8-hour sleep rule is old and ‘too simple’, research says. Find out how much sleep do humans actually need

For years, eight hours of sleep has been treated almost like a fixed rule for adults. But sleep researchers say there is no single number that works for everyone. A new review published in Brain Medicine suggests that the familiar eight-hour target is too simple, with sleep needs varying from one person to another.

The research also points to another part of sleep that often gets ignored. It is not only about how many hours you sleep, but also when you sleep and how regular your schedule is.

Where did the 8-hour sleep rule come from?

The idea of eight hours did not come from a biological rule that applies to every adult. The concept became popular in the 19th century alongside the idea of dividing the day into eight hours each for work, recreation and sleep.


But researchers looking at sleep patterns in societies with little exposure to modern artificial light have found that people do not always naturally sleep for eight hours.

The Brain Medicine review notes, “Human sleep patterns in pre-industrial societies exhibit substantial flexibility, suggesting that contemporary norms of consolidated nocturnal sleep are not evolutionarily fixed.”

One study published in Current Biology looked at communities in Tanzania, Namibia and Bolivia and found that people slept between 5.7 and 7.1 hours a night. They generally did not compensate for those shorter nights by taking long daytime naps.

As reported by The Conversation, “The short nights also seemed to be enough: People did not make up for them with long daytime naps. Without an alarm clock, they tended to wake close to dawn, regardless of the day of the week.”

Another analysis published by the Royal Society estimated that people in preindustrial societies slept around 6.4 hours per night.

Your body may need a different amount

These findings do not mean that everyone should suddenly start sleeping for six hours. Researchers also point out that natural sleep duration is affected by several factors, and people living in traditional societies may not necessarily represent a perfect picture of how much sleep humans need for good health.

Research involving modern populations also suggests that the ideal amount is not necessarily eight hours.

A study published in Nature examined brain and body scans along with molecular measurements to study the relationship between sleep and the ageing of organs. It estimated that the optimal sleep duration could range from 6.4 to 7.8 hours, depending on factors including a person's sex and the organ being studied.

Large studies have also found links between both insufficient and excessive sleep and poorer health. However, researchers are still trying to determine whether very long sleep contributes to these health problems or can sometimes be an early sign of an existing problem.

When you sleep matters too

The timing of sleep can be just as important as the total number of hours. Artificial lighting from lamps, computers and smartphones has changed modern sleeping habits and can push the body's internal clock later.

The Brain Medicine review states, “Industrialisation, electrification, and urbanisation have profoundly altered human sleep timing, duration, and regularity, primarily through disruption of natural light-dark cycles.”

It also warns, “Modern societal factors, including artificial illumination and night shift work, contribute to chronic circadian misalignment with measurable consequences for physiological and mental health.”

People also commonly sleep less during the working week and try to catch up on weekends. While maintaining a regular sleep schedule is generally better, getting some additional sleep after a period of short sleep can still be useful.

So, how much sleep do you actually need?

There is no need to force yourself to hit exactly eight hours every night. The National Sleep Foundation recommends seven to nine hours for adults aged 26 to 64, while noting that six to 10 hours may be appropriate for some adults.

As The Conversation puts it, “The eight-hour rule is clearly too simple. People need different amounts of sleep, and when we sleep matters too.”

The bigger takeaway is simple: eight hours is a useful general benchmark, but it is not a biological deadline. Your age, health, lifestyle and individual sleep needs all matter, and an occasional bad night's sleep does not mean something is necessarily wrong.