The influence of sleep reduction/deprivation, its effects on the immune system and athletic performance and recovery.
Sleep is a well known to be an important factor in the repair of damaged tissue within the body. Whether that be through exercise, illness or natural processes it’s a vital component and its suggested should comprise at least 1/3 of the day.
But what is sleep? At a basic level sleep is a lack of conscious processes, sensory activity and a reduction in activity of voluntary muscles (1).
Throughout the day the brains neurotransmitters levels fluctuate in accordance with the natural circadian rhythm causing drowsiness and eventually sleep. Comprised of 2 main stages NREM and REM it can be further broken down but for the purpose of this article, we will consider sleep as a whole. It's also worth considering what do the terms Sleep Deprivation (SD) and Sleep Reduction (SR) mean?
Sleep reduction is related to falling asleep later or waking up earlier than the normal circadian rhythm would allow. Typically only considered a reduction worthy of note should it be more than 2.5 hours per night it’s a partial disturbance of one or more sleep cycles (6). Sleep deprivation, on the other hand, is more dramatic and refers to extreme cases of sleep loss where an individual doesn’t sleep for more than 24 hours at a time (6).
During this restful period, it's noted that changes occur in almost all human physiological processes and permit recovery from previous wakefulness and/or prepare for functioning in the subsequent wake period (2). Within the immune system, the circadian rhythm is a regulator of immunological processes with immune functions coordinating to with the regular 24-hour sleep-wake cycle.
Varying Leukocytes peak throughout this circadian rhythm with differentiated immune cells such as cytotoxic NK peaking during the wake period they are better able to destroy intruding antigens and repair tissues damaged during conscious activities (3). In contrast, less well-differentiated cells such as Memory T cells peak at night, working when the slowly evolving adaptive immune response is activated.
Beyond the immune system the body’s natural homeostasis is also dependent on the release of chemicals in accordance with the circadian rhythm (3). Growth hormones and prolactin are abundant during the Slow Wave Sleep (SWS - Deep Sleep) stages of the sleep cycle while the stress hormone cortisol is at its lowest meaning repair of damaged bodily tissues can occur at a higher anabolic rate (3, 4).
Withdrawal of sleep or variation of circadian rhythm creates a stress response releasing pro-inflammatory cytokines into the blood stream (3). This leads too a systemic low grade inflammation coupled with the a reduction in immune system function that increases the bodies susceptibility to pathogens (3). In short, reduced, deprived or altered sleep patterns reduce the bodies immune defense and increase the likelihood of becoming unwell.
The circadian rhythm can be upset by a number of factors many of which are experienced by elite athletes and recreational participants. They include the use of stimulants such as caffeine, timing of meals, and intense exercise prior to bed. It’s recorded that while elite athletes spend longer in bed than the average person they took longer to fall asleep and had a lower quality of sleep (5).
This reduction in sleep and the biological cascade of effects it sets in motion can alter the performance of the athlete both physical and psychologically although variations in chosen sport do show differences in the reduction of performance.
In intense endurance sports such as long distance running it was found that participants ran slower during a self pacing 30min run when sleep deprived than when rested (7). This is offset by no apparent reduction in endurance running performance when suffering sleep reduction. In the absence of any physiological evidence its thought this is down to a psychological fatigue caused by the deprivation, altering the perception of perceived effort slowing the athlete (8).
Picking a more acute sport there’s little evidence to suggest sleep deprivation has an affect on competitive weight lifting. Studies comparing a variety of lifts and training methods found no difference in strength when rested and after 30hours of sleep deprivation (9). It’s considered that this may be due to the bodies ability to replace growth hormones usually secreted at night throughout the next day. In reverse to the previous example sleep reduction over a number of consecutive nights has been shown to reduce maximal and sub maximal strength in benching, leg press and dead lifts. This is attributed again too perceptual changes in strength but its also considered to be accompanied by neuromuscular fatigue (10).
While research into elite athletes is scarce a trend is clear from that available. Endurance sports tend to be greater affected by that of sleep deprivation where as power based sports suffer in consecutive days of sleep reduction.
With sleep playing such a vital role in athletic performance it’s important to get enough, even if in fragments. Those who struggle with sleep deprivation through insomnia or sleep reduction may benefit from daytime napping arranged around their training (12). Studies based around athletic performance and napping have shown an increase in power, speed and alertness when completed after a 30 minute nap and cognitive performance is also increased with napping prior to exercise (12). Napping soon after training has been shown to help in committing learned motor skills and tactics to memory, maintains neuroplasticity within the brain, while improving the recovery rate of the athlete (12).
For those who struggle to sleep there are a range of supplements on the market aimed at helping ease the body into a deep sleep.
Supplementation of tryptophan has been shown to improve both sleep latency and quality (13). Tryptophan is a precursor essential amino acid to the neurotransmitters 5-HT, serotonin and melatonin, all neurotransmitter directly linked with inducing sleep. Consuming just 1g a day should be enough to have an affect, and being readily available through 300g of turkey meat or 200g of sunflower seeds its easily obtainable (13).
Melatonin is a hormone involved in inducing sleep, it recognizes the onset of darkness and has some promising applications in insomniacs (15). Foods rich in melatonin such as cherries, grapes and bananas may be used to boost the bodies levels and decreased the time taken to fall asleep. Research tested and approved concentrated cherry juice is used in treating insomniacs by decreasing the onset of sleep as mentioned above (14). Its worth considering melatonin can cause harm in high doses with side effects including headaches, nausea and nightmares (16).
Other traditional remedies such as lavender oil, magnesium, lemon balm and many, many more are commonly used, but currently not backed by a wealth of evidence so have been excluded from this.