SANTA CLARA, California, February 26. SLEEP deprivation occurs in all modern human populations and is exacerbated in western culture. In swimming, morning workouts are anecdotally associated with success, but do these benefits outweigh the risks? This is the ultimate goal of this series.
For a review of sleep phases, what initiates sleep, and the prevalence of disturbed sleep, please read the previous two installments (Part I, Part II). This section takes a step-by-step approach covering all the physiological consequence of sleep deprivation on health and injury.
Sleep Deprivation and Inflammation
Despite the negative connotation, it seems the acute inflammatory response aids strength gains (read about Inflammation in Sports). However, chronic inflammation due to injury or stress is implicated in numerous diseases (cardiovascular disease, diabetes, etc.). More importantly (to athletes), chronic inflammation may alter leukocyte levels and increase the risk of illness (Vozarova 2002).
The current relationship between sleep and chronic inflammation is unclear, as many inflammatory mediators exist (including tumour necrosis factor-a (TNF- a) and C-Reactive Protein (CRP), our focus here). At this time, the association between sleep and CRP remains equivocal, as studies in the past decade show opposing results (Taheri 2007; Lainonen 2007; Miller 2009).
Thus, more research is clearly required before any associations between sleep deprivation and CRP can be delineated.
However, in populations of disturbed sleepers, including those who suffer from insomnia and sleep apnea (hopefully both uncommon in swimmers), elevations in inflammatory markers are evident (Burgous 2006; Vgontzas 2002). If inflammation does result of sleep deprivation, modulators of inflammation (prostaglandins and cytokines) may sensitize receptors of pain (nociceptors), perhaps supporting the notion that sleep deprivation increases perception of pain (Watkins 2005). Indeed, sleep deprivation in healthy adults elicits self-reported, generalized pain, yet this pain may be correlate with, not cause pain (Hack 2009). Studies on athletes are still pending, especially in youth athletes.
Unfortunately, there is a paucity of research examining sleep deprivation and inflammation in women, a necessity, as differences between the sexes have often not been studied (Meier-Ewert, 2010). Some studies suggest that sleep deprivation may produce stronger inflammatory responses in women (e.g. Irwin 2008). With respect to specific inflammatory modulators, restricting sleep by roughly a quarter of customary levels produced increased inflammatory signalling levels in men and women alike, but only men showed increases in inflammatory markers (Vgontzas 2004). Nonetheless, sleep deprivation appears to increase the risks of illness and sensitize pain, both which influence training adaptations.
Influence of Immune Modulators on Sleep
The presence of inflammatory modulators can significantly alter sleep, as reports suggest injections of inflammatory modulators alters sleep (Imeri 2009).
Effects of Sleep Quality and Quantity on Immune Modulators
Individual immune responses to sleep deprivation exist and are dependent on many factors like age, sex and other demographic factors (Vgontzas 2004). An association between sleep deprivation and immunity has been documented for a long time. Fifty years ago, 5 days of sleep deprivation increased white blood cell count, suggesting a response of defense (Kuhn 1969; Born 1997). Sleep deprivation appears to only alter specific white blood cells, monocytes and neutrophils, not lymphocytes. Moreover, sleep deprivation studies have demonstrated elevations in other immune system modulators (IL-1ß, IL-6, and TNF- a) (Dinges 1995). Unfortunately, reproductions of these responses do not exist (Shearer 2001).
For years, many have felt there is an association between sleep and vulnerability. Recently, a study exposed participants to a rhinovirus and monitored their health for 5 days. Most of the subjects became infected with the virus, more than a third had cold-like symptoms. Individuals sleeping less than 7 hours per night for 2 weeks before exposure were three times more likely to have symptoms than those who slept for more than 8 hours (Cohen 2009). Moreover, sleep efficiency, the percent of time actually sleeping in bed, compared to just lying in bed, was strongly correlated with cold susceptibility.
Sleep on Injury
Injuries occur at every level of all sports. However, a study surveyed over a hundred high school athletes and adolescent athletes who slept eight or more hours each night were 68 percent less likely to be injured than athletes who regularly slept less (Milewski 2012).
Hopefully, this detailed review provided you information on the necessity of sleep for staying healthy. The next installment will discuss how sleep alters training and performance.
G. John Mullen is the owner of the Center of Optimal Restoration and creator of Swimming Science. He received his Doctorate in Physical Therapy at the University of Southern California. G. John has been featured in Swimming World Magazine, Swimmer Magazine, and the International Society of Swim Coaches Journal.