout the night our heat production should peak by the end of the night instead of the trough. Continued exposure will increase sympathetic nervous activity which will support REM sleep.

Brown Fat Metabolism

Brown fat is a type of fat that is stored inside the body (not the outside) which has mitochondria inside the fat cells. This means brown fat is as active as a muscle and is metabolically efficient. Babies are born with a high amount of brown fat, but as the baby becomes conditioned to modern comforts such as a temperature-controlled environment and a high carbohydrate diet, it loses its brown fat.

Brown adipose tissue is essential for classical nonshivering thermogenesis (this phenomenon does not exist in the absence of functional brown adipose tissue), as well as for the cold acclimation-recruited norepinephrine-induced thermogenesis. When the tissue is active, high amounts of lipids and glucose are combusted in the tissue. And there is an increase in plasma ketone levels and fatty acids in the blood as the body breaks down stored white fat or food fat to fuel the brown fatty tissue.

With continued exposure to cold, it is assumed brown fat stores increase and cold metabolism is therefore made more efficient.

The Cold Exposure Response

When we are exposed to repeated extreme cold, under 10`C (50`F), the body will change its physiology to adapt to that cold. Everyone’s adaptations to cold are different, depending on genes, but everyone is able to adapt to cold because cold-metabolic pathways are built into our ancestor’s genetic structures.

The preliminary response to cold is shivering. When the body realizes the inefficiency of shivering it will change to brown fat metabolism.

How to adapt to cold exposure

There is a method for adapting to cold exposure touted by Jack Kruse.

“CAUTION: If you have a serious health condition, please consult a medical doctor before beginning a CT regimen. Immediately stop treatment if you experience light-headedness or a pale pink to white coloration of the skin.


  • Eat a high fat and/or protein meal (or drink some MCT oil)
  • Immediately drink 16-32oz of ice cold water. DO NOT drink more than 32oz.

What you need: skin thermometer, a timer, ice, and a bathroom sink or larger bowl.

  1. Remove make-up or facial products
  2. Get the water to 10-12`C (50-55`F)
  3. Dunk your face into the ice water and hold as long as you can
  4. Record time and dunk again
  5. Continue for the next two weeks and work your way to using less breaths
  6. DO NOT let your skin temperature fall below 10-12`C (50-55`F)
  1. Lay down flat on your back
  2. Place a 20-40 lbs block of ice on your torso (whilst wearing compression shirt)
  3. Try to extend your time 5 minutes a time until you get to 60 minutes
  4. You will notice your skin is pink to cherry read and numb in places
  5. If you can complete the 60 minutes- remove the compression shirt
    and place the bag of ice directly on the skin

*Note: If you develop cold urticaria at this time, this is a sign you have high levels of tissue and serum omega six content. Stop the experiment and adjust your diet until you have a blood omega six to three ratio that is below 10 to 1 using a ketogenic paleolithic diet.

When you can tolerate the skin being covered for one hour with pink to cherry red skin you’re now ready for the Cold Tub step!


  1. Fill the bathtub with cold tap water
  2. Wear socks, gloves, and a knitted cap to keep the heat in your body
  3. Add 20 lbs of ice to chest and abdomen
  4. When your body is use to the ice you can remove the socks, gloves, and cap
  5. DO NOT let your skin temperature fall below 10-12`C (50-55`F)
  6. Stay for 45 minutes
  7. Continue daily 2-5 times a week
  1. Jump into a pool, lake, or hot tub from the neck down
  2. Stay for 10-20 minutes
  3. Pay attention to skin color


Using Cold Exposure to your Advantage

Cold exposure, as seen above, helps induce SWS and helps wake up. This is explained by the acute vs. chronic reaction against cold exposure. The acute response is a spike of cortisol and an increase in core body temperature, which will wake a person up. The chronic reaction is the increase in POAH nerve firing, which, if someone is asleep, will increase SWS. If someone is awake, the POAH nerve firing will simply not activate the increase in delta activity.

It is recommended that you do a comfortably cold exposure to cold before your dusk core, and an uncomfortably (adaptation-worthy) cold exposure (such as an appropriate step in Jack Kruse’s guide) after you wake up from your dusk core


If we can increase our SWS depth and density in our cores, we will suffer much less from sleep deprivation and require less overall sleep.

If we can increase thermogenesis through cold exposure we can sleep in cooler environments (without blankets) and remove our attachments to our bed (blanket warmth) and therefore rise from bed easier.

If we can increase thermogenesis by exercising, eating protein, and further cold exposure, we will more easily be awake during the night after a dusk core sleep.

Once adapted to cold exposure, timing cold exposure before and after a dusk core sleep will increase SWS and REM and increase post-core temperature control at night, leading to better sleep quality and less sleep deprivation.