The Circadian Rhythm — A Thorough Review For Better Sleep and More Productivity
A guide to excellent sleep and superb alertness during the day
These (1, 2) articles explored how sleep is greatly influenced by the inner workings in our body, most importantly our hormones, as well as the outer workings of the world, most importantly light and darkness.
To bring both of these together and combine them in one holistic principle, this article will explore the circadian rhythm. Note that you do not have to read the other articles to understand this one, but we recommend to do so to make full use of it.
Circadian rhythm sounds sophisticated itself, but is — once dissected — very simple and the single most helpful tool to understand how to sleep healthier. Often, we call it our body clock or biological clock. Fathoming and practically using this concept has fundamental implications on your overall health, longevity and productivity. If our circadian rhythm is in sink, so are our hormone cycles. We feel alert during the day, have a better mood and fall asleep easily.
Our circadian rhythm is the product of millions of years of evolution and was almost exclusively unimpaired in the past. Yet, in today’s world ruled by work related stress, constant disturbance and artificial light, it is shaken up and disrupted in many of us. Fixing this perilous phenomenon is one of the key rules for healthy sleep and productivity.
There are two interesting implications of understanding our circadian rhythm.
Firstly, we can use our understanding of it to reactivate it — i.e. cure it in case it was impaired. All we need to do is to control external stimuli affecting our body.
Secondly, once it is in sink, we can use knowledge about healthy circadian rhythms to optimize the timing of our daily activities.
1. Getting your circadian rhythm in sink
First of all, you should look at indicators as to whether your circadian rhythm is in sink or not.
- Do you have trouble falling asleep or getting up in the morning?
- Do you get very tired in the afternoon?
- Do you experience sudden productivity rushes during the late evening / night?
- Do you have disturbed sleep?
- Is your stool and are your hunger cravings inconsistent?
If you answered yes to any of these questions, there is eligible apprehension that your circadian rhythm might not be in sink. This is definitely not the end of the world. It’s veritably great news: There is room for optimization. Fortunately, science has to say a whole lot about our circadian rhythm and there are fantastic ways of ‘manipulating’ our hormones to get it back on track. The most straight forward rules are:
A. Routinize your life
Step 1: Stand up at the same time, always. Go to bed at the same time, too, if possible. Consistency is very important and highly increases sleep quality . If you go to bed later or earlier than expected, your hormones will not have adjusted quick enough. Going to bed too early leads to melatonin not yet being secreted and your sleep quality suffering as a consequence. Going to bed too late may result in growth hormone release being deferred and cortisol kicking in too early.  There are certain hormones that help us sleep and certain hormones that help us be awake. Confusing our body unnecessarily much by staying awake when our body wants us to sleep and the other way round is not helpful. As complicated as this sounds, it can be summarized in one easy lesson: More regularity in your daily schedule translates into better sleep and feeling more alert.
Therefore, step 2: Eat meals at the very same time throughout the week. Especially regularity in the timing of evening meals is associated with better sleep onset.  Meals provide you with energy and hence trigger physiological effects. The more you stick to a schedule, the better your sleep becomes. Moreover, many of your organs have internal ‘clocks’ that adjust to your rhythm. Your liver clock may re-adjust in three days, but your heart clock, for instance, needs a longer period of up to seven days.  By adding irregularity to your day, especially when it comes to sleep and eating, all you do is confusing your organs. Don’t do that if you want to feel more alert and sleep better.
Step 3, for the very disciplined: If possible, stick to a rhythm as rigid as possible concerning all of your daily activities. Studies show that people who leave their house at approximately the same time every day do have healthier sleep . Moreover, starting work at the same time was also associated with healthier sleep. Just as interestingly, this holds only true for younger adults, while older adults (60+) benefited from greater variability in their daily activities .
Note that there are psychological effects, i.e. those affecting your mind, feelings and thoughts, and physiological effects, i.e. those affecting your inner body and biology. Firstly, psychological effects associated with more regularity are usually negative, including increased boredom, burn-out and inability to adapt to external changes . This makes intuitive sense: It can be very boring and unexciting to do the same things day after day after day. A healthy mixture is always important. Nothing is worse than you not wanting to start into the day. Secondly, physiological effects associated with more regularity are usually positive, including better functioning of your body, better health in general  and less depression . The physiological effects do usually outweigh the negative psychological ones, yet we recommend: Know thyself. Pay attention to your peculiar specifics and individuality. If you get bored quickly and need excitement, try to eat and sleep at the same time, but make sure that the rest of your day stays exciting and unpredictable. If you love routines and structure, there might be fundamental gains, such as needing less sleep to feel alert, to adding more structure to your day. 
B. Use external ‘tools’ to foster hormonal harmony
Drinking coffee in the morning, approximately one hour after being awake, can be a great means to get you going. As discussed in this article, there is usually nothing to worry about when drinking coffee in the morning. Yet, don’t do so if you’re experiencing a lot of stress and pressure — coffee stresses your adrenal glands. 
Using smart lighting techniques, mostly discussed in this article, can furthermore support the regularity from above. Have it very bright in the morning, open all windows and switch on all lights. If there are not enough sources of natural sun light, get a daylight lamp. Light is one of the greatest regulators helping you to sync your circadian rhythm. Also, have it very dark in the evening, start dimming lights and reducing exposure to light up to two hours before going to bed. Make use of apps such as f.lux when using your lap-top at night. 
Have an evening ritual for stress reduction. The hour before going to bed should be spent on leisure and calming down. Do this every single night to condition your body to fall asleep after this ritual.  If you’re really struggling, consider supplements. If your struggling to get up in the morning and often feel you are in a bad mood, you may take 4000 IU of vitamin D3 in the morning, for a week. Also, consider supplementing natural magnesium or GABA in the evening to relieve physical and psychological stress.
2. Leverage your circadian rhythm for ever more productivity
Look at the graph below to see how our circadian rhythm works. Yes, there are times when our coordination is best, our reaction time fastest and our cardiovascular efficiency greatest. These are general patterns rather than immutable truths. Especially when your circadian rhythm is not in sink, you might not resonate with the image below. When you stick to our principles, however, there is a lot we can infer from the picture below.
Do your work-outs between 3 to 5 pm when your cardiovascular efficiency and muscle strength peak. Studies show that working out at that time results in better sleep and yields higher performance.  Do not work out later as the released testosterone and adrenaline as a corollary might suppress your melatonin secretion. 
Track when your alertness is highest. If your circadian rhythm is healthy, it is most likely going to be three to four hours after you got up. This should be the time you do your most challenging tasks, such as working on a project that requires your greatest attention or memorizing if you are at university. The correct timing can boost your productivity greatly; you might be up to twice as productive.
Help warming your body up in the evening, for instance with a cup of tea and help cooling it down during night, f.i. by sleeping without thick clothes. Many studies indicate that you should have it rather cold (16–18 degrees Celsius if you sleep with a sheet) for your body to cool down during night to recover more quickly. 
If you want to have a healthy sleep and master productivity, pay attention to your circadian rhythm daily. Track when you eat, when you start working and when go out of the house. Then, try to add regularity to help your body regulate its inner hormone cycles.
As always, we want to summarize the key rules from this article.
- Add as much regularity to your day as possible, especially by eating and sleeping at the same time
- Have it bright in the morning and dark in the evening
- Warm your body warm up in the evening, for instance by drinking a cup of tea, and cool it down during night.
- If you do a work-out, do it between 3 to 5 pm
The effects of these simple changes can be enormous. In our opinion, paying attention to your circadian rhythm is the simplest and at the same time most effective principle to improve quality of life. Yet, however simple this concept is, most people violate it within the chaos of their hectic life. This leads to more stress, which leads to more chaos, which leads to more stress, and so on and so forth. We encourage you to put an end to this vicious cycle. In most cases, simply realizing that it exists and witnessing its benefits first hand is enough. If not, feel free to comment below — we’re here to help.
Note that this is article one in a whole series of articles. You can find the subsequent articles on our website. After you have read our articles, not only will you have a thorough understanding of your body and your inner workings, but also will you be able to put that knowledge into use and apply it flexibly throughout your live to design your individual desired plan of winning life.
 Onen, S.H., Onen F., Bailly, D., & Parquet, P. (1994). Prevention and treatment of sleep disorders through regulation of sleeping habits. Presse Medicale, 23(10), 485–489. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/8022726?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DefaultReportPanel.Pubmed_RVDocSum
 Bootzin, R. R. (1972). A stimulus control treatment for insomnia. Proceedings of the 80th Annual Convention of the American Psychological Association, 395–396. doi:10.1037/e465522008–198
 Spielman, A. J., Saskin, P., & Thorpy, M. J. (1987). Treatment of chronic insomnia by restriction of time in bed. Sleep, 10(1), 45–56.
 Wu, T., Ni, Y., Zhuge, F., & Fu, Z. (n.d.). Resetting process of peripheral circadian gene expression after the combined reversal of feeding schedule and light/dark cycle via a 24-h light period transition in rats, 27.
 Baron, K. G., Reid, K. J., Kern, A. S., & Zee, P. C. (2011). Role of sleep timing in caloric intake and BMI. Obesity, 19(7), 1374–1381.
 Monk, T. H., Petrie, S. R., Hayes, A. J., & Kupfer, D. J. (1994). Regularity of daily life in relation to personality, age, gender, sleep quality and circadian rhythms. Journal of Sleep Research, 3, 196–205. doi:10.1111/j.1365–2869.1994.tb00132.x
 Monk, T. H., Reynolds III, C. F., Buysse, D. J., DeGrazia, J. M., & Kupfer, D. J. (2003). The relationship between lifestyle regularity and subjective sleep quality. Chronobiology international, 20(1), 97–107.
 Dautovich, N., Shoji, K., & McCrae, C. (2015). Variety is the Spice of Life: A Microlongitudinal Study Examining Age Differences in Intraindividual Variability in Daily Activities in Relation to Sleep Outcomes, The Journals of Gerontology: Series B, 70(4), 581–590. https://doi.org/10.1093/geronb/gbt120
 Zisberg, A., Young, H. M., Schepp, K., & Zysberg, L. (2007). A concept analysis of routine: relevance to nursing. Journal of advanced nursing, 57(4), 442–453.
 Bond, M. J., & Feather, N. T. (1988). Some correlates of structure and purpose in the use of time. Journal of Personality and Social Psychology, 55(2), 321.
 Clark, F., Azen, S. P., Carlson, M., Mandel, D., LaBree, L., Hay, J., & Lipson, L. (2001). Embedding health-promoting changes into the daily lives of independent-living older adults: long-term follow-up of occupational therapy intervention. The Journals of Gerontology Series B: Psychological Sciences and Social Sciences, 56(1), 60-63.
 Brown, L. F., Reynolds III, C. F., Monk, T. H., Prigerson, H. G., Dew, M. A., Houck, P. R., & Kupfer, D. J. (1996). Social rhythm stability following late-life spousal bereavement: associations with depression and sleep impairment. Psychiatry research, 62(2), 161–169.
 Goodman, L., & Gilman, A. (1975). The Pharmacological Basis of Therapeutics. New York: Macmillan.
 Bolton, S., Feldman, M., & Revici, E. (n.d.). A Pilot Study of Some Physiological and Psychological Effects of Caffeine. JOURNAL OF ORTHOMOLECULAR PSYCHIATRY, 13(1), 8.
 Touitou, Y., Reinberg, A., & Touitou, D. (2017). Association between light at night, melatonin secretion, sleep deprivation, and the internal clock: Health impacts and mechanisms of circadian disruption. Life Sciences. 173, 94–206. 10.1016/j.lfs.2017.02.008.
 Rhee, H., Vries, E., Coomans, C., Velde, P., & Coebergh, J. (2016). Sunlight: For Better or For Worse? A Review of Positive and Negative Effects of Sun Exposure. Cancer Research Frontiers, 2, 156–183. 10.17980/2016.156.
 Tayebisani, S., Fooladi, P., Alikhani, F., Aghayan, S., & Zani, H. G. (2012). The effect of weight Training in morning and evening on testosterone and cortisol in. European Journal of Experimental Biology, 2(4), 1109–1112. Retrieved from http://www.imedpub.com/articles/the-effect-of-weight-training-in-morning-and-evening-on-testosterone-andcortisol-in-bodybuilders.pdf
 Vingren, J., Kraemer, W., Ratamess, N., Anderson, J., Volek, J., & Maresh, C. (2010). Testosterone Physiology in Resistance Exercise and Training. Sports, 40(12), 1037–1053. doi: 10.2165/11536910–000000000–00000.
 Bekö, G., Lund, T., Nors, F., Toftum, J., & Clausen, G. (2010). Ventilation rates in the bedrooms of 500 Danish children, Build. Environ., 45, 2289–2295.
 Gilbert, S.S., van den Heuvel, C.J., Ferguson, S.A., & Dawson, D. (2004). Thermoregulation as a sleep signalling system. Sleep Med Rev, 8, 81–93. doi: 10.1016/S1087–0792(03)00023–6.