The precise role of sleep in animals, including humans, remains unknown. As children, our parents shout at us to get more sleep. As parents, we often find ourselves complaining we don't get enough sleep. And yet, the precise function of sleep remains undetermined, and much of our perception of the role of sleep stems from our understanding of the consequences of sleep deprivation or poor sleep quality on our well-being.
In a recent study by Prather and colleagues published in September's issue of SLEEP (1), investigators examined the effects of sleep deprivation on our immune system's ability to stave off infection. Cleverly, the investigators inoculated the common cold virus into the noses of adult volunteers using nasal drops and then examined the role of sleep duration in the susceptibility of developing a frank cold. Total sleep was defined objectively using actigraphy -- a device worn on the wrist that differentiates wake from sleep according to algorithms that measure body movement.
The investigators discovered that following inoculation of the cold virus, those who slept less than 5 hours had a 4.5 times greater chance of developing a frank cold. Those that slept 5-6 hours had a 4.24 times greater chance of developing a frank cold, compared to those volunteers who slept greater than 7 hours (the recommended duration of sleep by the National Sleep Foundation) (*). The effect of sleep duration remained significantly associated with developing a cold following control of many other relevant risk factors including season, smoking history, and stress levels.
This is the first study to examine the effects of sleep duration on the body's ability to fight infection by objectively measuring sleep duration. Previous studies linking vulnerability to infections and sleep duration have relied on subjective reporting (2, 3). Thereby, this study is not susceptible to reporter bias. This is not the first study however, linking sleep duration and the strength of our immune system. Adequate sleep is critical to training our immune system's response following vaccination (4, 5). That is, not getting enough sleep will potentially reduce the efficacy of a vaccine. Further clarifying the association of sleep and the immune system has shown that sleep deprivation does lead to alterations in the population of specific circulating immune cells that are typically involved in fighting infection (6).
Interestingly, one of the consequences of illness includes sleepiness. Certain circulating cytokines, substances that are secreted by immune cells that help orchestrate the immune system to fight infection, can also stimulate the brain towards sleep (7). Conceivably, our immune system is informing the brain to sleep more in order to strengthen itself to fend off the infection.
Taken together, the evidence thus far seems to strongly suggest that inadequate sleep duration increases the likelihood of becoming ill following an infection and hinders our body's ability to fight infection. Conversely, getting enough sleep may be one of our most powerful antibiotics to keep us healthy. Our parents were right!
1. Prather AA, Janicki-Deverts D, Hall MH, Cohen S. Behaviorally Assessed Sleep and Susceptibility to the Common Cold. Sleep 2015.
2. Patel SR, Malhotra A, Gao X, Hu FB, Neuman MI, Fawzi WW. A prospective study of sleep duration and pneumonia risk in women. Sleep 2012; 35: 97-101.
3. Cohen S, Doyle WJ, Alper CM, Janicki-Deverts D, Turner RB. Sleep habits and susceptibility to the common cold. Arch Intern Med 2009; 169: 62-67.
4. Lange T, Perras B, Fehm HL, Born J. Sleep enhances the human antibody response to hepatitis A vaccination. Psychosom Med 2003; 65: 831-835.
5. Spiegel K, Sheridan JF, Van Cauter E. Effect of sleep deprivation on response to immunization. JAMA 2002; 288: 1471-1472.
6. Irwin M, McClintick J, Costlow C, Fortner M, White J, Gillin JC. Partial night sleep deprivation reduces natural killer and cellular immune responses in humans. FASEB J 1996; 10: 643-653.
7. Kapas L, Krueger JM. Tumor necrosis factor-beta induces sleep, fever, and anorexia. Am J Physiol 1992; 263: R703-707.
Also on The Huffington Post: