The question of the ideal amount of sleep for an adult was historically answered unequivocally: eight hours per day. This concept emerged in the mid-19th century when the division of eight hours for work, eight for leisure, and eight for rest was established.
However, recent evidence suggests that eight hours may not be the most suitable sleep period for everyone. A new narrative review published in the scientific journal Brain Medicine points to this possibility.
Researchers investigated hunter-gatherer communities whose lifestyles are more similar to those of their ancestors and who have little or no exposure to artificial light. In a preliminary study, it was found that individuals in Tanzania, Namibia, and Bolivia slept between 5.7 and 7.1 hours per night. These short periods were not attributed to traffic noise, social media use, or excessive nighttime illumination.
Additionally, these people appeared to have sufficient sleep, as they did not compensate with long daytime naps, waking naturally near sunrise, regardless of the day of the week. Although the exact time varies according to measurement, location, season, and other environmental factors, a recent analysis estimated the average for these societies at 6.4 hours.
The studies are based on the premise that natural sleep reflects real need, implying that these hunter-gatherers would be free from the stress and pressures typical of modern societies. However, it is questioned whether these populations face the same health problems related to sleep deprivation observed today, which weakens the argument against eight hours.
Other research, stemming from large studies on the correlation between sleep and health in industrialized contexts, has brought new information. If ideal sleep is defined as that associated with the best health condition, various studies indicate that the optimal point may be less than eight hours. A recent study, using brain and body imaging and molecular analyses, evaluated the link between sleep and organ aging, estimating that the ideal amount would be between 6.4 and 7.8 hours, varying by sex and organ examined.
Many findings demonstrate that both sleeping too little and sleeping too much are linked to a more fragile state of health, including obesity, heart disease, and stroke, in addition to cognitive decline. However, scientists still debate whether excessive sleep is a cause or an early symptom of these health problems. Regardless, these discoveries challenge the idea that everyone needs exactly eight hours and suggest that consistently sleeping longer deserves consideration.