Circadian Sleep/Wake Cycles
Circadian rhythms are present in all living organisms and are also present specifically at the individual cellular level. The most researched area in circadian rhythms is sleep/wake cycles, when we refer to circadian rhythms from here on out we will be referring to sleep/wake cycles.. External stimuli such as meal timing and light exposure seem the most influential on entrainment of the circadian sleep/wake cycle. The most notable however is exposure to light. At the cellular level the circadian cycles are controlled at the suprachiasmatic nucleus (SCN) 4.
Disruption to the circadian cycle or misalignment between internal circadian rhythms with the 24 hour external environment would result in disorders such as poor sleep, metabolism dysfunction, cognitive impairment, cardiovascular abnormalities, gastrointestinal and genitourinary dysfunctions 5.
A misaligned circadian sleep wake cycle is primarily governed by misappropriated light exposure at varying points of the day. Phase shifting occurs when we are exposure to the wrong light or not enough light at typical times of the 24 hour day. For example if we are exposure to artificial light during hours of darkness our sleep cycle will shift forward. The reserve would be true if we expose ourselves to sunlight upon waking, the phase shift will be backward6. “The melanopsin containing retinal ganglion cell is the primary circadian photoreceptor and is most sensitive to blue light”7. During exposure to blue light the SCN advises the pineal gland to cease producing melatonin which makes us feel alert and awake. This is typical from exposure to the sun upon waking and through the lit hours. The opposite is true when we are exposed to no blue light or complete darkness3. Melatonin is secreted and we begin to feel sleepy until we fall asleep.
There are two mechanisms by which human sleep onset is governed. Firstly the homeostatic process which is a drive for sleep which increases during awake hours. Secondly, the circadian driver for sleep which is governed by exposure to light during the day and no light after dark. When one of these mechanisms falls behind the other will “pick up the slack” and compensate for the other. This shows their dependence on each other for system harmony and synchronisation. The importance of this is that they both need to be entrained and in sync with each other in order to optimise sleep/wake cycles.
The issue we have in today’s digital world is that we are surrounded by blue LED lights constantly. Whether it be from digital technology such as smart phones, tablets, laptops or TVs or through exposure to LED lighting inside and outside the abode after dark (street lights, wall lights and car headlights). This blue light is suppressing melatonin and disrupting our circadian cycles. The result is poor sleep and a whole host of metabolic, cognitive and physiological mismatches.
Artificial Blue Light during Dark Hours
Burkhart and Phelps state that “blocking blue light could create a form of physiologic darkness” meaning that in blocking blue light only we can trick the body into thinking we are in complete darkness and begin secreting melatonin optimally and this will create more optimal sleep, recovery and mood1.
In 2009 Burkhart and Phelps1 conducted a randomised control trial (RCT) with the objective of testing amber lens glasses vs. yellow tinted lenses. 20 volunteers were given either amber or yellow lenses to wear 3 hours before bed time. The volunteers completed a sleep diary a week before utilising the glasses and then for 2 weeks whilst wearing the glasses. The amber lens group reported a statistically significant improvement in not just sleep quality and duration but also in their moods.
This is further reinforced by a study released on 14th October, 2017 by Dr.Rabin, Bittner, Van and Mutti where they showed 56% increases in melatonin secretion whilst wearing amber tinted lenses that block blue light when worn before bed2,. Circadian entrainment is directly controlled by short wavelength light through a response from photosensitive retinal ganglion cells. Therefore Van suggests that evening artificial light exposure causes dysregulation of melatonin which is strongly associated with impaired mood and cognitive performnace3.
In the RCT cited above they tested for mood, cognitive performance and sleep onset in 24 students. The group utilised clear lenses for a week followed by amber tinted lenses before sleep, for another week. The amber tinted lenses were designed to block out short wavelength blue light. During the 7 days the subjects wore the amber lenses they had an increase in melatonin levels, less awakening during sleep and evidence of improved cognition. This was in comparison to the week they wore the clear lenses 2,3. When the subjects wore the amber lenses their mean melatonin levels increased from 4.9 pg/mL to 9.6 pg/mL, almost double melatonin production at the appropriate time before bed. Van also notes in the study that "several people who took more than half an hour to fall asleep without the glasses reduced this time to 10 to 20 minutes, on average, when wearing the glasses”.
Blue Light, Sleep and Sports Performance
It has been shown in recent evidence that elite level athletes are most likely to suffer from reduced quality and/or quantity of sleep8. Lack of sleep can lead to suboptimal performance and also lead to issues such as reduced learning ability, memory, cognition, pain perception, immunity and inflammation. The above issues are far from ideal when it comes to conditioning athletes for optimal performance output and must be managed accordingly. Furthermore, given the increased use of nutrition plans in sports science to improve athlete performance, this may have differing effects on subjects across a sports team. This is due to the fact that lack of sleep impairs carbohydrate metabolism thus creating a negative influence on specific macronutrient nutritional plans aimed at improving performance8. If sleep is altering carbohydrate metabolism then sports nutrionists may be working in vain with some athletes and sleep should be addressed first to optimise any nutritional interventions looking to optimise sporting performance.
A good example of this could be the adoption of ketogenic dieting protocols by the Australian National Cricket team for reducing the weight of some of their athletes. Despite its success in reducing the BMIs of some of their cricketers it may have been unnecessary to remove an entire macronutrient if carbohydrate metabolism was analysed in relation to sleep/wake cycles. Lack of sleep and disrupted circadian cycles have also been shown to increase unfavourable changes at the endocrine level. Studies have been released that support this anecdotal suggestion showing the levels of ghrelin (hunger hormone) increases and leptin (satiety hormone) decreases with disruption to sleep/wake cycles11.
No nutrition plan in the world can offset biological cravings for fatty carbohydrate rich foods brought about through endocrine disharmony as a consequence to lack of sleep. This is why lack of sleep and disrupted circadian biology is associated with weight gain and diabetes. Manage sleep and you manage hormones and nutrition as a consequence.
Studies have also looked at endurance performance in association with disrupted sleep. In 2009 Oliver et al. released a study9 showing that after only one night of sleep deprivation, endurance treadmill performance decreased by 8.1%. In relation to soccer where distances in excess of 12km over 90 minutes are common place, this is a worrying statistic given sports science teams are looking to enhance performance output. This would be almost a kilometre less distant travelled during a match based on poor sleep over just one night. Sprint times have also been shown to decrease in athletes with sleep deprivation. A study by Skein et al. reported a significant decrease in sprint times following just 1 day of sleep deprevation10.
We have shown above through recent academic studies that sleep can be managed by blocking artificial blue light in the evenings and exposing ourselves to it during the day. Given many major elite athletes train outside the exposure to day time blue light is not the issue. The issue comes during the hours of darkness. We have also seen that lack of sleep can result is decreased physical, cognitive and metabolic function in elite athletes.
There are two areas to analyse when it comes to performance, light and sleep so the article will take a brief look at both and summarise the solutions in each section. The two potential triggers for reduced sleep and performance we have identified with elite athletes are as follows:
Exposure to artificial light at night before sleep
Circadian disruption brought about by crossed time zones
Blue Light at Night
It has been discussed in this article that artificial blue light at night specially three hours before and leading up to sleep time is suppressing melatonin levels and affecting both sleep quality and duration. Various studies have shown that blocking blue light with amber lens glasses prior to sleep improves sleep quality, cognition and performance. When an athlete finishes their training for the day they will be exposed to the same blue light after dark as the general population. This will include; smart phones, tablets, laptop computers, games consoles, LED televisions, artificial home lighting, street lighting and car headlights. All of these sources of digital technology and lighting emit huge amounts of melatonin suppressing blue light which is the root cause of decreasing sleep quality and quantity.
The below spectrum report shows how much more intense the blue light is from LED lighting found in all digital technology and house lighting, when compared to the moon12.
In order to counteract the amount and intensity of sleep disrupting blue light from digital devises we can either sit in complete darkness or block the melanopic spectrum (more on this later when we discuss our lenses). To block blue light and increase melatonin as the article above suggests, elite athletes need to be wearing amber tinted glasses at least 3 hours prior to bed time.
Another major issue for elite sports teams at a national level is they often have to travel to fixtures across time zones. This is true for national teams but also domestic teams in Australia, given the continent’s huge size.
Jet lag is characterised by symptoms of difficulty falling or staying asleep, day time sleepiness and fatigue5. Zhu and Phyllis in 2012 show that one off short duration travel does not have a huge effect on jet lag but continued travel across time zones on a regular basis intensifies circadian disruption. Given the fixture schedule in major continental or national competition the continued travel to compete in matches will take its toll on the player’s circadian rhythms over the season and maybe permanently season-to-season. We have seen the evidence stack up in relation to circadian disruption and reduced sports performance so we must take steps to reduce this.
It is generally more difficult to adapt to eastward travel, this is not good for sporting sides, who travel to the east is frequently. For eastward travellers symptoms may include difficulty falling asleep, excessive daytime sleepiness and decreased day time performance, most notably in the mornings5. For those travelling west the symptoms will be maintaining sleep, early evening sleepiness and decreased performance. If left unmanaged these types of symptoms may lead to more complex issues such as insomnia or metabolic dysfunction.
In order to treat jet lag we need to realign an individual’s circadian rhythms with the destination location. So travelling to the east we would need to create a phase delay and the opposite to the west. This can be managed through bright light exposure and blocking at various points during the day depending on the context13. So, for eastward travel one should increase bright light in the mornings and reduce it at night. This would work by being outside all morning in the sunlight or if sunlight is not present then artificial sources. However, sunlight would be optimal. It would also mean blocking blue light in the evenings leading up to travel and during travel (if the travel is early evening or at night). This can be achieved by wearing blue light filtering glasses with amber lenses. When flying west one should decrease light exposure in the mornings and increase it during late morning and afternoon, whilst still blocking blue at night. The timings of the above protocol will be influenced by the number of time zones traveled through and duration of time at the destination’s time zone.
Our body’s sleep/wake cycles are primarily stimulated through environmental cues from light. When we rise at first light, light from the sun hits our pineal gland and melatonin is suppressed. The consequences are we feel alert and awake. As the day continues on and the sun begins to set and light disappears our pineal gland will begin to secrete the hormone melatonin making us feel sleepy. Therefore we can conclude that light makes us alert and awake and darkness makes us sleepy. We can take this one step further from the experiments listed above that it’s the blue light frequencies that are the issue so we need to look at management of blue light to optimally regulate sleep/wake cycles.
Whilst travelling through time zones on aircraft we are exposed to artificial light constantly.
In the days leading up to a time zone change it has also been argued that light therapy can help with jet lag. For example, in the days leading up to a flight subjects should block blue light during the dark hours of the destination country or expose themselves it blue light in times of destination country’s day time. Dr Michael Grandner who is the director of the Sleep and Health Research Program at the University of Arizona has studied this is great detail4. However, I believe this would be practical for shorter time differences but in terms of almost complete reversal of day/night in host to destination country coupled with training commitments in elite sporting teams this would not be a practical protocol for a long period of time prior to an important match.
A better method would be to manage the blue light in accordance to the long haul destination whilst on the flight of a day before maximum.
Another important factor to consider is that our eyes do not have to be open for light to pass through the pineal gland and suppress melatonin. In 2016 a study emerged from the Stanford Sleep Epidemiological Research Centre in California. In their study they showed that subjects who were exposed to artificial light during periods of sleep would experience less sleep overall than those who slept in total darkness15. This shows us the darkness whilst sleeping is also an important consideration and one that needs to be addressed in jet lag management. The simple fix would be silk black eye masks. These help block exposure to artificial lights on aircraft during a sleep cycle and also from street lights whilst in the home. Blue blockers on flights are a great help but blocking all light whilst physically asleep also appears important.
At BLUblox we have supplied our glasses to National sporting teams and major league athletes in almost every sport.
When researching which level of tint to use on our lenses we first needed to understand what spectrum of blue light needed to be blocked in order to optimise melatonin production during periods of darkness. Burkhart and Phelps1 classify the visible electromagnetic spectrum needed for circadian regulation being in the blue and some green frequency range. The blue range is defined as wavelengths of light between 380-530 nanometres (nm).
Their RCT was designed to see if subject’s sleep quality improved off the back of wearing either amber or yellow tinted lenses 3 hours prior to sleep.
The results showed that those wearing the amber lenses experienced significantly better sleep than those in the control group1. Amber lenses block blue light across 380-500nm at varying levels depending on the darkness of the tint.
What we concluded from these results was that the range of light we need to focus on blocking is approximately between 380-530nm in relation to the above spectrum chart. Anymore blockage would impair vision and reduce the likelihood for athlete wearing the glasses. Given the trial showed a significant improvement in sleep quality we concluded that any addition spectral blocking would not be warranted given the issues of distortion and headaches reported with blue blockers that block 99-100% of light from 380-570nm. This is further backed up from a study released on 14th October, 2017 by Dr.Rabin, Bittner and Mutti where they showed 56% increases in melatonin secretion whilst wearing amber tinted lenses that block light only between 380-530nm2,3.
It is important to optimise melatonin secretion to a point where both sleep is improved and quality of vision and life is maintained.
From Burkhart and Phelps’ RCT we can also firmly state that amber lenses are far superior to yellow lenses for managing circadian cycles. Yellow tinted lenses in the context of blue light management are typically utilised during the day time hours where subjects are exposed to excess artificial blue light from digital devises. They are not optimal for use past sunset as they simply do not block enough light across the blue spectrum. When your look at companies that produce lighter tints or gaming glasses they focus their marketing on digital eye strain and only briefly touch on sleep. Also, from analysing their websites and lens reports they block anywhere between 10-50% of blue light. It also appears that the primary function of paler tinted lenses is to reduce digital eye strain2, which is a problem in itself, but does not address the issues of pre-bed melatonin impairment from exposure to blue light.
BLUblox lenses (see below) block 98% of blue light from 380-500nm and 90% of green light. This allows for peak melatonin secretion when worn prior to a sleep cycle whilst not impairing vision or blocking too much other light colours that leads to reported headaches, distorted vision and dizziness.
American Academy of Optometry (AAOpt) Annual Conference. Presented October 12, 2017.
Storch KF, Lipam O, Leykin, et al. Extensive and divergent circadian gene expression in liver and heart. Nature. 2002;417:78-83
Lirong Zhu, MD, PhD and Phyllis C. Zee, MD, PhD. Circadian Rhythm Sleep Disorders, Neurol Clin. 2012;1167-1191:2
Czeisler CA, Allan JS, Strogatz SH, et al. Bright light resets the human circadian pacemaker independent of the timing of the sleep-wake cycle. Science. 1986;223”667-671
Ruby NF, Brennan TJ, Xie X et al. Role of melanopsin in circadian responses to light. Science. 2002;298:2211
Shona L. Halson. Sleep in elite athletes and nutritional interventions to enhance sleep Sports Med. 2014;44(suppl 1)13-23
Oliver SJ, Costa RJ, Laing SJ, et al. One night of sleep deprivation decreases treadmill endurance performance. Eur J Appl Physiol. 2009;107(2)
Skein M, Duffield R, Edge J et al. Intermittent-sprint performance and muscle glycogen after 30 hours of sleep deprivation. Med Sci SportsExerc. 2011;43(7)
Shahrad Taheri, Ling Lin, Diane Austin, Terry Young, Emmanuel Mignot, Short Sleep Duration Is Associated with Reduced Leptin, Elevated Ghrelin, and Increased Body Mass Index. 2004
Boulos Z, Campbell SS, Lewy AJ, Terman M, Dijk DJ, Eastman CI. Light treatment for sleep disorders: consensus report. VII. Jet lag. Journal of biological rhthyms. 1995