Scientists: Not Everyone Needs To Sleep Eight Hours

A new study has turned our understanding of healthy sleep on its head.

Eight hours of sleep is not a biologically mandatory standard for every adult. A new review of scientific data shows that sleep needs vary from person to person, and that the quality and benefits of sleep are also influenced by regularity, bedtime, and alignment with the circadian rhythm.

This is discussed in a study published in the journal Brain Medicine.

Where Did the Eight-Hour Rule Come From?

Researchers analyzed data from anthropology, history, and comparative genomics to understand how people slept before the advent of electric lighting, smartphones, and modern work schedules. It turned out that human sleep has historically been much more flexible than the popular “eight hours every night” model suggests.

To this end, the scientists drew, in particular, on studies of traditional hunter-gatherer communities. Among people living without constant artificial lighting, sleep duration in various studies ranged from approximately 6.4 to 7.1 hours per day.

However, this does not mean that six hours is enough for all adults. The researchers themselves note that these data rather demonstrate that human sleep does not have a single fixed duration that suits everyone equally.

It’s not just the number of hours of sleep that matters

Modern life has significantly changed not only the duration but also the timing of sleep. Artificial light in the evening can delay falling asleep and affect the internal biological clock that regulates the sleep-wake cycle.

Another issue is the difference between workdays and weekends. People often sleep less during the week and then try to make up for the lack of sleep with longer rest on Saturday and Sunday. As a result, bedtime and wake-up times are constantly changing.

Therefore, the authors of the review suggest taking a broader view of sleep: evaluating not only the number of hours, but also the regularity, timing, and alignment with the circadian rhythm.

How Many Hours Do You Need?

Even the same amount of sleep can be experienced differently by different people. Sleep needs are influenced, in particular, by age, health status, and individual biological characteristics.

One of the studies discussed in this article used brain and body scans and molecular markers to investigate the link between sleep duration and the aging of various organs. For different organs and genders, the researchers determined a range of approximately 6.4–7.8 hours to be optimal for the biological age of the study participants.

However, this does not mean that this exact number of hours is a universal standard. By comparison, the Centers for Disease Control and Prevention (CDC) currently recommends that adults aged 18–60 get 7 or more hours of sleep, those aged 61–64 get 7–9 hours, and those 65 and older get 7–8 hours.

In other words, the new review does not overturn the recommendation to get enough sleep. Rather, it calls into question the idea that everyone must necessarily aim for exactly eight hours, regardless of their own needs.

Scientists Have Identified Different Types of Sleep

Another study mentioned in the review showed just how different people’s sleep can be. The researchers analyzed data from 770 healthy young adults and, using indicators of sleep, brain activity, memory, health, and lifestyle, identified five distinct sleep profiles.

Some participants generally had poor sleep, while others—on the contrary—did not report any problems, even though they had other psychological or social characteristics. Other profiles were linked to sleep duration, the use of sleep aids, sleep disorders, or cognitive measures.

This reinforces the main idea of the new study: sleep is not just about the number of hours.

Sleep regularity also affects health

An even larger analysis included 88,461 participants in the UK Biobank, who were followed for an average of about 6.8 years. The researchers examined not only sleep duration but also the time it took to fall asleep, the regularity of the circadian rhythm, sleep efficiency, and nighttime awakenings.

As a result, they found associations between various sleep characteristics and 172 diseases. Notably, a significant portion of these associations was linked not to the number of hours slept, but to other sleep characteristics, particularly sleep rhythm and regularity.

At the same time, this study does not prove that irregular sleep directly causes these diseases. The authors themselves note the study’s limitations, specifically that the participants were predominantly middle-aged and older adults.

So how much sleep do you need?

The main conclusion of the new review is not that we should forget the “eight-hour rule” or that six hours of sleep is enough for everyone. The point is something else: eight hours is a guideline, not a universal biological constant.

For one person, about seven hours may be comfortable, while another may need closer to nine. It’s also important whether a person wakes up feeling rested, whether they wake up multiple times during the night, and whether they feel constantly sleepy during the day.

So the modern view of healthy sleep is gradually moving away from simple arithmetic. The number of hours remains important, but regularity, the time of sleep, and its uninterrupted nature can be just as significant.

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