“Early to bed and early to rise makes a man healthy, wealthy, and wise.” — Benjamin Franklin

Have you heard of this quote before? If not, perhaps you should study it! Sleep is one of the most essential things to human health and survival, just as much as nutrition and hydration. I’m sure you know this, as common sense will tell you that sleep is essential.

Yet, even with this understanding, many people put sleep on the backburner in modern society, considering it not very important. This is especially increasing with the “go-go-go” attitude of our culture.

On the other hand, there are people who do know the importance of sleep yet can’t sleep very well due to insomnia or other issues. And with these two main chunks of people, along with others, the reality is that many people in the modern world are not getting enough sleep, and nearly everyone is suffering from suboptimal sleep quality too, even for those seemingly getting enough hours.

Sleep Requirements

Sleep needs differ pretty significantly among different age groups, but for adults (the age group most often reading this page), the recommendation is 7 to 9 hours. Yet, over 35 % of adults get less than 7 hours per night (1). Furthermore, over 50 million American adults suffer from sleep disorders, the majority of which is insomnia (30 million people) (2).

These are some massive numbers, but they don’t even pain the whole picture. Primarily, this is because even for people without sleep problems, most others are also getting suboptimal sleep due to all of the factors in today’s society. Even if you feel pretty refreshed and energized after sleeping, I can almost guarantee that you could improve your sleep.

Problems Stemming from Lack of Sleep

And trust me, you should want to do that! A lack of sleep is related to so many health issues, including obesity and metabolic issues; declined cardiovascular health and increased cardiovascular disease risk; increased inflammation, depression, anxiety, and other psychological problems; diabetes; decreased athletic performance; lower cognitive functioning,  declined hormonal health (e.g. testosterone); and  a higher propensity to engage in unhealthy behaviors, such as eating unhealthy foods and using higher amounts of drugs and alcohol (3,4,5,6,7)

All of this shouldn’t be too surprising. After all, its easy to gauge how you feel after a bad night’s sleep. And if this continues over a long period of time, that is where the main effects happen. Unless you’re in the tiny minority who only need 4 or 5 hours per night, you should probably try to sleep more, and, more importantly, improve the quality of your sleep. To do so is associated with improvements in pretty much all of the health areas I just mentioned.

What to Do About It

Luckily, improving your sleep quality and perhaps quantity, is very straightforward. You just have to be willing to counteract a lot of the factors involved in modern society and return to a more natural lifestyle.

 The steps listed below are highly researched points and should be able to improve your sleep. Some of these may be familiar, but my guess is most will be somewhat new to you. Regardless, take a close look at how to implement these, and if you do so, you’ll be on your way to better sleep and ultimately better health.

Light Exposure

One important factor to make sure you implement is how and when you’re exposed to light. Many of the body’s natural processes, including sleep, are regulated by the circadian rhythm, which is essentially the body’s internal clock. And one very important influence on this circadian rhythm is light. Other influences are temperature, exercise, and food intake (all discussed later).

 In a natural environment, one is exposed to sunlight in the morning and throughout the day, and of course, darkness at night. This pattern leads to optimal sleep and then optimal energy levels throughout the day (8,9). Thus, in order to optimize sleep quality, you need to try to replicate this as close as possible.

Get Morning and Afternoon Sunlight

So, firstly, aim to get at least 5 minutes of direct sunlight exposure as early as possible after you wake up. The more time the better. Doing so sends a signal to your body that it is daytime, and it also leads to the production of serotonin, which will eventually turn into melatonin at night, helping you to sleep better.

In the afternoon, sunlight exposure further increases serotonin and provides you with vitamin D, which has a role in the regulation of sleep. Aim for at least 10 minutes in the afternoon, preferably 20 or more minutes. Research has shown that sunlight improves mood, well-being, and sleep, and those who get more sunlight typically sleep better (10, 11).

Limit (Ideally, Eliminate) Artificial Light at Night

Along with the first tip, you also must eliminate artificial light at night, mainly coming from televisions, phones, and laptops because these have more blue light, although lightbulbs do as well. Remember how serotonin will turn into melatonin? Well, that only happens in darkness. Without darkness, the body has no cue that it is nighttime, so if you’re exposing yourself to light at night, you will be drastically reducing melatonin levels, and probably increasing cortisol, both of which hinder sleep (12).

Now, melatonin may help with falling asleep, but its more important role is sleep quality. So, even if you fall asleep easily after using electronics/technology at night, the fact is that your sleep quality could definitely be improved. So, to do this, either eliminate electronics at night, or wear blue-light blocking glasses. Sure, they may look weird, but the benefits are worth it. Plus, eliminating electronics at night is less stimulating, which also will improve sleep. Blue-light glasses are very effective for correcting sleep disorders, especially delated sleep phase, and they are associated with higher levels of melatonin and lower nighttime cortisol levels (13).

Overall, these two tips together will help you to align your body with its natural rhythm. The chances are high that you aren’t doing either of these, let alone both of these things, so I would start here before you do anything else. This should also be combined with waking up and going to bed at roughly the same time each day to maintain this rhythm and so the light cues are coming in at the same times.

Optimize Your Bedroom Environment

The next set of tips related to sleep improvement are about optimizing your bedroom environment. Essentially, you want to sleep in a cool, comfortable, dark, quiet, and well-ventilated room.

Cool Temperature

Temperature also has an influence on the circadian rhythm and thus sleep. The body naturally cools down at night and reaches it’s lowest temperature in the middle of the night. However, excessively hot rooms disrupt this process. This might be no surprise if you’ve ever gone without air conditioning in the summer. Cold temperatures can also negatively affect sleep as well. Thus, you need to sleep in a room that is comfortable for you.

A recent review shows that comfortable temperatures are related to longer sleep and increased sleep quality, and that the temperature of the bedroom and the bed itself should be cool (15). There is a range of optimal temperatures, but generally it should be 60 to 67 degrees (16). This will vary from person to person, so adjust accordingly to best fit your needs.

Block Light During Sleep

Just as you should block light or eliminate it before sleep, you should also try to make your room as dark as possible. Bedside light and other incoming light are associated with poorer sleep quality, as well as disrupted sleep (i.e. more frequent awakenings) (17). The best way to do this is to wear a sleep mask and/or use blackout curtains. These tips are especially useful for when you’re traveling and there is a lot of light that you’re not used to.

Quiet is Key

You should also make your room as quiet as possible. To do this, use a white noise machine or a fan to block out random noises, and consider wearing earplugs. And if you’re partner is someone who snores loudly, seriously consider getting separate bedrooms or beds. Together, the combination of blocking out light and sound at night improves sleep tremendously (18), even in people in intensive care units, who are subject to many negative environmental factors that could otherwise disrupt sleep (19).

Ventilation

You should also make sure that your bedroom is well-ventilated. Excess CO2 buildup can disturb sleep, whereas fresh air can improve sleep (20). Simply opening a window during the day and throughout the night can improve air quality (unless you live in a highly polluted environment). In turn, having a window open should improve sleep quality and next-day performance (21).

Comfort

Lastly, your bed needs to be comfortable (yeah, duh!) It turns out that there has been research on bed quality, and subjective ratings of mattress comfort are related to sleep outcomes. Simply, sleeping on a comfortable mattress should lead to higher sleep efficiency and greater levels of deep sleep (22). If you’ve gone a while without buying a new mattress and/or your current one is uncomfortable, I highly recommend that you switch it out for a better mattress. (I hope) you spend at least 1/3^rd of your life on it, so it is a worthwhile investment.

Nutritional Factors

Diet and nutrition are also intertwined with sleep. It shouldn’t really come as a surprise that a healthier diet is associated with better sleep, but there are some key factors in particular to pay attention to.

The Best Nutritional Foods for Sleep

While a healthy diet supports sleep, there are some key players that will have the most bang for your buck. These include seafood, organ meats, and bone broth or bone products. Seafood is very high in healthy fatty acids, which should promote sleep, especially EPA and DHA Omega-3, and they are high in zinc, all of which are necessary for proper stress reactivity and sleep (23).

Organ meats, especially liver, have loads of the B-vitamins and phosphatidylserine, both of which are important for managing stress and should improve sleep (reference listed in below section [34]).

In addition, bone broth, collagen, and gelatin should be consumed because they contain a high amount of glycine, which is known for its relaxing properties, and can improve sleep (24). Many people do not consume nearly enough of this compound due to eating mainly muscle meat, so eating these proteins can help to create balance.

Meal Timing and Macronutrient Intake

You should also eat at specific periods of the day, and have certain foods at certain times. Essentially, you should avoid eating three hours before bed because this will improve sleep quality, in part by enhancing the release of serotonin, melatonin, and growth hormone. Contrarily, eating right before bed, especially high-calorie foods, impairs sleep quality and quanity (25).

You should also eat meals at approximately the same time each day because consistent meal timing aligns with the circadian rhythm and improves sleep, whereas shifting meals hinders sleep (26).

Also, you should consume protein and fats earlier in the day, along with a balanced meal of protein, fats, and carbohydrates later in the day. Doing these things aligns with the body’s natural rhythms and should also promote healthy levels of serotonin and melatonin, which ultimately helps you to calm down and sleep better (27,28). Don’t be afraid to consume carbohydrates, especially with dinner, as long as they are healthy, such as sweet potatoes.

Supplement with Magnesium and (maybe) Zinc

Even if you have a high quality diet, you still may be deficient in magnesium and zinc, especially magnesium. Now, magnesium is a crucial mineral because it helps to regulate the stress response, leads to the production of GABA in the brain, and is associated with alpha-wave brain activity, all of which are interrelated with sleep (29).

If you have low magnesium, your chances of insomnia and sleep problems are much higher, so you definitely should supplement. The best forms are magnesium glycinate and magnesium l-threonate. The latter is more expensive, but it crosses the blood-brain barrier and is more absorbable. Regardless, magnesium supplementation should reduce stress and improve sleep (30).

Lastly, consider supplementing with zinc if you don’t eat much seafood or red meat and/or you exercise a lot. (As a related side note, athletes are often zinc deficient because of heavy exercise). The best form to take is zinc picolinate, as it is the most easily absorbed. Zinc is also important for reducing stress and may improve sleep quality and reduce sleep disturbances (31).

Other Supplements to Try

There are massive amounts of sleep supplements on the market, but there are really only a handful that are beneficial. These include magnesium and zinc, along with the below supplements. There are a few more, so this isn’t an exhaustive list, but it’s a good place to start.

L-theanine

L-theanine is an amino acid, naturally occurring in green tea. It is known for its calming properties, specifically because it can increase alpha-wave brain activity and should increase GABA levels in the brain. L-theanine is strongly associated with a reduction in stress and anxiety levels, so it is particularly helpful to take on stressful days (32). It also improves sleep quality and sleep duration significantly (33). I wouldn’t recommend taking it every day because even though it’s not addictive, a tolerance might build up. If you find success in taking it every day, that’s fine, but try to cycle it if you can.

Phosphatidylserine

You should also consider phosphatidylserine because this compound is very effective at reducing stress. Now, it is found in high amounts in organ meats and some seafood, but if you’re not eating those foods on a consistent basis, I highly recommend phosphatidylserine supplementation to reduce stress and improve sleep (34).

CBD

Unless you live under a rock, you’ve also heard about CBD. It has a range of purported benefits, although some still need to be researched thoroughly. However, there is a decent amount of research for CBD on sleep, plus plenty of anecdotal evidence. CBD acts on the endocannabinoid system in the body and therefore may lead to relaxation or mild sedative effects, along with other benefits.

A recent clinical review showed that CBD is often effective for improving sleep quality and duration, minimizing sleep disturbances, and decreasing the time it takes to fall asleep, although higher quality studies are needed to fully highlight the benefits (35). If you can afford it, I recommend trying CBD for a few weeks at least to see if it has an effect on you. Pay close attention to dosages because it can lead to increased alertness in some cases, so you want to be sure you’re taking the right dose at the right time of the day.

Exercise

Unsurprisingly, I also recommend that you exercise in order to improve sleep. Exercise is related to sleep in so many different ways, and it is known that exercising during the day can improve sleep quality, decrease sleep apnea and its related problems, and is positively related with subjective sleep quality, and decreases the time it takes to fall asleep (36).

While any exercise is likely beneficial, current recommendations for exercise to improve sleep center around the typical 150 minutes of moderate exercise per week or 75 minutes of intense exercise per week, or a combination. Strength training twice per week also appears to be good for improving sleep. Make sure to not exercise too hard and/or too often because this will increase stress and in turn negatively affect sleep.

As for what time of day, there actually is not much of a difference between morning, afternoon, or evening exercise, with one exception. Vigorous exercise less than one hour before bed appears to disrupt sleep, so if you still want to exercise at night, make sure you finish it two hours or more before bed (37). While this is anecdotal, most people find morning or afternoon exercise to be the most beneficial, potentially because this aligns most with circadian tendencies.

Drugs and Alcohol

A number of drugs and compounds also affect sleep, but I will focus on the three most common ones used in modern society, of course being caffeine, alcohol, and nicotine. As a whole, nicotine, alcohol, and caffeine are a number of sleep disturbances and suboptimal sleep quality, which in turn increase the risk for substance use, so these really need to be monitored carefully (38).

Nicotine

First, nicotine should not be used within a few hours before sleep because it has a stimulating effect. Yes, some people use it to relax, but the effects of nicotine are actually stimulating on the body, even if it is not consciously realized, and can disrupt sleep (39). I recommend stopping using nicotine-based products at least five hours before sleep.

Alcohol

Second, alcohol consumption should be stopped a couple of hours before sleep. Many people drink alcohol close to bedtime for a number of reasons, one being that it helps them to relax and fall asleep. However, even if you fall asleep more quickly, your sleep quality will suffer, mainly by a decrease in REM sleep (40). If you do drink, try to stop at least two hours before bedtime.

Caffeine

Lastly, caffeine intake needs to be moderated, and eliminated for some people. Caffeine’s effects work by acting on the adenosine receptors in the brain, promoting feelings of wakefulness. However, higher caffeine intake, especially within 6 hours of bedtime, is associated with decreased sleep quality and more frequent awakenings, and higher arousal. (41).

Also, people metabolize caffeine at different rates, so for those most sensitive to caffeine, they might have to cut it out 12 hours or more before bedtime, or not drink it at all, whereas those who metabolize it more quickly can consume it until 8 hours before bedtime. Regardless, it is not optimal for anyone to consume caffeine within 8 hours before bed.

Cognitive Behavioral Therapy

One potentially massive way to improve sleep, especially for those who suffer from insomnia, is cognitive behavioral therapy (CBT). A lot of times, people who struggle with sleep have distorted cognitions, especially in the case of insomnia. These people worry about not sleeping enough, and may do so all throughout the day, and they believe that they have to try so hard to fall asleep because they’re usually not able to. They begin to associate their bed with problems and racing thoughts, and eventually believe that they can’t sleep no matter what.

In turn, they try harder and harder to sleep, but this only makes the problems worse because sleep happens only when you don’t try to do it. They may go to bed even earlier to try to fall asleep during a longer period of time, and stay in bed even if they’re not sleeping, but this only feeds to the issues. And they also may ridicule themselves after not sleeping well, continuing the cycle.

If you identify with this, you should make this tip your highest priority. This is because it doesn’t matter if you do everything else right; your sleep will still suffer if you worry about sleep itself. You can eat the best diet in the world and do all of the other right things, but if all of that is due to a worry about sleep, then you have the wrong mindset and need to correct it.

Thankfully, CBT corrects these biased thoughts and behaviors. Through CBT, the patient is able to correct their dysfunctional thoughts, and behaviors mainly by realizing that they can sleep like other healthy people, and that they do not have to try to fall asleep, but rather should just let it happen. Furthermore, they learn to spend only the amount of time in bed that they are sleeping, and they also learn to practice many other healthier sleep behaviors and sleep hygiene practices, and can eventually re-associate the bed with relaxation and sleep. This takes some time, but CBT and similar therapies are highly effective for treating insomnia and its related problems, such as depression (42,43,44).

Wind Down and Buffer Stress, Especially in the Evening

Stressful events during the day will obviously have a negative effect on sleep. Yet there are a number of things you can do to mitigate these consequences, such as socialization, meditation, yoga, and gratitude/journaling.

Mindfulness Meditation

Mindfulness meditation has many benefits, most of which I wrote recently about in my previous article. Through this, one learns to focus on the present moment and be much more accepting, which drastically reduces stress and improves health. Mindfulness meditation can also therefore target key cognitive and emotional disruptions that are common in sleep disorders, such as rumination, overthinking, self-criticism, and anxiety (45).  It is no surprise, then, that this practice is highly effective for improving sleep quality and reducing sleep disturbances, especially during periods of stress (46). Shoot for just 5 minutes per day at first, and you can do it up to however long you want over time. You can also practice mindfulness meditation “in motion” by doing some light yoga, which is great for improving psychological health and sleep (47).

Socialization

Isolation is a key risk factor for many negative mental and physical health outcomes, and it also leads to suboptimal sleep (48). This is especially true when someone faces a highly stressful day, in that they won’t have anyone to turn to cope with their problems, leading to increased stress and impaired sleep. A giant meta-analysis shows a strong positive relationship between social support and sleep quality, and that social support appears to directly buffer stress, leading to improved sleep (49). Thus, take time to talk and interact with loved ones each day, see your friends often, and so forth. The effects will be even greater with physical contact because this will further decrease stress, so go hug someone!

Gratitude and Reflection Journal

Another key way to buffer stress and improve sleep is through journaling at the end of the day, particularly with a focus on gratitude. Negative thoughts and emotions negatively impact sleep, but focusing on gratitude directly changes your thoughts to more positive ones, thereby reducing stress and anxiety (50). Most likely then, gratitude becomes especially important on the days where you don’t feel as good, and where you forget about all of the good things.

Focusing on the things you’re grateful for is a great way to end the day, and research shows that it improves sleep quality and sleep duration, largely because of its ability to generate positive pre-sleep thoughts and emotions (51). So to do this, simply write three things you’re grateful for. And you can also further enhance your journal by writing three things that went well, three things you can work on, and a plan for the next day. All of this allows you to get the thoughts on paper and should eliminate or greatly reduce nighttime rumination.

Music

Finally, listening to music is a great way to end the day and improve sleep. Like some of these other tips, listening to music decreases rumination and increases feelings of positivity and well-being. In turn, listening to music before bed appears to correct certain sleep disorders and should improve sleep in the general population as well (52). I wouldn’t recommend anything too stimulating, but you can pick pretty much anything as long as you enjoy it.

That’s a Wrap

And there you have it. If you’ve made it through, congratulations because you now have a much higher understanding of how to improve your sleep. And really, there are many other things you can do too, but these are definitely the most important ones that you should focus on first.

As a final word, you must also realize that the degree to which these factors will have a positive effect on you is highly individualized, and thus people will have different hierarchies of importance. For example, take someone who is very easy-going, falls asleep easily, yet also watches T.V. at night, and eats a rather unhealthy diet. This person should focus first on correcting their unhealthy behaviors, which would likely improve sleep quality.

As an extreme opposite, let’s say someone else eats a perfect diet, uses blackout curtains and other things to make their room ideal for sleeping; exercises, winds down, etc., yet they are really neurotic and easily stressed out. For this person, the first thing to focus on is CBT along with stress-reducing supplements and activities.

As you can see, it is always individualized, so take the time to understand the areas where you should focus on first. Once you’ve done that, you’ll be well on your way to better sleep and a healthier life.

References

1. Khubchandani, J., & Price, J. H. (2020). Short Sleep Duration in Working American Adults, 2010–2018. Journal of Community Health, 45(2), 219-227. https://doi.org/10.1007/s10900-019-00731-9

2. University of Pennsylvania School of Medicine. (2018). One in four Americans develop insomnia each year: 75 percent of those with insomnia recover. ScienceDaily. Retrieved October 28, 2020 from www.sciencedaily.com/releases/2018/06/180605154114.htm

3. Hamilton, N.A., Nelson, C.A., Stevens, N. et al. Sleep and psychological well-being. Soc Indic Res 82, 147–163 (2007). https://doi.org/10.1007/s11205-006-9030-1

4. Freeman, D., Sheaves, B., Goodwin, G. M., Yu, L. M., Nickless, A., Harrison, P. J., … & Hinds, C. (2017). The effects of improving sleep on mental health (OASIS): a randomised controlled trial with mediation analysis. The Lancet Psychiatry, 4(10), 749-758. https://doi.org/10.1016/S2215-0366(17)30328-0

5. Grandner M. A. (2018). The Cost of Sleep Lost: Implications for Health, Performance, and the Bottom Line. American journal of health promotion : AJHP, 32(7), 1629–1634. https://doi.org/10.1177/0890117118790621a

6. Luyster, F. S., Strollo, P. J., Jr, Zee, P. C., Walsh, J. K., & Boards of Directors of the American Academy of Sleep Medicine and the Sleep Research Society (2012). Sleep: a health imperative. Sleep, 35(6), 727–734. https://doi.org/10.5665/sleep.1846

7. Copinschi, G. (2005). Metabolic and endocrine effects of sleep deprivation. Essential psychopharmacology, 6(6), 341-347. https://pubmed.ncbi.nlm.nih.gov/16459757/

8. Prayag, A. S., Münch, M., Aeschbach, D., Chellappa, S. L., & Gronfier, C. (2019). Light modulation of human clocks, wake, and sleep. Clocks & sleep, 1(1), 193-208. https://doi.org/10.3390/clockssleep1010017

9. Blume, C., Garbazza, C., & Spitschan, M. (2019). Effects of light on human circadian rhythms, sleep and mood. Somnologie : Schlafforschung und Schlafmedizin = Somnology : sleep research and sleep medicine, 23(3), 147–156. https://doi.org/10.1007/s11818-019-00215-x

10. Dautovich, N. D., Schreiber, D. R., Imel, J. L., Tighe, C. A., Shoji, K. D., Cyrus, J., … & Dzierzewski, J. M. (2019). A systematic review of the amount and timing of light in association with objective and subjective sleep outcomes in community-dwelling adults. Sleep health, 5(1), 31-48. https://doi.org/10.1016/j.sleh.2018.09.006

11. Aulsebrook, A. E., Jones, T. M., Mulder, R. A., & Lesku, J. A. (2018). Impacts of artificial light at night on sleep: a review and prospectus. Journal of Experimental Zoology Part A: Ecological and Integrative Physiology, 329(8-9), 409-418. https://doi.org/10.1002/jez.2189

12. Tähkämö, L., Partonen, T., & Pesonen, A. K. (2019). Systematic review of light exposure impact on human circadian rhythm. Chronobiology international, 36(2), 151-170. https://doi.org/10.1080/07420528.2018.1527773

13. Shechter, A., Quispe, K. A., Mizhquiri Barbecho, J. S., Slater, C., & Falzon, L. (2020). Interventions to reduce short-wavelength (“blue”) light exposure at night and their effects on sleep: A systematic review and meta-analysis. Sleep Advances.

14. Okamoto-Mizuno, K., & Mizuno, K. (2012). Effects of thermal environment on sleep and circadian rhythm. Journal of physiological anthropology, 31(1), 14. https://doi.org/10.1186/1880-6805-31-14

15. Lan, L., Tsuzuki, K., Liu, Y. F., & Lian, Z. W. (2017). Thermal environment and sleep quality: A review. Energy and Buildings, 149, 101-113. https://doi.org/10.1016/j.enbuild.2017.05.043

16. Pacheco, D. & Wright, H. (2020). The best temperature for sleep. https://www.sleepfoundation.org/bedroom-environment/best-temperature-for-sleep#:~:text=The%20best%20bedroom%20temperature%20for,for%20the%20most%20comfortable%20sleep.

17. Cho, J. R., Joo, E. Y., Koo, D. L., & Hong, S. B. (2013). Let there be no light: the effect of bedside light on sleep quality and background electroencephalographic rhythms. Sleep medicine, 14(12), 1422-1425. https://doi.org/10.1016/j.sleep.2013.09.007Get rights and content

18. Kim, G. M., & Kim, E. J. (2017). The Effects of White Noise on Sleep Quality, Depression and Stress in University Students. Journal of Korean Academic Society of Home Health Care Nursing, 24(3), 316-324. https://doi.org/10.22705/jkashcn.2017.24.3.316

19. Locihová, H., Axmann, K., Padyšáková, H., & Fejfar, J. (2018). Effect of the use of earplugs and eye mask on the quality of sleep in intensive care patients: a systematic review. Journal of sleep research, 27(3), e12607. https://doi.org/10.1111/jsr.12607

20. Liao, C., Delghust, M., & Laverge, J. (2019, April). Association between Indoor Air Quality and Sleep Quality. In 33rd Annual Meeting of the Associated-Professional-Sleep-Societies (SLEEP) (Vol. 42). Oxford Univ Press Inc. https://www.aivc.org/sites/default/files/D2_S7A-01_1.pdf

21. Strøm‐Tejsen, P., Zukowska, D., Wargocki, P., & Wyon, D. P. (2016). The effects of bedroom air quality on sleep and next‐day performance. Indoor Air, 26(5), 679-686. https://doi.org/10.1111/ina.12254

22. Lee, H., & Park, S. (2006). Quantitative effects of mattress types (comfortable vs. uncomfortable) on sleep quality through polysomnography and skin temperature. International journal of industrial ergonomics, 36(11), 943-949. https://doi.org/10.1016/j.ergon.2006.07.007

23. Ji, X., Grandner, M. A., & Liu, J. (2017). The relationship between micronutrient status and sleep patterns: a systematic review. Public health nutrition, 20(4), 687-701.

https://doi.org/10.1017/S1368980016002603

24. Kawai, N., Sakai, N., Okuro, M., Karakawa, S., Tsuneyoshi, Y., Kawasaki, N., Takeda, T., Bannai, M., & Nishino, S. (2015). The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleus. Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology, 40(6), 1405–1416. https://doi.org/10.1038/npp.2014.326

25. Crispim, C. A., Zimberg, I. Z., dos Reis, B. G., Diniz, R. M., Tufik, S., & de Mello, M. T. (2011). Relationship between food intake and sleep pattern in healthy individuals. Journal of clinical sleep medicine : JCSM : official publication of the American Academy of Sleep Medicine, 7(6), 659–664. https://doi.org/10.5664/jcsm.1476

26. Wehrens, S., Christou, S., Isherwood, C., Middleton, B., Gibbs, M. A., Archer, S. N., Skene, D. J., & Johnston, J. D. (2017). Meal Timing Regulates the Human Circadian System. Current biology : CB, 27(12), 1768–1775.e3. https://doi.org/10.1016/j.cub.2017.04.059

27. Peuhkuri, K., Sihvola, N., & Korpela, R. (2012). Diet promotes sleep duration and quality. Nutrition research, 32(5), 309-319. https://doi.org/10.1016/j.nutres.2012.03.009

28. Binks, H., E Vincent, G., Gupta, C., Irwin, C., & Khalesi, S. (2020). Effects of diet on sleep: A narrative review. Nutrients, 12(4), 936. https://doi.org/10.3390/nu12040936

29. De Baaij, J. H., Hoenderop, J. G., & Bindels, R. J. (2015). Magnesium in man: implications for health and disease. Physiological reviews. doi: 10.1152/physrev.00012.2014.

30. Nielsen, F. H. (2015). Relation between magnesium deficiency and sleep disorders and associated pathological changes. In Modulation of Sleep by Obesity, Diabetes, Age, and Diet (pp. 291-296). Academic Press. https://doi.org/10.1016/B978-0-12-420168-2.00031-4

31. Cherasse, Y., & Urade, Y. (2017). Dietary zinc acts as a sleep modulator. International journal of molecular sciences, 18(11), 2334. https://doi.org/10.3390/ijms18112334

32. Williams, J. L., Everett, J. M., D’Cunha, N. M., Sergi, D., Georgousopoulou, E. N., Keegan, R. J., … & Naumovski, N. (2020). The effects of green tea amino acid L-theanine consumption on the ability to manage stress and anxiety levels: A systematic review. Plant Foods for Human Nutrition, 75(1), 12-23.

33. Kim, S., Jo, K., Hong, K. B., Han, S. H., & Suh, H. J. (2019). GABA and l-theanine mixture decreases sleep latency and improves NREM sleep. Pharmaceutical biology, 57(1), 64-72. https://doi.org/10.1080/13880209.2018.1557698

34. Komori, T. (2015). The effects of phosphatidylserine and omega-3 fatty acid-containing supplement on late life depression. Mental illness. https://doi.org/10.1108/mi.2015.5647

35. Kuhathasan, N., Dufort, A., MacKillop, J., Gottschalk, R., Minuzzi, L., & Frey, B. N. (2019). The use of cannabinoids for sleep: A critical review on clinical trials. Experimental and clinical psychopharmacology, 27(4), 383. https://doi.org/10.1037/pha0000285

36. Kelley, G. A., & Kelley, K. S. (2017). Exercise and sleep: a systematic review of previous meta‐analyses. Journal of Evidence‐Based Medicine, 10(1), 26-36. https://doi.org/10.1111/jebm.12236

37. Stutz, J., Eiholzer, R., & Spengler, C. M. (2019). Effects of evening exercise on sleep in healthy participants: A systematic review and meta-analysis. Sports Medicine, 49(2), 269-287. https://doi.org/10.1007/s40279-018-1015-0

38. Garcia, A. N., & Salloum, I. M. (2015). Polysomnographic sleep disturbances in nicotine, caffeine, alcohol, cocaine, opioid, and cannabis use: a focused review. The American Journal on Addictions, 24(7), 590-598. https://doi.org/10.1111/ajad.12291

39. Guimarães, K., & Roque, A. C. (2019). Influence of nicotine and alcohol on sleep and implications on insomnia: the reward-attention circuit model. arXiv preprint arXiv:1902.05515.

40. Hu, N., Ma, Y., He, J., Zhu, L., & Cao, S. (2020). Alcohol consumption and incidence of sleep disorder: A systematic review and meta-analysis of cohort studies. Drug and Alcohol Dependence, 108259.

41. Clark, I., & Landolt, H. P. (2017). Coffee, caffeine, and sleep: A systematic review of epidemiological studies and randomized controlled trials. Sleep medicine reviews, 31, 70-78. https://doi.org/10.1016/j.smrv.2016.01.006

42. Sharma, M. P., & Andrade, C. (2012). Behavioral interventions for insomnia: Theory and practice. Indian journal of psychiatry, 54(4), 359. https://www.indianjpsychiatry.org/text.asp?2012/54/4/359/104825

43. Thakral, M., Von Korff, M., McCurry, S. M., Morin, C. M., & Vitiello, M. V. (2020). Changes in dysfunctional beliefs about sleep after cognitive behavioral therapy for insomnia: A systematic literature review and meta-analysis. Sleep Medicine Reviews, 49, 101230. https://doi.org/10.1016/j.smrv.2019.101230

44. Ebben, M. R., & Narizhnaya, M. (2012). Cognitive and behavioral treatment options for insomnia. Mount Sinai Journal of Medicine: A Journal of Translational and Personalized Medicine, 79(4), 512-523. https://doi.org/10.1002/msj.21320

45. Rusch, H. L., Rosario, M., Levison, L. M., Olivera, A., Livingston, W. S., Wu, T., & Gill, J. M. (2019). The effect of mindfulness meditation on sleep quality: a systematic review and meta-analysis of randomized controlled trials. Annals of the New York Academy of Sciences, 1445(1), 5–16. https://doi.org/10.1111/nyas.13996

46. Winbush, N. Y., Gross, C. R., & Kreitzer, M. J. (2007). The effects of mindfulness-based stress reduction on sleep disturbance: a systematic review. Explore, 3(6), 585-591. https://doi.org/10.1016/j.explore.2007.08.003

47. Balasubramaniam, M., Telles, S., & Doraiswamy, P. M. (2013). Yoga on our minds: a systematic review of yoga for neuropsychiatric disorders. Frontiers in PSYCHIATRY, 3, 117. https://doi.org/10.3389/fpsyt.2012.00117

48. Griffin, S. C., Williams, A. B., Ravyts, S. G., Mladen, S. N., & Rybarczyk, B. D. (2020). Loneliness and sleep: A systematic review and meta-analysis. Health psychology open, 7(1), 2055102920913235. https://doi.org/10.1177/2055102920913235

49. Kent de Grey, R. G., Uchino, B. N., Trettevik, R., Cronan, S., & Hogan, J. N. (2018). Social support and sleep: A meta-analysis. Health Psychology, 37(8), 787. doi: 10.1037/hea0000628

50. Jans-Beken, L., Jacobs, N., Janssens, M., Peeters, S., Reijnders, J., Lechner, L., & Lataster, J. (2020). Gratitude and health: An updated review. The Journal of Positive Psychology, 15(6), 743-782. https://doi.org/10.1080/17439760.2019.1651888

51. Wood, A. M., Joseph, S., Lloyd, J., & Atkins, S. (2009). Gratitude influences sleep through the mechanism of pre-sleep cognitions. Journal of psychosomatic research, 66(1), 43-48. https://doi.org/10.1016/j.jpsychores.2008.09.002

52. Dickson, G. T., & Schubert, E. (2020). Music on Prescription to Aid Sleep Quality: A Literature Review. Frontiers in psychology, 11, 1695. https://doi.org/10.3389/fpsyg.2020.01695