Imagine a 34-year-old person who presents a news broadcast transmitted in the early morning hours. To manage the routine, they sleep around 5 p.m., wake up near midnight, exercise, work until dawn, and only afterward have contact with daylight.

In recent months, this type of inverted routine has become a frequent topic on social media: people who sleep in two blocks, people who exchange day for night because of work, and the increasingly repeated idea that "sleeping 8 hours straight" would be just a modern invention with no scientific basis. Let's separate what is evidence from what is exaggeration.

Sleep divided into 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," shortly after nightfall, 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 traveler as early as the sixteenth century.

The important point, which tends to get lost on social media, is that this divided sleep added up to a total similar to what is recommended today. The difference was not in the number of hours, but in the format: two parts, with a pause in between, instead of a single block.

The viral text has a problem: the mattress fraud didn't happen

A version that circulated quite a bit recently claims that this pattern of divided sleep 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 nighttime interval.

Independent fact-checking has found no evidence of this fraud. The change from divided 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 standardized hours. The scientist cited in the viral story is recognized for important contributions to sleep research, but there is no record that they committed fraud at the behest 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."

That is: divided sleep did exist, but the conspiracy explanation for its end doesn't hold up.

And what about sleeping at a different time than the conventional one, 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:

  • Nocturnal chronotype with good routine: people who prefer to sleep and wake up later, and who manage to 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 sleep deprivation: when sleep time is imposed by night work and conflicts with daylight and social life, there is a 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, good-quality sleep when the internal biological clock is in conflict with the environment.
  • "Optimized" polyphasic sleep (several short naps totaling 2 to 4 hours per day): literature reviews have found no proven benefit to this type of schedule, only harm to REM sleep, 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 nighttime.
  • Have good quality sleep, without excessive fragmentation.

There is no fixed biological rule saying that sleep must necessarily happen at night. But switching day for night due to work demands does, in fact, 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 is accompanied by intense snoring or pauses in breathing, frequent urge to urinate at night, pain, anxiety when trying to sleep, or excessive daytime 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 this is simply the person's natural way.

This content is informational in nature and does not replace medical consultation. Each organism responds differently to changes in sleep routine, and persistent changes in sleep pattern merit individual evaluation with a healthcare professional.