The long-held belief that adults need exactly eight hours of sleep per night is being challenged by new research, which suggests that individual sleep requirements can differ significantly. A review published in the journal Brain Medicine questions the universality of the eight-hour sleep norm, highlighting that consolidated nocturnal sleep is not an evolutionary constant.
Historical and anthropological data indicate that human sleep patterns have varied considerably. Studies of pre-industrial societies, particularly hunter-gatherer communities with minimal exposure to artificial light, have revealed shorter average sleep durations. Research cited by The Conversation, for instance, found that individuals in Tanzania, Namibia, and Bolivia slept between 5.7 and 7.1 hours per night, often waking naturally near dawn without making up for lost sleep with daytime naps. An analysis published by Royal Society Publishing estimates that people in pre-industrial societies slept an average of 6.4 hours nightly.
This deviation from modern sleep norms is partly attributed to the widespread use of artificial light. Sources suggest that artificial light, from sources like lamps, computers, and smartphones, disrupts natural sleep cycles by altering the body's internal clock, which regulates wakefulness and sleep timing. Unlike ancestral patterns that often aligned with natural light-dark cycles, modern sleep is frequently delayed, with many individuals experiencing shorter sleep during the workweek and longer sleep on weekends.
Individual factors, including health status and biological sex, also play a crucial role in determining sleep needs. Some large-scale studies suggest that the optimal amount of sleep associated with the best health outcomes may be less than eight hours for many. One study using advanced imaging and molecular measures estimated an ideal sleep range of 6.4 to 7.8 hours, depending on individual characteristics.
The National Sleep Foundation generally recommends that adults aged 26 to 64 aim for seven to nine hours of sleep per night, acknowledging that some individuals may function well with six to ten hours. Ultimately, the concept of a single “sweet spot” for sleep appears to be an oversimplification, with personal requirements being the most significant factor.