In humans, a mild stimulation of the primary host defense has negative effects on emotional and memory functions, which are probably caused by cytokine release. Hence, cytokines represent a novel target for neuropsychopharmacological research.

Sleep and immunity are bidirectionally linked. Immune system activation alters sleep, and sleep in turn affects the innate and adaptive arm of our body’s defense system. Stimulation of the immune system by microbial challenges triggers an inflammatory response, which, depending on its magnitude and time course, can induce an increase in sleep duration and intensity, but also a disruption of sleep. Enhancement of sleep during an infection is assumed to feedback to the immune system to promote host defense. Indeed, sleep affects various immune parameters, is associated with a reduced infection risk, and can improve infection outcome and vaccination responses. The induction of a hormonal constellation that supports immune functions is one likely mechanism underlying the immune-supporting effects of sleep. In the absence of an infectious challenge, sleep appears to promote inflammatory homeostasis through effects on several inflammatory mediators, such as cytokines. This notion is supported by findings that prolonged sleep deficiency (e.g., short sleep duration, sleep disturbance) can lead to chronic, systemic low-grade inflammation and is associated with various diseases that have an inflammatory component, like diabetes, atherosclerosis, and neurodegeneration. Here, we review available data on this regulatory sleep-immune crosstalk, point out methodological challenges, and suggest questions open for future research.

That insufficient sleep is associated with poor attention and performance deficits is becoming widely recognized. Fewer people are aware that chronic sleep complaints in epidemiological studies have also been associated with an increase in overall mortality and morbidity. This article summarizes findings of known effects of insufficient sleep on cardiovascular risk factors including blood pressure, glucose metabolism, hormonal regulation and inflammation with particular emphasis on experimental sleep loss, using models of total and partial sleep deprivation, in healthy individuals who normally sleep in the range of 7-8 hours and have no sleep disorders. These studies show that insufficient sleep alters established cardiovascular risk factors in a direction that is known to increase the risk of cardiac morbidity.

Insufficient sleep quantity may facilitate and/or exacerbate pain through elevations of IL-6. In disorders where sleep disturbances are common, insufficient sleep quantity itself may establish and maintain its co-occurrence with pain and increased inflammation.

Controlled, experimental studies on the effects of acute sleep loss in humans have shown that mediators of inflammation are altered by sleep loss. Elevations in these mediators have been found to occur in healthy, rigorously screened individuals undergoing experimental vigils of more than 24 hours, and have also been seen in response to various durations of sleep restricted to between 25 and 50% of a normal 8 hour sleep amount. While these altered profiles represent small changes, such sub-clinical shifts in basal inflammatory cytokines are known to be associated with the future development of metabolic syndrome disease in healthy, asymptomatic individuals. Although the mechanism of this altered inflammatory status in humans undergoing experimental sleep loss is unknown, it is likely that autonomic activation and metabolic changes play key roles.

The data suggest that chronic insufficient sleep may contribute to the onset and amplification of pain and affect health by compromising optimistic outlook and psychosocial functioning.

Pain can be both a cause and a consequence of sleep deficiency. This bidirectional relationship between sleep and pain has important implications for clinical management of patients, but also for chronic pain prevention and public health more broadly. The review that follows will provide an overview of the neurobiological evidence of mechanisms thought to be involved in the modulation of pain by sleep deficiency, including the opioid, monoaminergic, orexinergic, immune, melatonin, and endocannabinoid systems; the hypothalamus-pituitary-adrenal axis; and adenosine and nitric oxide signaling. In addition, it will provide a broad overview of pharmacological and non-pharmacological approaches for the management of chronic pain comorbid with sleep disturbances and for the management of postoperative pain, as well as discuss the effects of sleep-disturbing medications on pain amplification.

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