Chronotypes: Sleep “Fingerprints,” “Social Jet Lag,” and Health

-*Are you out of sync with socially-defined time at work and home?

Most people require about one hour of sleep for every two hours awake, and each hour of missed sleep results in deeper sleep until the “sleep debt” is resolved.
Health and safety problems of varying severity ensue when the sleep debt is unresolved.

Till Roenneberg

Till Roenneberg

Till Roenneberg of Ludwig-Maximilians-University Munich investigated these health consequences by studying variances individual sleep “chronotypes,” or the amount of elapsed time until a person reaches midsleep,”  the midpoint between average bedtime when not determined by schedule requirements and waking time.

His Internal Time: Chronotypes, Social Jet Lag, and Why You’re So Tired reported one less-known health consequence of discrepant chronotypes – greater likelihood of smoking. Internal Time
Roenneberg found that greater than 60 percent of those with more than five hours social jet lag are smokers and they have greater difficulty changing this habit than those with less social jet lag.

David Randall

David Randall

Journalist David K. Randall experienced an episode of sleepwalking and documented his quest to learn more about sleep in his Dreamland: Adventures in the Strange Science of Sleep.
In it, he points out that sleep is crucial for muscle regeneration and long-term memory formation, and conversely, sleep loss interferes with these critical functions.

Other negative consequences of sleep disruption are even more dire.Dreamland
He reported that depression rates are forty times higher for people with insomnia than those without sleep problems, and that sleep apnea causes 38,000 fatal heart attacks and strokes in the United States each year.

The difference between the personal chronotype and socially-defined time can be considered “social jet lag” that can lead to chronic exhaustion.
Roenneberg calculates that more than 40 percent of the Central European population experiences more than two hours of social jet lag, which can lead to increased errors at work and in operating equipment like automobiles. These consequences can be critical when the work involves public safety in transportation and health care settings.

Adolescents generally experience considerable social jet lag because their average midsleep point is later than that of many adults, and is incompatible with typical school start times.
This is because typical adolescent brains release the hormone melatonin around eleven o’clock at night until after the seasonal sunrise.
In contrast, adults, who set school schedules, have minimal levels of melatonin in their bodies when they wake in the morning, so they are more likely to feel and act alert in the early morning.

Sleep, then, has both physiological and cultural determinants, as Roenneberg showed in his analysis of agrarian areas which may not have such technologies as electric lighting, Day Light Saving Time, or work-related reasons for early rising.
These people typically go to sleep earlier and awake earlier than urban dwellers, and have significantly different midsleep points than people in cities.

A. Roger Ekirch

A. Roger Ekirch

Historian A. Roger Ekirch of Virginia Polytechnic Institute and State University argues in At Day’s Close: Night in Times Past, that before the Industrial Revolution, the typical sleep pattern was “segmented sleep” (also known as divided sleep, bimodal sleep pattern, or interrupted sleep).

People slept for two or more periods (called “first sleep” or “dead sleep” and “second sleep” or “morning sleep”) in medieval England, punctuated by a period of wakefulness.
Similar terms are found in terms French and Italian languages and among the Tiv of Nigeria.

At Days CloseHe argues that this is the natural pattern of human sleep, and is important in regulating stress.
If this is accurate, it would change western medical diagnosis of sleep disorders and might change expectations of “normal” sleep patterns for optimal health and productivity.

Ekirch’s review of historical records suggests that agrarian people were exhausted after field labor, so they would eat and go to sleep quickly after stopping work.
They would later awaken later to pray, reflect, have sex, perform manual labor, interpret dreams, visit neighbors, or engage in petty crime.
Scholars, in contrast, used this time for loftier pursuits –  to write without interruption.

-*How do you manage segmented sleep and social jet lag?

Related post:
Kept Up at Night by Intrusive Thoughts of Work: Elusive Sleep

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7 thoughts on “Chronotypes: Sleep “Fingerprints,” “Social Jet Lag,” and Health

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