The Ultimate Guide to Sleep Well, Beat Insomnia and Wake Up Refreshed
Total Reading Time 23 minutes
(improving your sleep is worth this time investment, believe me)
I tried counting sheep as a kid, but the sheep usually falls asleep before me...
Insomnia is a gross feeder. It will nourish itself on any kind of thinking, including thinking about not thinking.
_ Clifton Fadiman
We all have things that scare us at night and I certainly did. Most days, however, it was not the monsters in the closet nor those hiding under the bed. It was the idea that I would spend hours in bed unable to sleep. With my mind wandering in thoughts about the things that happened, the things that never happened but could have and the other things that cannot ever be.
A conversation between me and my brain would usually look something like this:
Brain : Hey there, trying to sleep?
Me : Ummm, yeah...
Brain : BORING! How about parrots...
Me : What??!
Brain : YES! Parrots! If you had millions of them, you could teach them anything... and send them anywhere! what would you do?
Me : What?! That's not even...
Brain : It's cool though!
Me : I guess.
Brain : So...
Me : I am not responding to that...
Brain : Do you need to go the bathroom?
Me : Nope!
Brain : Are you suuuure?
Me : Dammit! Ok, sure...
Hours later I am still awake, trying to solve problems that exist and, eventually, make up other problems that don't. I was a professional insomniac. And I know, I'm not the only one. According to the National Sleep Foundation, 48% of people living in the US report occasional insomnia while 22% experience it every or almost every night.
We don't need to hear that a lack of sleep causes higher Cortisol or an increase in C-Reactive Protein (CRP, a common marker for inflammation) to be convinced that good sleep is good. When we sleep well, we do everything else better and we've all felt it at least once in our lives. When we wake up feeling refreshed we give better presentations, we are more compassionate and just happy overall.
So here are all the changes I made to sleep like a baby (and not any baby, a baby panda, because that my friend is the top level of sleep and relaxation).
I went from staying awake for more than two hours in bed to getting myself knocked out in less than 10 minutes. And going to sleep faster is only part of the equation.
Remember, the first rule is: do not be stupid. I am not an expert and I do not plan on playing one on the internets, these are the things I have tried and have had the greatest impact on me.
Have you tried putting plants in your room? Wearing red glasses that make you look like a douchebag? Taking a sauna or an extremely cold shower? Here are the ultimate changes that helped me improve the quality of my sleep and wake up feeling like a thousand bucks. The first chapter will contain the changes that had the biggest impact on my sleep quality. Then I will describe my exact sleeping routine and how I deal with less controllable situations like travel.
Start Here: The Little Things with a Big Impact
GREAT SLEEP
NEEDS A FEW LITTLE CHANGES
Minimising lights
Calming the brain
Eating better foods
To begin let us keep things simple. Here are the small habit changes anyone can apply that have had the biggest impact on my sleep quality.
Notice how the quantity of sleep is not the goal here. It is not about how much you sleep but how well you sleep. Ever slept for 11 hours and woke up groggy or instead felt amazing after sleeping for only 7 hours? Exactly! What matters is getting enough deep sleep during the night but I will not go through the technical details nor the biochemistry of sleep.
I experimented by affecting both my environment, meaning what I can control in my surroundings, and my inner state, from both the biochemistry and the psychology. So the main variables that we'll be affecting are: light, food and thoughts (I will talk about exercise too in the next chapter, for now, these are only the 20% that affect 80% of the results). Notice how we will put as much focus on the when (or the timing) as we do on the what and how. Also, we will start by identifying which things to delete or substract before going into which things to add
Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away.
Antoine de Saint Exupery
Obviously, since I've been living in Sweden (where the winter days are short and it barely gets dark at all during the summer) these things can vary with the seasons. To make things simple we can assume that we're in an average day for the rest of this article.
0- Light
When you avoid exposure to artificial light from TV, movie screens, computer screens, phones and bright light, Melatonin starts to get released as the sky gets darker. Melatonin helps your body to sleep and recuperate, shut down the hyperactive monkey brain, allows for neuronal repair, pulls oxygen and needed hormones away from your muscle tissue and other cells, thus making it harder to perform physical activity and easier to sleep. It is much harder to sleep if you do not make enough melatonin [1]. Supplementing with melatonin does not unf
Melatonin production is not only affected by the intensity of light but also by the wavelengths. Blue light (a spectrum of around 420 to 485 nm) is supposed to be predominant during the day, which explains why melatonin production gets affected by it. In [2], it is shown that white LED lighting can be five times more efficient at blocking melatonin production than incandescent light bulbs. An even more creepy fact, shining to the eyes is not necessary, a simple LED light is shown to bring changes in regulating melatonin production, body temperature and the amount of deep sleep [4].
Light is one of the ways your brain makes the difference between day and night. Unfortunately, modern artificial lights fly in the face of natural daily sunlight and natural evening darkness. This can throw your body clock way out-of-whack. From the production of hormones such as cortisol and melatonin or neurotransmitters such as serotonin and GABA, to the pulse rate, the blood pressure, the body temperature or even the activity in our guts, many functions in our body will depend on processes linked to the cycle of the day and known as Circadian Rhythms. As an example, jet lag can disrupt our perception of day and night. And as you might have guessed already, light does as well.
The first thing I changed is my screen lighting. As a computer scientist, most of my time is spent staring at my laptop.
So the first step was to install flux (a software that can reduce the screen's blue light). While I had used flux before, I used to let it start only after sunset. Now, I use it during the whole day, which of course makes my screen look red and eventually ends up in making people think that: either my laptop is broken or that I am a maniac. Careful with this though, if you're a designer you will get your colors mixed up, the good news is, you can disable it in case you need any design. The reason I keep flux on during the whole day and not just during the night (when it's dark) is that getting exposed to blue light during the day is also shown to disrupt the circadian rhythm, a source of blue light needs to have a source of infrared or near infrared light coming from the same direction (which is the case for sunlight for example).
The next screen to take care of was my phone, I installed the Twilight app that acts in a similar way to flux.
Around two to three hours before bed I turn off all the lights. And I usually put on my douchebag glasses (or blue light blockers as known in the biohackers community).
Wait... What If I need to get something done? Or write something? Or just wash the dishes?
Easy, use a source of dim incandescent light or red lights that you can light up in a place a little far from you but just enough so you do not end up in the kitchen instead of your bathroom. Avoid LED lights at all costs. And if you want to go a step further you can use blue light blocking glasses for example: TrueDark and Daywalker glasses by Biohacked. The advantage of using glasses is that they can be useful in uncontrollable environments where you cannot decide which lights to turn on or off (e.g: coffeeshops, street lights, trains, airplanes etc.). This can get you sleepy though so I would not wear blue light blockers if I was driving (it's harder to see with them anyway).
Now here are some light related things you can add to improve your sleep. Getting exposed to natural sunlight is an important factor in maintaining alertness and circadian rhythm. Having a look at the red light while the sun is setting (during which fatty acid metabolism hormones such as leptin and adinopectin tend to rise) can also improve sleep quality.
1- Food
Food quality and timing are a big part of a good night sleep. You might already know that drinking a cup of coffee before bed is not an ideal strategy. Some might say: I have no problem sleeping even if I drink coffee... the truth is, even if you go to sleep fast, caffeine will disrupt your sleep. Remember, the goal is not how fast or how long you sleep, the goal is to sleep good, real good.
So before bed, I avoid every substance that can disrupt my sleep:
I avoid caffeine and caffeine rich foods (coffee, tea, chocolate, energy drinks, yerba maté etc.) in the afternoon.
Other substances I try to avoid are Theobromine and Theophylline (mainly found in Kola and Cacao) around 6 hours before sleep.
Alcohol is another substance that lowers REM sleep, fortunately, I do not drink alcohol anyway. Another suspect compound is Tyramine (a naturally occurring trace amine that can be found in cheese, eggplants and chocolate). Tyramine is shown to increase the production of noradrenaline (which boosts brain activity), however, I do not mind having foods that contain tyramine at dinner unless I'm experiencing headaches [3].
Now, what if I told you that the voice in your head when you're sleeping is not yours?
What if it was the bacteria in your gut having a party?
Sounds too creepy to be true? The gut is sometimes considered as a second brain due to the fact that the microbiome can largely affect our neurochemistry, emotional behaviour and brain physiology [5] [6]. Having a healthy gut prevents your bacteria from disturbing you while you try to sleep. Hence, having a healthy diet that uses real good quality foods instead of its processed low quality alternative and keeping a healthy gut will not just make you achieve your fitness goals but will also help you feel better and sleep better. Another threat to your gut are intestinal parasites which can cause restlessness, a difficulty to rest and affect the central nervous system and block your body from performing its normal sleep routines. Parasites are generally more active during the night and can also be the reason you're not getting deep in your sleep.
Around three hours before bed is when I finish having dinner, then I would drink a cocktail (lovender tea or the baby panda cocktail as we've named it with my roommate) around two hours before bed. My dinner would usually consist of a good source of fat (such as olive oil, olives, almonds, avocados, eggs, walnuts, fish) along with some slow carbs (example: sweet potatoes, chickpeas, lentils) or occasionally some not-so-slow-but-pretty-low carbs (such as rice or quinoa)
To avoid going back and forth to the bathroom at night I make sure to drink around 1h30m prior to bed and have cyclic water intake during the day instead of ingesting a cup of water every now and then.
"Oh, you have so many rules, why are you so strict with yourself?" This is far from being strict and most of the changes I made diet-wise came very gradually. I personally prefer having real foods and being in a state where I am performing better. Plus, if I don't sleep well I will be a douchebag to everyone else, so... let's move on.
The Love-nder Tea (or the Baby Panda Cocktail) Recipe
This cocktail recipe will knock you the hell out :
Lavender (the main ingredient as the name suggests). You can optionally add oat flower and valerian.
Chamomille (or good quality Kava, it works like Chamomille on steroids but does have some side effects on the liver if used too often).
Make sure the water is not at boiling temperature to not ruin the flavonoids in the teas.
After the tea is ready, add a teaspoon of honey with a tablespoon of apple cider vinegar. I do know that honey will help restore glycogen stores during the night [7] and that apple cider vinegar can be beneficial to the gut but I have no idea how these two combined are effective in putting you asleep. One thing I know for sure: it works.
2- Thoughts: Killing the monkey mind and sleeping like a zen baby
Things are about to get cheesy, weird and extremely hipster.
Here's the first trick I use when I go to sleep. Since the goal is not to sleep faster but better and since if I just lie down and relax for about 7 hours I will get at least 80% of the benefits of sleep, I consider this : The goal is not to sleep for seven hours but rather to stay in bed for seven hours, and just relax. Whether I sleep or not, I am just here taking this time to relax and chill.
Now let's get into some deep hipster habits. When I have something important coming up, I usually get a sudden anxiety that prevents me from easily relaxing. In general, on days where I have huge amounts of stress, be it physical or psychological, or even if I'm having something I consider to be important the day after meditation is mandatory before bed. But what if it's too late? Remember it's about sleeping better, not more. For this reason, I would take the time to meditate sometimes for around 3 to 5 minutes just enough time to calm the monkey mind.
The fear of a presentation or a test coming up the next day is not helpful in any way especially if it stops you from getting the most of your night. If this happens, I would start by focusing on relaxing the body as I mentioned earlier and accept the fact that I might not sleep and be Ok with it. The reason being that when we usually try Try not thinking about elephants and your mind starts shouting 'ELEPHANTS! ELEPHANTS!'... What a troll... Resisting thoughts only makes them come back stronger. Accept thoughts and they will fade away, imagine a girl trying to make her jerk boyfriend go away, the easiest way is if she tells him "Let's get married" which will make him disappear into non-existence. Your fears are the same, instead of resisting them try giving them more love, more acceptance, more contentment.
I would avoid things that would cause my brain to start firing such as reading emails, writing or studying. Instead, I might read or listen to either fiction, poetry or anything that would have a sedative effect rather than a stimulating effect.
The Han #Yolo Techniques Okay, so we just talked about how it can be useful to shift focus from trying to sleep to simply relaxing for the next hours. So here are a couple jedi mind tricks to relax :
Alternate nasal breathing: close the left side of your nose using your finger and breathe in from the right side, try to breathe in slowly for around 4 seconds. Then hold your breathe without effort, now close the right side of your nose and breathe out from the left side and hold the lungs while empty for a little while. Follow by breathing in again from the left side, keeping the right side of the nose closed and repeat...
Box breathing: Fancy name, simple concept. Breathe in for around 4-20 seconds, hold your breathe in for around the same amount of time, breathe out slowly for around 4-20 seconds and try to hold the empty lungs for around 4-20 seconds. And, repeat.
While doing any of the above exercises, I also try to go through every part of the body and feel if there is tension, and usually feel it fade away as I breathe out. The goal of course is not to try to make the tension fade away, but to just observe it, accept the fact that it is there, which usually ends up making it fade away. Remember, tension is like a douchebag partner, the more you love them the faster they run away.
Making sure that the breathing is deep by lying on the side instead of the stomach, breathing horizontally (instead of vertically as many of us do) while keeping the shoulders relaxed.
These techniques, or deep breathing in general, will calm your mind and sync the sympathetic and parasympathetic nervous systems giving you an optimal Heart Rate Variability and knocking you out when you least expect it. Simply breathing like this for a long time will not only make you more relax but can also have huge therapeutical and physical benefits. And as I will mention below other things such as using lavender essential oil and magnesium can also have relaxing effects.
My exact routine for Improved Sleep Quality
Now, I'm going to be more detailed about my sleeping routine. However, a sleeping routine starts from the moment you wake up to the moment you go back to sleep again. I am here assuming that this is a perfect day with an average daylight time, meaning that there are things I might skip from time to time and that the sunset time can vary a lot in different areas of the world (such as Uppsala, where I am currently staying).
So, let's start from the start:
Waking up
I try to wake up on my own without using an alarm. The main reason being that a regular alarm does not know where I am in my sleep cycle and will usually disrupt me by waking me up feeling groggy at a point where adenosine is affecting the central nervous system. If I have something that I cannot miss and I have to put an alarm then I would put a late worst case alarm. Otherwise you can use an alarm that mimics the sunrise by gradually increasing light and adding soundscapes of birds and stuff (or eventually an app on your phone that does the same thing).
In an ideal setting my wake up time would usually be around 30 minutes before dawn. Waking up before the daylight as shown in [10] gives a feeling of being protected from predators.
When waking up, the brain and body would get turned on with a sudden rush of Cortisol. The adrenal gland will usually produce about 50% more cortisol at this time. For this reason, having a natural soundscape around, be it the sounds of birds, waterfalls or even moving cars, can reduce the stress response. Another very important hormone is released at this same time. This hormone is VIP (Vasoactive Intestinal Polypeptide) responsible for widening blood vessels, contractility in the heart and breaking down liver glycogen. VIP also relaxes muscles related to bowel movement which means that it is a good idea to head to the bathroom during the two hours after waking up. This is all to say that on of the first things I do is TAGD (Take a Good Dump).
Following that I would usually head for a cold shower and meditate. Optionally have some type of movement associated with breathing in order to increase lymph circulation. Then, to improve blood circulation, I would get myself upside down either through a headstand, handstand, skin the cat on a pull-up bar or any type of inversion.
After this I would get out (again depending on the season) do some lazy stretches or mobility warm-ups while getting exposed to sunlight for at least 5min. Now, I really need to stress this last part: getting enough sunlight is a crucial part to maintaining a normal circadian rythm, so if you find me walking around shirtless in the cold Swedish winter, it is not just because I'm a douchebag, there's a scientific reason too!
The morning is where I usually have my drugs, and by that I mean tea and chocolate. My go-tos are Sencha or Macha for their high L-Theanine content which gives a relaxing feeling alongside the caffeine stimulation. I usually avoid coffee since I metabolise it fast. And in case I'm drinking it I would usually mix it with either ghee, butter or coconut oil.
When I'm making tea I would usually mix it up with a teaspoon of turmeric and a pinch of cayenne pepper to increase the bioavailability of its active components. Aside to that, I would either let a piece of raw cacao melt on my tongue, or just add some cacao powder to the tea or even just straight up munch a couple of cacao beans like a Mayan hipster. I have found that the balanced levels of Theobromine and Caffeine in raw cacao work better for me than coffee, plus cacao makes you happy since it boosts serotonin production (as a sidenote, this assumes that the cacao has not been heated too much and that the Tryptophane in it has not gone missing, Tryptophane is heat volatile so if you're using cacao please don't burn your Tryptophane).
Finally, I would open the room window to improve the air quality in my room and head off to whatever the day has to offer.
Noon
I would usually take a nap after lunch around 1pm-3pm (same principle 30minutes closing eyes trying to relax not trying to fall asleep). Taking it after lunch avoids my sleep from being disrupted by hypoglycaemia.
Sometimes, If I'm feeling a little down after the nap I might take some green tea or Chaga (a mushroom that is very popular in Finland).
Afternoon
I avoid having any coffee at this time. I would still drink green tea or drink Chaga or even eat some chocolate. I would usually stop eating chocolate or drinking tea before 3pm.
There's a peak in protein synthesis, cardiovascular efficiency, muscle repair and the ability to recover in general around 5-6pm. Hence, if I'm going to have some type of intense exercise I would plan it around this time . This also makes sure that my dinner is coupled with an increase in protein synthesis and muscle repair which is hitting two birds with one stone (What a horrible saying that is!). I would totally avoid exercising past 7-8pm since exercising, especially at high intensity, is also shown to shift the Circadian Rhythm.
Then comes the sunset. To sleep even better, this is a good time to take a cold shower (usually preceded by either a hot sauna, a hot bath or a hot shower if I have trained before).
This is also the time where I start limiting any artificial lights. Once the sun sets, or at least 3-2 hours before sleep I would turn all the lights off.
After a cold shower is when I would have my dinner following the rules mentioned above in the food section. An example would be some good sources of fats and minerals, such as fish, eggs, avocados, olive oil, argan oil, coupled with some source of slow carbs such as sweet potatoes, beans, lentils or rice, this can be beneficial in both avoiding hypoglycaemia-induced wake up and increasing water retention. By maintaining a proper circadian rhythm, leptin, a hormone that can shift the body into fatty acid utilisation can shut down the appetite and control food cravings at night.
Setting up the stage for better sleep...
I am now about to set up my room.
Around 2 hours before bed, I would stop any activity that would end up in more stress and cause my brain to start thinking, for example instead of reading a non-fiction book about machine learning I would rather read a fiction book about the story of a sheep traveling in space. I would totally avoid responding to emails, studying or working and would just start chilling around.
Depending on the weather, I would usually leave my room window open as I said before so that there's enough ventilation and would close it around 1-3 hours past sunset.
As per ritual, the lights are now off, or at least dimmed. My douchebag red glasses are now on (those I mentioned in the Light section above), to avoid any nasty extra lights trying to infiltrate my photoreceptors. I would start preparing my bed before going to sleep. I would also try to turn off wi-fi and put my phone on airplane mode.
For my pillow I followed Kelly Starrett's advice for a better neck and shoulder positioning.
Around 1h30m before going to bed is when I would finish drinking the Love-nder tea cocktail (details above).
Usually, I would follow this by some form of deep tissue work especially if I've been working out during the day. This can be either using massage therapy, putting a heavy kettlebell on my quads or some form of foam rolling. It is not only good for faster recovery but it also relieves muscle tension. Alternatively, one could do some light form of stretching accompanied with breathing to relax. Acupuncture is also shown to help with insomnia but I have not tried it yet.
For better air quality I would have some kind of plant in my room such as snake plant, dragon tree, or golden cane palm. These would help release negative ions and turn some of the CO2 into oxygen.
To make the sleeping ritual more interesting, I'd put some lavender essential oil on my pillow or mix it with a carrier oil and apply it directly on my skin. I usually avoid using a diffuser to not impact the air quality of the room.
Another thing that helps with sleep and relaxation and that can be applied on the skin is Magnesium. So, I would spray some Magnesium, using this spray from Ancient Minerals, on my quads or abdomen for improved absorption.
And no ritual is cheesy enough if you do not add some meditation into it. For this reason, and others obviously, I would do some short 3 to 5 minute meditation before going to sleep.
And, now for some fancy time
And by that I mean sleeping time.
There are days where I felt rapid heart rate or a feeling of pounding in my ears mainly due to overtraining which showed an early sign of adrenal fatigue. So to fix mineral imbalances, that in my case were caused by having a lack in electrolytes, I would drink a small cup of water mixed with a teaspoon of a good quality salt. This is also a common problem for people who are trying to get into ketosis and is not getting enough electrolytes.
I get on my right side, my pillow being positioned as mentioned in the previous section. While sleeping in other ways can help you go to sleep faster, the truth is if you're sleeping on your stomach you do not breathe properly, your brain is most likely in fight or flight mode due to your neck position, you are not getting enough deep sleep and causing problems to your spine. If I'm having any thoughts about unicorns on steroids trying to take over the city or any type of thought that would limit my sleep I would simply do some type of breathing as mentioned above to get knocked off and I would not worry about not sleeping, because the goal in the end is to just relax for the amount of hours you have set to relax, if you're awake that's fine as long as you're just lying there and relaxing.
Summing Up
It can be very hard, and sometimes unproductive, to try implementing many habits at once. So an effective strategy could be to focus simply on: turning off the lights, feeding the body with the right fuel, avoiding stimulants and stressors and calming the mind with proper nose breathing. There are days, of course, where I do not follow these rules, days where I do not sleep well, nights where I need to stay awake.. and that's fine. Remember, good sleep is a practice, a habit, something you improve on everyday.
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Would love to hear your thoughts, comments, what worked for you etc.
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Bonus: Evening Snack Recipe
To make this evening snack a.k.a The Slow Food Snack, simply mix the following in a bowl:
Half an avocado.
A tablespoon of a good quality coconut oil or olive oil.
A handful of walnuts, almonds or cashews.
A pinch of good quality sea salt or rock salt.
Some vanilla if available.
A teaspoon of raw fairtrade organic unpasteurized Honey... Why? Because I watched a documentary about bees, and I loved it!
Bonus Tips For Traveling
Having a comfortable sleep mask, such as the Sleep Master (cheesy name, great product), can make a huge difference. While using a sleeping mask is not as good as having complete darkness (fun fact: we also have photoreceptors in our skin) it can be a life saver in places where there is just no way you can turn off the lights or put on window shades.
In an airplane having earplugs or noise canceling headsets can help reduce the stress response from the sounds. The atmosphere in an airplane is usually incredibly dry so you do want to get well hydrated too.
As shown in [11] airplane cabins can be some of the nastiest places to be in. While you cannot do much to control the air quality in there, you can at least make sure that your immune system takes care of intruders and restore your glutathione. Probably munching on garlic before the flight is not an ethical way to do it but at least make sure you avoid things that will hurt your immune system and one of them is the food you get in the airplane. Then you want to get some good sources of Vitamin-C or glutathione precursors such as broccoli sprouts, oranges, lemons, papaya, strawberries, Brussel sprouts etc. (I would avoid juicing them unless in a hurry to not break down the fiber and cause faster oxidation).
When you've arrived at destination try doing some high-intensity workout if possible and get as much sun exposure as possible to reset the circadian rhythm. Walking barefoot on earth is also very effective in resetting your body clock and a good way to get some attention in public spaces.
In a hotel room where there are LED lights that cannot be controlled, dark tape can be used to just hide them.
To avoid sources of fluorescent lights in the morning be it on airplanes or airports you can use a pair of the Daywalker Elite glasses.
References
Scheer, F.A.; Wright, K.P.; Kronauer, R.E.; Czeisler, C.A. (2007). “Plasticity of the intrinsic period of the human circadian timing system”. In Nicolelis, Miguel. PLoS ONE 2 (1): e721.
Falchi, F. & Cinzano, P. & Elvidge, C. & Keith, D. & Haim, A. (2011). Limiting the impact of light pollution on human health, environment and stellar visibility. Journal of Environmental Management 92 (10): 2714–2722.
National Headache Foundation's low Tyramine Diet: http://www.headaches.org/headache-sufferers-diet/
Absence of circadian phase resetting in response to bright light behind the knees. https://www.ncbi.nlm.nih.gov/pubmed/12142528?dopt=Abstract
Indigenous Bacteria from the Gut Microbiota Regulate Host Serotonin Biosynthesis http://www.cell.com/cell/fulltext/S0092-8674(15)00248-2
Eight year prognosis of postinfectious irritable bowel syndrome following waterborne bacterial dysentery http://gut.bmj.com/content/59/5/605
Effect of honey on nocturnal cough and sleep quality: a double-blind, randomized, placebo-controlled study. https://www.ncbi.nlm.nih.gov/pubmed/22869830
Mednick, S. & Nakayama, K. & Stickgold, R. (2003). Sleep-dependent learning: a nap is as good as a night. Nature Neuroscience http://www.nature.com/neuro/journal/v6/n7/full/nn1078.html
Scheer, F. & Buijs, R. (1999). Light affects morning salivary cortisol in humans. The Journal of Clinical Endocrinology & Metabolism 84 (9): 3395–3398.
Light affects morning salivary cortisol in humans. https://www.ncbi.nlm.nih.gov/pubmed/10487717
Health Effects Associated with Exposure to Airliner Cabin Air https://www.ncbi.nlm.nih.gov/books/NBK219002/
Montakab, H. (1999). acupuncture and insomnia Forsch Komplementarmed. , February(6), S29-31