Imagine a 34-year-old person who presents a news broadcast transmitted in the early hours. To manage the routine, they sleep around 5 pm, wake up near midnight, train, work until dawn and only then have contact with daylight.
Over recent months, this type of inverted routine has become a frequent topic on social media: people who sleep in two blocks, people who swap day for night because of work and the increasingly repeated idea that "sleeping 8 hours straight" would simply be a modern invention, without scientific basis. Let's separate what is evidence from what is exaggeration.
Split sleep in two blocks is real, but it's not what's circulating
Before electric light, much of humanity appears to have slept in two periods per night: a "first sleep", soon after dark, an awake interval in the middle of the night and a "second sleep" until dawn. This description comes from more than two decades of historical research, based on letters, diaries and judicial records from different eras and continents, including reports about Brazilian indigenous peoples observed by a European traveller as far back as the sixteenth century.
The important point, which tends to get lost on social media, is that this split sleep added up to a total similar to what is recommended today. The difference was not in the number of hours, it was in the format: two parts, with a pause in between, rather than a single block.
The viral text has a problem: the mattress fraud didn't happen
A version that circulated quite recently claims that this split sleep pattern was abandoned because of research commissioned by a mattress factory, in the 1930s, to push the idea of single 8-hour sleep and sell more products. The text even credits Mozart with composing works during this nocturnal interval.
Independent fact-checks found no evidence of this fraud. The shift from split sleep to single sleep happened gradually, throughout the Industrial Revolution and the arrival of electric light, when it became possible to extend the day and fixed factory shifts began to require standardised hours. The scientist cited in the viral story is recognised for important contributions to sleep research, but there is no record of them having committed fraud at the request of any industry. And Mozart's own correspondence shows an irregular routine, including reports of having woken up in the middle of the night to compose, which contradicts the story of the "sacred interval".
In other words: split sleep existed, but the conspiracy explanation for its end doesn't hold up.
And sleeping at a time different from the conventional, as in the case at the beginning of the text?
Here it's worth distinguishing three situations that tend to be treated as if they were the same thing:
- Night chronotype with good routine: people who prefer to sleep and wake up later, and who can maintain adequate duration and regularity in a controlled environment (dark, quiet), have, by current evidence, no reason to force a more "conventional" schedule.
- Shift work with forced deprivation: when the sleep schedule is imposed by night-time work and conflicts with daylight and social life, there is real and well-documented risk of cardiovascular, metabolic, immunological and mental health problems. The mechanism is not "sleeping during the day is bad", it's the difficulty of maintaining sufficient and good quality sleep when the internal biological clock is in conflict with the environment.
- "Optimised" polyphasic sleep (several short naps totalling 2 to 4 hours per day): literature reviews found no proven benefit to this type of scheme, only harm to REM phase, cognition and metabolism. It is not recommended.
What really seems to matter, according to available evidence
- Sleep the total recommended for your age (generally 7 to 9 hours for adults).
- Maintain a relatively regular schedule, whether daytime or night-time.
- Have good quality sleep, without excessive fragmentation.
There is no fixed biological rule stating that sleep must necessarily happen at night. But swapping day for night by work requirement does, yes, have a health cost that deserves monitoring, and that's different from simply preferring to sleep later out of habit.
When it's worth seeking help
Sleeping at an unconventional time is not, in itself, a cause for concern, as long as the person wakes up rested and functions well throughout the day. It's time to seek medical evaluation when sleep comes with intense snoring or pauses in breathing, frequent urge to urinate at night, pain, anxiety when trying to sleep or excessive sleepiness during the period when they should be awake. In these cases, the sleep pattern may be being fragmented by a cause that needs to be treated, not because that's simply the person's natural way.
This content is for informational purposes and does not replace medical consultation. Each organism responds differently to changes in sleep routine, and persistent changes in sleep pattern deserve individual evaluation with a healthcare professional.