Which road bike is the best? An Italian classic like the Pinarello Dogma or a high-performance machine a la Specialized Tarmac? This is a matter of great debate among road cyclists. However, all cyclists probably agree on one thing: everyone wants to sleep a lot and well. But what is the best way to achieve restful sleep? What role does nutrition play and why should we think about wearing sunglasses while cycling? These questions will be clarified below.
Without adequate sleep, the best training is for the ton. Sleep ensures recovery from strenuous exercise and keeps us healthy. But when is sleep optimal? For optimal sleep, the individually necessary duration of sleep must be achieved and the processes that take place during sleep must take place comprehensively. Duration and quality are thus the two supporting pillars of our sleep. What is the necessary sleep duration? The necessary sleep duration varies from individual to individual and also depends on the individual himself and his respective life circumstances. Neuroscientist and sleep researcher Matthew Walker points out that most people in Western industrialized nations underestimate their need for sleep and chronically sleep too little. He advocates at least eight hours of sleep a day. For athletes, the daily requirement is higher, as the level of recovery is increased by exercise. In fact, many professional athletes report that they would sleep at least nine – if not ten or more – hours a day. According to sleep researcher Walker, it is also possible to achieve the necessary hours of sleep by combining nighttime sleep with a short midday or afternoon nap. However, sleep during the day is less “high quality” in terms of quality, so catching up on sleep during the day has its limits. Scientists in sleep research are faced with a challenge: How can people be helped to increase their sleep quality? After all, if you don’t get enough (good) sleep, you’re very likely to get sick in the long run. The list of consequences of insufficient sleep is long: obesity, cardiovascular disease, depression, diabetes, acceleration of aging processes, dementia and much more.
Chronobiology explains why we do not get extensive, restful sleep during the day. Chronobiology is a branch of biology that involves the study of temporal regularities in the course of life processes. It speaks of a circadian rhythm, a sleep-wake rhythm or biological rhythm, which is found in plants, animals and humans. This rhythmicity occurs, for example, in periodic changes in heart rate, blood pressure, or body temperature. Our hormones such as insulin, the stress hormone cortisol or growth hormones are subject to the sleep-wake rhythm. Our immune system, our digestion as well as energy supply, our cognitive performance and many other metabolic functions are influenced by the internal clock. In view of this, one can imagine what a disturbance of the sleep-wake rhythm does to our body and psyche.
Daylight acts as a clock for the sleep-wake rhythm. Daylight enters our eyes and hits the retina, creating nerve impulses that serve as signals to our brain and trigger certain metabolic processes. This synchronizes our body cells like the conductor synchronizes the musicians in an orchestra. But not all light is the same. A certain light intensity is necessary for the stimulus to synchronize the sleep-wake rhythm, which is not achieved by our usual indoor lighting, but happens with bright daylight. The luminous intensity of sunlight varies depending on the season, weather and location on earth. Lack of or insufficient bright daylight is associated with disturbed sleep-wake rhythm and numerous diseases. To prevent this, so-called light therapy is sometimes used when there is a lack of daylight. In light therapy, patients are exposed to bright light for a certain period of time, whereby short to medium wavelengths in the visible range are used here for the therapeutic effect. This mainly affects people in countries north of the Arctic Circle, such as parts of Norway or Sweden. Here, the sun is often not visible for months. Even here in Germany, light therapy is helpful during the winter months. Many people arrive at work in the morning before it gets light and return home in the evening after sunset without having seen daylight. Thus, our body does not receive sufficient stimulus to clock the sleep-wake rhythm. In contrast, bright light after dusk is counterproductive for a restful night. The unnatural brightness that we generate through artificial indoor lighting and not least with technical devices such as smartphones, televisions or PCs upset our internal clock. The shorter-wave blue light in particular was previously blamed for disturbing sleep. More recent studies suggest that blue light does have an effect, but that the influence of the absolute brightness of the light falling on the eye is significantly greater. The brightness of artificial ambient light and the screen brightness of electronic devices should therefore be significantly reduced in the evening.
Cooling down the body is also important for a good night’s sleep with sufficient regeneration. Our core body temperature has a diurnal cycle. It drops at the beginning of the night’s rest until the early morning. In the morning, the core body temperature rises again to a “normal” level. Our brain also cools down at night. This reduction in temperature is crucial for regenerative processes in the body. Bedroom temperatures of over 18 degrees should be avoided at all costs. In the wild, such comparatively high temperatures in Central Europe occur only on a few hot tropical nights. In order to help the body to cool down, one must give it the feeling that acutely no cold phase or deepest winter prevails. In evolutionary terms, this could mean death by freezing to death during sleep, which is why the body hesitates to lower its temperature. That is why it is difficult to fall asleep with cold feet. Here it helps to warm cold feet and generally increase the skin surface temperature e.g. by a warm shower or a bath.
In addition to the circadian rhythm in our cells, a second component serves as a boundary condition for the sleep-wake rhythm: sleep-wake homeostasis. What sounds complicated is basically simple and familiar to all of us: The less we sleep, the greater the need to sleep. The so-called “sleep pressure”, i.e. the perceived pressure to sleep, increases the longer we are awake and the worse we have slept. This sleep pressure explains why we are dog-tired and fall asleep even on a bright summer day after an all-nighter in the proverbial broad daylight. This sleep pressure is caused by an increase in adenosine in the brain, which is broken down during sleep. Adenosine is the “fatigue maker” that is created when we exert ourselves and burn energy. The universal energy carrier ATP AdenosineTriPhosphate contains adenosine and when it is utilized, adenosine residues remain and accumulate in the brain. Adenosine docks with special receptors in the brain and thus makes us tired. Lack of exercise is one cause of the increasing sleep disorders in our society. People who are less active need less energy and thus less of the energy carrier ATP. Less adenosine is produced and sleep pressure is reduced. An evening walk or bike ride in the evening can work wonders. In general, cycling promotes a good night’s sleep through exertion. By the way, this is also the reason for the wake-up effect of caffeine. Caffeine attaches itself to the adenosine receptors and blocks them for adenosine. Therefore, caffeine makes you awake. The half-life of caffeine breakdown in the body – the time it takes for half of the caffeine to be broken down – varies between 1.5 and 9.5 hours. At larger doses, the breakdown tends to be slower. Caffeine may well be present in the body for 24 hours and thus disturb sleep. Anyone who suffers from problems falling asleep or sleeping through the night should therefore avoid large amounts of caffeine and taking it in the hours before bedtime.
In recent years, melatonin has become known as a sleep aid. The intake of melatonin should help to a restful sleep. What is melatonin? Melatonin is a hormone that is released by our brain as soon as dusk sets in and daylight disappears. Bright daylight falling into our eyes tells our brain that it is daytime. As soon as this signal is lost due to the lack of light, the so-called pineal gland – an organ in our brain – starts producing melatonin. Melatonin is important for the quality of sleep. With the release of melatonin due to the onset of darkness, the metabolism adjusts to the upcoming sleep. Contrary to what one might expect, the melatonin level is not at its highest at the beginning of the night’s rest, but continues to rise until the early morning. The peak of the melatonin level is around three to four o’clock in the morning. After that, the melatonin concentration drops again, without us already being exposed to sunlight. At this point, the “master player” comes into play, one of our body’s most powerful hormones: the stress hormone cortisol. Cortisol has a natural diurnal cycle in the body with the highest concentration in the early morning. Cortisol sets the stage for waking up. In the evening at bedtime, cortisol drops to a minimum. Excessive cortisol levels in the evening and during the first half of the night are a common cause of difficulty falling asleep and staying asleep. Therefore, no more very strenuous sports should be done in the late evening, during which cortisol is released. In addition, all stress and excitement should be avoided. The high cortisol in the early morning sends the signal that the day is dawning and ensures that melatonin is broken down again. Daylight ensures that melatonin levels remain low. In winter, very little or no daylight often reaches our eyes. Melatonin levels then often remain chronically elevated and the fluctuations in melatonin levels during the day are smaller. We feel tired during the day and yet sleep poorly at night. An increased melatonin level can often be measured in depressed people. In winter, many people suffer from so-called winter depression as a result. Especially in winter, sunglasses with a high darkening factor are therefore counterproductive when cycling. Although taking melatonin can increase the fluctuations in melatonin levels, our melatonin concentrations are already elevated in winter due to a lack of light. Taking melatonin has positive effects in certain diseases. For example, in type 2 diabetes, melatonin increases insulin sensitivity, which means less insulin needs to be injected at mealtimes. However, this effect can also be achieved with exercise, and more sustainably. Taking melatonin also has side effects. When taking melatonin, sedation the next day and an increase in vivid dreams or nightmares are often observed. Critics such as scientist Patrick Fuller point to a possible placebo effect. In diseases such as dementia, the use of melatonin preparations may be considered, although even here light therapy or daylight showed a greater effect than melatonin alone and also improved mood. In clinically healthy people, melatonin should rather be avoided. Not all interactions have been researched yet.
Our diet can support sleep. On the one hand, WHAT we eat has an influence on sleep, especially dinner. If we eat food that is difficult to digest, this can severely disturb falling asleep and sleeping through the night, since the gastrointestinal tract is also subject to circadian rhythms. In addition, the digestion of food generates heat. Protein-rich foods in particular release heat during digestion. Although this high thermogenesis is desirable, e.g. for weight reduction, it hinders the body in its cooling down of the core temperature. Protein-rich foods should therefore not necessarily be consumed as bedtime snacks. However, a serving of protein with dinner can promote sleep. Especially foods rich in the amino acid tryptophan. The hormone melatonin is formed from the “happiness hormone” serotonin. Serotonin in turn requires the amino acid tryptophan for its production in the brain. However, tryptophan cannot simply reach the brain, as it has to cross the natural protective barrier known as the blood-brain barrier. The brain only allows a certain amount of amino acids through this barrier at any given time, so tryptophan always has to compete with other amino acids. This is where the hormone insulin can be helpful. Insulin channels a large part of the other amino acids for regeneration, e.g. into the muscles, so that the path for the tryptophan into the brain is cleared. People who cycle and do sports have a better insulin sensitivity of the muscles, which increases this effect. Tryptophan is now being used to help people fall asleep and stay asleep. A classic for falling asleep is warm milk with honey. Scientific proof of this sleep aid is difficult. Whether it is merely a placebo effect, whether the influence of the warmth of the drink leads to relaxation or whether a role is played is difficult to prove exactly. One explanation why warm milk with honey helps to fall asleep is the fact that milk contains tryptophan and the sugar in honey raises insulin levels. According to scientific research, sugary foods and drinks help shorten the time it takes to fall asleep if they are eaten several hours apart from bedtime. Insulin causes the level of the stress hormone cortisol to decrease, which is important for falling asleep and the first stages of sleep at the beginning of the night’s rest. However, too much sugar consumption should be avoided just before bedtime, as blood sugar fluctuations can occur during sleep and affect hormones such as leptin and gherlin. So not only WHAT we eat, but above all the timing, i.e. WHEN we eat, tackles our sleep-wake rhythm and promotes or reduces the quality of sleep. Here, there can be great individual differences in when the last meal of the day should take place. Only the right individual combination of WHAT and WHEN brings the solution.
Last but not least, it is important for healthy sleep to accept and support the circadian rhythm. Artificial light, sunglasses and hormones can influence our sleep-wake rhythm. However, it is difficult to completely eliminate all factors, especially since they are not yet fully known even to researchers. During sleep, different sleep phases alternate. In the first half of the night, the deep sleep phase dominates, while in the second half of the night, the proportion of dream sleep, also called REM (rapid eye movement) sleep, increases. The individual phases have their function. If the individual phases and their function are insufficiently achieved in one night, the special sleep can be conditionally made up for in the following nights. By ringing the alarm clock too early, we often miss part of REM sleep and, conversely, by going to bed too late, we miss sufficient deep sleep. The reason for the latter is the natural sleep-wake rhythm and associated processes. Just because we go to bed later does not mean that hormones such as cortisol are released later. We can’t outsmart our internal clock by staying in bed longer. To be in tune with our natural internal clock, we need to respect the times of dawn and dusk. This is where the expression “midnight” comes from. Midnight is temporally between dawn and dusk. When we turn night into day with artificial light in the evening and regularly go to bed just before midnight, we chronically miss out on some of our deep sleep. According to sleep researcher Walker, a lack of deep sleep can lead to dementia. That’s because deep sleep is the only time the brain is cleansed of waste products.
In a study from 2012, factors influencing a shift in the sleep-wake rhythm of shift workers were investigated. The aim was to turn day into night and vice versa. The greatest influence on the shift from day to night was achieved by bright artificial light, to which shift workers were exposed at night. Here the shift was so great that wearing dark sunglasses (transmission 2 percent) during the day and taking melatonin could not increase the magnitude of the shift. In the case of room light only during the night shift, sunglasses with high darkening supported the shift. The effect was greatest with the more darkening glasses. Taking melatonin did not further increase the shift when sunglasses were already in use. So wearing dark sunglasses while cycling, does have an effect on our sleep-wake cycle. As mentioned, this affects melatonin levels. Especially in winter, wearing dark sunglasses should rather be avoided. Those who commute to work by bicycle sometimes prolong the depletion of melatonin in the early morning by wearing dark sunglasses. Wearing them in the late afternoon and evening can be helpful for falling asleep and staying asleep. However, in this case, as well as in general, bright, artificial ambient light should be avoided in the hours before bedtime.
Tips for a healthy sleep:
- Bedroom temperature at a maximum of 18 degrees
- Avoid cold feet and warm up before going to bed.
- Avoid artificial light in the evening or reduce brightness if necessary
- Exercise during the day
- Do not exert yourself physically or mentally in the evening
- Avoid stress
- Do not eat too late in the evening
- Do not eat hard-to-digest and protein-rich foods shortly before bedtime
- Eat carbohydrates a few hours before sleeping, but avoid large insulin spikes
- Stay outside during the day and preferably in the morning in bright daylight, alternatively use daylight lamps
- Avoid dark sunglasses on dark winter days
- Do not go to bed too late, midnight should be close to the middle of the night’s rest
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Further reading:
Ahmad Afaghi, Helen O’Connor, Chin Moi Chow, High-glycemic-index carbohydrate meals shorten sleep onset, The American Journal of Clinical Nutrition, Volume 85, Issue 2, February 2007, Pages 426–430, https://doi.org/10.1093/ajcn/85.2.426
Crowley SJ, Lee C, Tseng CY, Fogg LF, Eastman CI. Combinations of bright light, scheduled dark, sunglasses, and melatonin to facilitate circadian entrainment to night shift work. J Biol Rhythms. 2003 Dec;18(6):513-23. doi: 10.1177/0748730403258422. PMID: 14667152.
Atul Khullar, MD, MSc, The Role of Melatonin in the Circadian Rhythm Sleep-Wake Cycle July 10, 2012 Psychiatric Times, Psychiatric Times Vol 29 No 7, Volume 29, Issue 7
Owczarek G, Gralewicz G, Wolska A, Skuza N, Jurowski P. Potencjalny wpływ barwy filtrów w okularach chroniących przed olśnieniem słonecznym na wydzielanie melatoniny [Potential impact of colors of filters used in sunglasses on the melatonin suppression process]. Med Pr. 2017 Jul 26;68(5):629-637. Polish. doi: 10.13075/mp.5893.00550. Epub 2017 Jul 10. PMID: 28731071.
Deacon S, English J, Arendt J. Acute phase-shifting effects of melatonin associated with suppression of core body temperature in humans. Neurosci Lett. 1994 Aug 29;178(1):32-4. doi: 10.1016/0304-3940(94)90282-8. PMID: 7816333.
Cipolla-Neto, J., Amaral, F.G., Afeche, S.C., Tan, D.X. and Reiter, R.J. (2014), Melatonin, energy metabolism, and obesity: a review. J. Pineal Res., 56: 371-381. https://doi.org/10.1111/jpi.12137
Bass J, Lazar MA. Circadian time signatures of fitness and disease. Science. 2016 Nov 25;354(6315):994-999. doi: 10.1126/science.aah4965. PMID: 27885004.
Walker PhD, Matthew. Why We Sleep: Unlocking the Power of Sleep and Dreams. ISBN: 9781501144318
Skene DJ, Deacon S, Arendt J. Use of melatonin in circadian rhythm disorders and following phase shifts. Acta Neurobiol Exp (Wars). 1996;56(1):359-62. PMID: 8787196.
Esaki Y, Kitajima T, Takeuchi I, Tsuboi S, Furukawa O, Moriwaki M, Fujita K, Iwata N. Effect of blue-blocking glasses in major depressive disorder with sleep onset insomnia: A randomized, double-blind, placebo-controlled study. Chronobiol Int. 2017;34(6):753-761. doi: 10.1080/07420528.2017.1318893. Epub 2017 May 10. PMID: 28488943.
Tähkämö L, Partonen T, Pesonen AK. Systematic review of light exposure impact on human circadian rhythm. Chronobiol Int. 2019 Feb;36(2):151-170. doi: 10.1080/07420528.2018.1527773. Epub 2018 Oct 12. PMID: 30311830.
Harding, Edward C et al. “The Temperature Dependence of Sleep.” Frontiers in neuroscience vol. 13 336. 24 Apr. 2019, doi:10.3389/fnins.2019.00336
Schneider-Helmert D, Spinweber CL. Evaluation of L-tryptophan for treatment of insomnia: a review. Psychopharmacology (Berl). 1986;89(1):1-7. doi: 10.1007/BF00175180. PMID: 3090582.
Riemersma-van der Lek RF, et al.: Effect of bright light and melatonin on cognitive and noncognitive function in elderly residents of group care facilities. A randomized controlled trial. JAMA 2008; 299: 2642–2655.
Howard RJ, et al.: Donepezil for the treatment of agitation in Alzheimers disease. N Engl J Med 2007; 357: 1282–1392.
Institute of Medicine (US) Committee on Military Nutrition Research. Caffeine for the Sustainment of Mental Task Performance: Formulations for Military Operations. Washington (DC): National Academies Press (US); 2001. 2, Pharmacology of Caffeine. Available from: https://www.ncbi.nlm.nih.gov/books/NBK223808/
Porter JM, Horne JA. Bed-time food supplements and sleep: effects of different carbohydrate levels. Electroencephalogr Clin Neurophysiol. 1981 Apr;51(4):426-33. doi: 10.1016/0013-4694(81)90106-1. PMID: 6164541.
