Sleep is by far one of the most underappreciated necessities to our daily functioning. When it comes to athletes or physically active individuals, it is convincingly the key factor between progressing forward or stalling with:
Learning new motor patterns
Immune system functioning
...just to name a few!
Learning new motor patterns is a part of training. Whether it is learning a complex movement like an Olympic lift, or making minor tweaks to your batting stance or your overhead serve, the general notion behind training is that you perform countless reps of this motor pattern until you build the 'muscle memory' allowing for the movement itself to occur without conscientious effort. However, it's proposed that it is NOT the actual reps being performed during training that imprints this muscle memory, but rather the repetitive processing of this pattern in the brain during sleep (which is possibly then stored into long-term memory) that allows for the eventual adaptations. (Tamaki, et al. 2013)
Cognitive skills can include processing new information but also includes memory, emotional control, hand-eye coordination, and decision-making, to name a few. We have all undoubtedly had those days where nothing seems to work right (uncoordinated, no strength, no patience or just generally moody, and no motivation) and this could largely be attributed to less than optimal sleep efficiency. Even worse: study findings suggest that athletes are more likely to have less than optimal sleep efficiency (meaning poorer quality and quantity of sleep compared to the general population) largely due to the unique combination of increased stress or anxiety from competition, travel demands, caffeine use, various training times, and muscle soreness. (Halson and Juliff, 2017)
Tissue growth and fuel replenishment during sleep occur through several mechanisms, but one of the most notable is the natural increase in growth hormone during nocturnal sleep. (Ritsche, et al. 2014) Growth hormone, as the name implies, promotes tissue synthesis (like muscle and cartilage) and fuel replenishment (like building glycogen stores) by stimulating the release of IGF-1 (which enhances uptake of glucose and amino acids). (Ritsche, et al. 2014) Now growth hormone is largely released in pulses during sleep, but is also released acutely post-exercise to aid in this nutrient uptake. Interestingly, acute sleep deprivation (going 24 hours without sleep) significantly lowered that post-exercise growth hormone release (i.e. a diminished ability to absorb and utilize that post-workout nutrition simply due to lack of sleep the night before). (Ritsche, et al. 2014)
Immune system functioning is also closely related to sleep where study findings have shown that sleep deprivation increases susceptibility for various infectious diseases (i.e. not getting enough sleep now puts you at a greater risk for getting, and staying, sick). (Asif, et al. 2017) Athletes are under increased amounts of stress, both physical and psychological, which in turn taxes their immune system leaving them already MORE vulnerable to infectious agents compared to non-athletes. Add to this a lack of sleep due to those competition or training demands and now there is an even greater risk for undue health effects like the all-too-common upper respiratory infections for example.
So now we have a glimpse at just how important sleep is, but let's take a look at what sleep actually consists of...
Sleep can be divided into stages consisting of:
Rapid eye movement (REM)
Non-rapid eye movement (non-REM) which has 4 stages:
Stages 1 & 2 are considered 'light sleep'
Stages 3 & 4 are considered 'deep sleep'
A typical sleep cycle will look like this:
Often lasting ~90 minutes
First falling into the 'light sleep' of non-REM stages 1 and 2
During light sleep you can easily be woken up, and where brain waves initially increase and then slow down.
Then falling into 'deep sleep' of Non-REM stages 3 and 4
During deep sleep it is difficult to be woken up, and where the brain slows down even more and the body no longer responds to outside stimuli.
During deep sleep the body goes through it's major restorative functions like restoring tissues/muscles, stimulating growth and development, boosting the immune system functions, and building and storing energy. (Halson, et al. 2017)*This deep sleep would therefore be of extreme importance for athletes or those who are physically active, sick, or otherwise undergoing a lot of energy expenditure and tissue breakdown.
After these non-REM stages, you then may fall into REM sleep
Generally occurs after the first 90 minutes of falling asleep, and where the brain becomes more active (i.e. dreams occur during REM sleep)
Heart rate and blood pressure increase and breathing can become quicker and more shallow during this stage.
It is suggested that REM sleep is associated with our learning and memory functions where the brain is consolidating new information and processing it for long term memory. (Halson, et al. 2017)
A typical night should consist of multiple sleep cycles but where the amount of time spent in each stage may depend on the individual, their stage of development (infant, child, adult, etc) and even environmental or situational differences. *There are also multiple moments of wakefulness that we are often unaware of between these cycles throughout the night.
[Below are several consecutive days of my sleep pattern results (obtained from my Fitbit) starting with a Saturday night. *Take note of how different each night looks, despite being consecutive days, and use this for a visual reference for the rest of this post.]
So how much sleep do we actually need?
Sleep researchers often theorize that humans are the only species that actively denies their natural inclination to sleep in favor of work, entertainment, etc.
The behavior of sleep is not only one of the most interesting phenomena that we encounter regularly, it is also arguably the least understood biological function. The little that we do know about sleep, or can at least speculate, is that the behavior itself is necessary for the brain to process and store new data and for the body to recover. It is so valuable to our function that we not only require it regularly, but we require specific amounts on a daily basis. Much of the literature points to a narrow range of 7-8 hours as being most optimal for neurological and physical performance and recovery for the general population, and where less than 7 hours or greater than 8 hours may be associated with adverse health effects. (Sleep, 2015) However, the joint consensus statement from the American Academy of Sleep Medicine and Sleep Research Society states that while adults should sleep 7 or more hours per night, 9 or more hours a night may be needed for:
Those in sleep-debt
Those with illnesses
Other circumstances where there is a larger requirement for physical and neurological growth and development or tissue/immune system repair and recovery
(i.e. ATHLETES...athletes fit this description!)
In fact, there is evidence of increased health risks in those who sleep less than 7 hours or greater than 9 hours (who don't require it) including increased risk for obesity, diabetes, hypertension, heart disease, stroke, and death as well as impaired immune functioning, increased pain, increased errors and accidents, and impaired performance. (Sleep, 2015)
What is even more interesting is the fact that we can make up for lost sleep by accumulating more hours AFTER missing sleep, but we CANNOT store it and save it for later like if we anticipate losing sleep. (We can pay the debt only after we owe, but we can't build credit or savings.)
[If you refer back to my first two nights of sleep: Saturday was a late night with VERY little sleep at all, and NO deep sleep. However, I was able to make up for it on Sunday night with BOTH longer duration and a majority of deep sleep in the first half of the night.]
So what can impact sleep?
Here is just a short list of examples that can impact sleep negatively:
Larger body weight (Abdominal obesity)*
Environment (warm air temperature, humidity)
Light exposure (especially blue light or artificial light)
Late-night screen time
Eating late at night or too close to bedtime
[Truth be told, the last two played a role in my lack of sleep for that Saturday night...!]
*... and not only does a larger body size/obesity interfere with sleep...
This relationship between weight and sleep may be bidirectional where study findings suggest that acute sleep deprivation was associated with a stronger desire for higher calorie foods. (Greer, et al. 2013) In this study, the MORE sleep deprived the participants felt (after going 24 hours without sleep), the greater their desire for high calorie foods compared to when they were in a fully rested state (with an average of 8.2 hours/night for that study group). (Greer, et al. 2013) Additionally, there is a noted decrease in appetite evaluation regions of the frontal cortex associated with sleep deprivation which indicates that there is a diminished ability to accurately assess your appetite (i.e. can't really decide if you are hungry or full). (Greer, et al. 2013) This combination of reduced ability to determine appetite coupled with an increased desire for high calorie foods creates a perfect storm for weight gain and it's associated problems.
...but good nutrition can help to improve sleep!
Nutritional quality can likely play a role in sleep where for example study findings show a correlation between fruit and vegetable consumption and increased sleep duration. (Noorwali, et al. 2018) In this study, the population was separated into:
short sleepers (<7hr/day)
reference sleepers (7-8hr/day) *Most optimal sleep duration for the general population
long sleepers (>8hr/day)
The reference sleepers (7-8hr/day) were associated with eating 28g/day MORE fruits and vegetables than the long sleepers, as well as 24g/day MORE than the short sleepers. (Noorwali, et al. 2018) This implies that the highest fruit and vegetable consumption, and thus proposed highest concentrations of antioxidants (like total carotenoids, B-carotene, and lycopene) were associated with the most optimal 7-8hr/day of sleep whereas those with comparatively LESS fruit and vegetable consumption, and thus less total carotenoids, B-carotene and lycopene, were associated with either less sleep (<7hr/day) or high amounts of sleep (>8hr/day). (Noorwali, et al. 2018) **TAKE NOTE: This is based on sleep recommendations for the general population where <7 or >8 hours/night (for those who don't require longer sleep) was most likely associated with negative health outcomes.
But not only does nutritional quality of the diet matter, nutrient composition may play a role too...
There are several findings, albeit mixed and sometimes inconclusive, regarding the potential impacts of various macronutrient compositions on sleep parameters including:
Sleep efficiency (or the amount of time actually spent sleeping vs just laying in bed)
Sleep latency (or the time it takes you to actually fall asleep after going to bed)
Wake episodes (or the number of times you wake up throughout the night, whether you realize it or not)
Here's a brief review of what some of the research shows:
A high carb/low fat diet showed LESS non-REM sleep (i.e. a DECREASE in your most restorative sleep) compared to a normal balanced diet OR a low carb/high fat diet. (Lindseth, et al. 2013)
[If you refer back to my sleep patterns above, Saturday night and Monday night BOTH happened to include a high calorie/high carb intake right before bed (a lot of low-fat Fro-yo and stale Oreo's...don't judge) AND those are the two nights that happened to have the LEAST amount of non-REM deep sleep.]
Conversely, in an animal study, a high protein diet was associated with significantly enhanced non-REM sleep. (Lindseth, et al. 2013)
Consumption of a protein bar that was rich in tryptophan and with carbohydrates significantly reduced awake time throughout the night in a sample of women. (Lindseth, et al. 2013)
When looking at consumption of very high carbohydrate meals (90% carbohydrates) in young healthy males, high glycemic carbohydrates 4 hours before bed shortened sleep latency (fell asleep SOONER) compared to low glycemic carbohydrates. (Lindseth, et al. 2013) *This could be due to the fact that the high GI carbohydrates had already been digested and absorbed within 4 hours whereas the low GI carbs were still being digested and/or absorbed by bedtime, and thus increased the time to actually fall asleep.
Simiarly, very LOW carbohydrate meals significantly decreased sleep latency (fell asleep sooner). Again, this is likely due to the fact that the carbohydrates are already digested by bedtime (4 hours after the meal) and thus are not providing fuel to the body and brain which may extend sleep latency, or the time to actually fall asleep.
Also, foods that provide a high thermic effect of feeding (increased body heat losses due to digestive processes) like high protein or high calorie meals, can actually INCREASE sleepiness due to the increased heat loss occurring from the metabolism of those nutrients. (Lindseth, et al. 2013) *Hence why eating a high calorie or high protein meal makes us feel tired afterwards; we are using extra energy to metabolize those nutrients, leaving us feeling tired or fatigued for up to 2 hours after that meal.
There are multiple study findings to suggest that high fat intake was associated with either long sleep duration (over 8 hours for those who don't need it) or short sleep duration (less than 7 hours). *BOTH of which are associated with negative health outcomes in the general population. Take note: this was likely based on a chronic high fat diet characteristic of the 'Standard American Diet'.
It should go without saying that caffeine and alcohol both negatively impact sleep where caffeine is a stimulant and thus will INCREASE sleep latency (takes longer to fall asleep) AND disrupts sleep. (Lindseth, et al. 2013) Alcohol can actually decrease sleep latency (fall asleep sooner) HOWEVER it interrupts BOTH REM and non-REM sleep cycles (poor sleep quality and efficiency). (Lindseth, et al. 2013)
High protein intake, especially before bed, may help to improve sleep
Carbohydrates should likely be eaten far enough away from sleep (~4 hours before sleep)
High fat intake may be associated with poor sleep
Try to avoid caffeine and alcohol anywhere near bedtime
...and if you're curious as to why protein is so good for sleep...
Protein, or amino acids, among many roles are necessary for neurotransmitter synthesis. When it comes to sleep, the primary hormone melatonin is actually a product of the neurotransmitter serotonin. When there is an absence of light, serotonin is converted into melatonin which promotes sleep. Now a majority of serotonin in the body is produced in the gut but it is the brain-derived serotonin that most likely plays a role in sleep, and it is produced from the amino acid tryptophan. Tryptophan is found in many foods, most famously in animal proteins like dairy, poultry, beef, and fish, but also in soy and tofu, seeds like sesame seeds, and oats, to name a few. [This is where that theory of tryptophan from Thanksgiving turkey gets it's reputation for making us tired, but in reality it's more likely the high thermic effect of feeding from high protein and high calorie intake increasing drowsiness as noted above.]
Take from this what you will, but never stop learning.
Asif N, Iqbal R, Nazir C. Human immune system during sleep. American Journal of Clinical and Experimental Immunology. 2017; 6(6):92-96. https://www-ncbi-nlm-nih-gov.proxy.lib.fsu.edu/pmc/articles/PMC5768894/
Greer S, Goldstein A, Walker M. The impact of sleep deprivation on food desire in the human brain. Nature Communications. 2013; https://www-ncbi-nlm-nih-gov.proxy.lib.fsu.edu/pmc/articles/PMC3763921/
Halson S, Juliff L. Sleep, sport, and the brain. Progress in Brain Research. 2017; 234:13-31. https://www-ncbi-nlm-nih-gov.proxy.lib.fsu.edu/pubmed/29031461
Lindseth G, Lindseth P, Thompson M. Nutritional Effects on Sleep. Western Journal of Nursing Research. 2013; 35(4): 497-513. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5621741/
Noorwali E, Cade J, Burley V, et al. The relationship between sleep duration and fruit/vegetable intakes in UK adults: a cross-sectional study from the National Diet and Nutrition Survey. BMJ Open. 2018; 8(4): https://www-ncbi-nlm-nih-gov.proxy.lib.fsu.edu/pmc/articles/PMC5922510/
Recommended Amount of Sleep for a Healthy Adult: A Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society. Sleep. 2015; 38(6): 843-844. https://academic.oup.com/sleep/article/38/6/843/2416939
Ritsche K, Nindl B, Wideman L. Exercise-Induced growth hormone during acute sleep deprivation. Physiological Reports. 2014; 2(10): https://www-ncbi-nlm-nih-gov.proxy.lib.fsu.edu/pmc/articles/PMC4254093/
Tamaki M, Huang T, Yotsumoto Y, et al. Enhanced Spontaneous Oscillations in the Supplementary Motor Area Are Associated with Sleep-Dependent Offline Learning of Finger-Tapping Motor-Sequence Task. The Journal of Neuroscience. 2013; 33(34): 13894-13902. https://www-ncbi-nlm-nih-gov.proxy.lib.fsu.edu/pmc/articles/PMC3755724/