How Much Sleep is Enough?

A new German study provides further evidence that approximately 7 hours or sleep seems to be an optimal amount for many individuals, and that too much or too little sleep can contribute to health problems.

Throughout a 2-month period, a team of researchers from University Medical Center Freiburg assessed a group of 5 healthy adults placed in “a Stone Age-like settlement,” without electricity, clocks, or running water, in an effort to investigate the impact of prehistoric living conditions on sleep-wake behavior.
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The most notable finding, according to the authors, was that “nocturnal time in bed and estimated sleep time, as measured by actigraphy, markedly increased during the experimental period compared to the periods prior to and following the experiment.” These increases were primarily driven by a phase-advance shift of sleep onset, according to the investigators, who note that subjective assessments of health and functioning did not reveal any relevant changes across the study. In the study, participants fell asleep about 2 hours earlier and got an average of about 1.5 more hours sleep than in their normal lives. Their average amount of sleep during the study was approximately 7.2 hours per night.

The findings build on those of past studies, which have found that approximately 7 hours of nightly sleep is an ideal amount. For example, a 2002 study of 1.1 million people, conducted by University of California San Diego researchers, found people who reported they slept 6.5 hours to 7.4 hours had a lower mortality rate than those with shorter or longer sleep. Last year, University of Michigan and Duke University researchers analyzed the self-reported sleeping habits of about 160,000 users who took spatial-memory and matching tests, and about 127,000 users who took an arithmetic test, finding that cognitive performance increased as people got more sleep, reaching a peak at 7 hours before starting to decline.

Primary care physicians “should inform patients that an individually appropriate amount of sleep—the sleep duration on weekends and vacation days—is highly important for somatic and mental health,” says Christoph Nissen, MD, medical director of the sleep laboratory at University Medical Center Freiburg, and co-author of the school’s recent sleep study.

For instance, a shorter sleep duration—due to societal, professional, familiar, or other pressures—will in the long run be associated with an increased risk for developing major depression, cardiovascular disease, metabolic problems such as obesity, immune dysfunction, and cognitive deficits for those with substantial and chronic sleep problems, says Nissen.

Targeted sleep interventions might have the potential to decrease the risk for developing such health problems, he says, adding that “standard sleep medication such as benzodiazepines or benzodiazepine agonists have a high risk [of inducing] tolerance effects, the development of dependency, and [not] fostering the important functions of sleep.”

—Mark McGraw

Reference

Piosczyk H, Landmann N, et al. Prolonged sleep under Stone Age conditions. J Clin Sleep Med. 2014.

Kripke D, Garfinkel L, et al. Mortality Associated With Sleep Duration and Insomnia. Arch Gen Psychiatry. 2002.

Sternberg D, Ballard K, et al. The largest human cognitive performance dataset reveals insights into the effects of lifestyle factors and aging. Front Hum Neurosci. 2013.