For better sleep we should go back to the Stone Age

Is sleep one of the few things that we actually did better in the Stone Age? To answer this question we spoke with a sleep expert.

Christoph Nissen whose paper “Prolonged Sleep under Stone Age Conditions” was one of the top trending articles on ResearchGate last week. The article saw Nissen and his team study a Stone Age experiment on a German science TV show. Nissen is the Medical Director of the Sleep Laboratory at the University of Freiburg, Germany.

ResearchGate: How did you come to focus on Stone Age sleep conditions?

Christoph Nissen: Sleep problems are among the most prevalent health problems worldwide. Moreover, chronic sleep difficulties have been linked to an increased risk in developing major disorders, such as cardiovascular disease or depression. Some authors feel that the high prevalence of sleep difficulties in society is connected with modern living conditions, including artificial light and high media use, but experimental evidence was sparse or lacking.

This experiment gave us the unique opportunity to assess sleep-wake behavior over several weeks under "stone-age" conditions in the absence of any technical devices or other modern living conditions. With some limitations, the results support the notion that people under "stone age conditions" slept earlier and longer. Our data also increased awareness of the detrimental impact of excessive light and electronic device use in the late evening.

RG: You expected people to go to bed earlier and sleep longer when living in Stone Age conditions. Where did these expectations come from?

Nissen: These expectations were derived from experimental laboratory data that showed that the absence or reduction of light can help us fall to sleep earlier by advancing sleep phases. However, before our study the translation of these lab observations to real world conditions had been largely lacking.

RG: People in your Stone Age experiment were going to sleep nearly 2 hours earlier. Was this number surprising?

Nissen: Yes, the extent was surprising! 2 hours is very substantial in sleep medicine; for instance widely used hypnotics such as benzodiazepines (e.g. diazepam) or benzodiazepine receptor agonists (Z-substances, such as zopiclone or zolpidem) tend to prolong sleep by only 30 min. Furthermore, the effectiveness of these hypnotics actually diminishes over time.

RG: Having no exposure to artificial light and no access to electronic media was one of the explanations for people going to sleep earlier. Why was this the case?  

Nissen: Yes, light is the strongest "Zeitgeber" in animals and humans. This means that light exposure to our eyes (retina) is transferred into an internal chemical signal (melatonin from the pineal gland) that determines the circadian phase of our sleep wake rhythm. Light exposure in the evening, including light from electronic devices such as computer screens or smart phones, leads to a delayed onset of the melatonin secretion (melatonin is an internal signal that facilitates sleep). This in turn leads to prolonged wakefulness and a preference for a phase delay of the sleep phase (going to bed later).

Delayed sleep onset together with the frequent need to get up early (due to job-related or social constraints) leads to a reduction in total sleep time. This can increase the risk of cognitive impairment, emotional dysregulation or even associated disorders, such as cardiovascular disease or mental disorders like depression.

RG: Another reason for people going to bed earlier and getting more sleep in Stone Age conditions was “social interaction”. Can you explain how this works?

Nissen: Social interaction is, after light, the second most important "Zeitgeber" for circadian rhythm in humans. The social synchronization of sleep-wake behavior determined by the natural light-dark cycle can facilitate a stable circadian rhythm in social groups (without individuals in the group being exposed to artificial light). This can promote an earlier and longer sleep phase.

RG: The people in your prehistoric experiment didn’t suffer from things like starvation and various other stress factors that would have been a part of real Stone Age life. Did this affect the results?

Nissen: I believe that under real Stone Age conditions that do include various stressors, we would not have observed an effect that is as substantial as the 2 hours observed in our experiment. In other words, I would expect that the basic findings in form of a phase advance of sleep onset would still persist, but that the overall effect would be diminished.

RG: What recommendations would you give to improve sleep in the modern world?

Nissen: I would recommend that people limit their media exposure and use of artificial light in the evening, for instance they should either completely avoid it or use it very sparingly from 9 or 10 pm onwards!

RG: Would it be a good idea for people to sleep like they did in the Stone Age?

Nissen: I am very happy to live under modern conditions and I think we have many benefits. I just think people should reflect on the price of some of these advancements and find active solutions. In this case, people need to actively plan and self-limit their use of these beautiful technical devices such as smart phones in the evening.

Image courtesy of Flominator