Sleep, social relationships and the brain
Bruce S. McEwen, Ph.D., The Rockefeller University
Sleep is a precious commodity that is often sacrificed by the pace of modern life and the compromises that go with it. Loss of sleep can cause a number of neurochemical and physical changes in the brain and, as a stressor, can dysregulate physiological processes that affect health and well-being, including increased incidence of obesity. Loss of sleep can increase overeating of comfort food, impair memory and decision making and depress mood. Current busy lifestyles, including less sleep time, contribute to increases in modern-day illnesses like diabetes, depression and cardiovascular disease. One contributing factor is likely to be increases in loneliness and a failure to make and/or maintain meaningful social relationships.
Recent research by Elliot Friedman and colleagues at the University of Wisconsin has shown that poor social connectedness is associated with elevated levels of an inflammatory cytokine, interleukin 6, which is a chemical signal of the immune defense system of the body that, on the one hand, helps activate immune defense responses but which, on the negative side, is also chronically elevated in many of the disorders of modern life such as cardiovascular disease, diabetes, arthritis, degenerative brain diseases and depression. Elevated levels of these cytokines may affect the brain, since a recent study by Anna Marsland and coworkers at the University of Pittsburgh has shown that elevated levels of an inflammatory cytokine, Interleukin-6, are associated with smaller volume of a brain structure, the hippocampus, that is essential for key aspects of memory formation, as well as mood regulation.
In the Friedman study, poor sleep was also associated with elevated levels of interleukin 6. Sleep is believed to be a brain state during which consolidation of memories is taking place. For example, during this time, the brain solidifies memories of where we were and what we were doing when something of importance happened. Sleep deprivation is a stressor that increases the homeostatic drive to sleep, and sleep reduces interleukin 6 and replenishes stores of energy in the form of glycogen in the brain that are depleted by lack of sleep.
The long-term consequences of sleep deprivation and disruption of our day-night rhythm by shift work and jet lag constitute a form of chronic stress (also called “allostatic load”) – with physiologic imbalances involving hypertension, reduced parasympathetic tone, increased inflammatory cytokines, increased oxidative stress, and increased evening cortisol and insulin, all of which are signs that the body is out of balance. Reduced sleep is associated with increased risk for obesity, which also means increased chances of cardiovascular disease and Type 2 diabetes. Indeed, shorter sleep times, which are progressively part of the lives of Americans and other nationalities, have been associated with increased obesity.
As a result of the common type of diabetes (called Type 2 diabetes) that is increasingly prevalent in many societies, there is also poorer cognitive function, as well as increased risk for depression and increased risk for Alzheimer’s disease. Disruptions of our biological clocks that synchronize us with the light:dark cycle, is a broader aspect of the problem of sleep disruption. Shift work and jet lag are two common practices that have measurable effects on the brain and body. Long distance air travel with short turnaround has been reported to be associated with smaller volume of the temporal lobe, which includes the hippocampus, and impaired performance on a visual-spatial cognitive task.
As Americans have become disconnected from core families and communities to pursue their lives and careers, often in places distant from their birthplaces, one of the unintended consequences is loneliness and isolation. These have been described first by Robert Putnam in Bowling Alone and very recently by Jacqueline Olds and Richard Schwartz in their book, The Lonely American. Indeed, the fast pace of life, job and career pressures and long working hours often leads to a need for privacy, followed by a sense of exclusion and loneliness and leads to reduced time for social interactions with friends and the building of healthy relationships. Moreover, for those who have caregiving responsibilities, there is chronic stress that has consequences for the brain and body and that also can preclude social interactions outside the home.
The good news is that positive relationships and social networks buffer against stressors, such as sleep deprivation, by providing an emotional outlet and other types of social support, thereby reducing the burden of chronic stress and allostatic load from such common stressors as work and caregiving. Better sleep is one of the consequences of improved mood and reduced anxiety. Volunteer programs such as the Experience Corps, provide opportunities for social interactions outside of the home and also give meaning and purpose in life for participants, and they have been shown to benefit the physical and mental health of those who are involved in the program.
Further Reading:
Arvanitakis Z, Wilson RS, Bienias JL, Evans DA, Bennett DA (2004) Diabetes mellitus and risk of Alzheimer disease and decline in cognitive function. Arch. Neurol. 61:661-666.
Atkinson G, Davenne D (2007) Relationships between sleep, physical activity and human health. Physiol. & Behav. 90:229-236.
Cho K (2001) Chronic ‘jet lag’ produces temporal lobe atrophy and spatial cognitive deficits. Nature Neurosci. 4:567-568.
Fried LP, Carlson MC, Freedman M, Frick KD, Glass TA, Hill J, McGill S, Rebok GW, Seeman T, Tielsch J, Wasik BA, Zeger S (2004) A social model for health promotion for an aging population: Initial evidence on the experience corps model. J. Urban Health: Bull NY Acad. Med. 81:64-78.
Friedman EM, Hayney MS, Love GD, Urry HL, Rosenkranz MA, Davidson RJ, Singer BH, Ryff CD (2005) Social relationships, sleep quality, and interleukin-6 in aging women. Proc. Natl. Acad. Sci. USA 102:18757-18762.
Gais S, Born J (2004) Declarative memory consolidation: Mechanisms acting during human sleep. Learning & Memory 11:679-685.
Gangwisch JE, Malaspina D, Boden-Albala B, Heymsfield SB (2005) Inadequate sleep as a risk factor for obesity: analyses of the NHANES I. Sleep 28:1289-1296.
Hendrickx H, McEwen BS, van der Ouderaa F (2005) Metabolism, mood and cognition in aging: The importance of lifestyle and dietary intervention. Neurobiol. Aging 26S:S1-S5.
Marsland AL, Gianaros PJ, Abramowitch SM, Manuck SB, Hariri AR (2008) Interleukin-6 covaries inversely with hippocampal grey matter volume in middle-aged adults. Biol. Psychiat. 64:484-490.
McEwen BS (1998) Protective and Damaging Effects of Stress Mediators. New England J.Med. 338:171-179.
McEwen BS (2007) Physiology and neurobiology of stress and adaptation: Central role of the brain. Physiol. Rev. 87:873-904.
Olds J, Schwartz RS. The Lonely American: Drifting Apart in the 21st Century Beacon Press, Boston, 1998.
Putnam RD. Bowling Along: The Collapse and Revival of American Community. New York: Simon & Schuster, 2000.
Seeman TE, Singer BH, Ryff CD, Dienberg G, Levy-Storms L (2002) Social relationships, gender, and allostatic load across two age cohorts. Psychosom. Med. 64:395-406.
Tasali E, Leproult R, Ehrmann DA, Van Cauter E (2008) Slow-wave sleep and the risk of type 2 diabetes in humans. Proc. Natl. Acad. Sci. USA 105:1044-1049.
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