The long-standing belief that every adult needs exactly eight hours of sleep each night is increasingly being questioned by sleep scientists and evolutionary researchers. Harvard evolutionary biologist Daniel E. Lieberman argues that the eight-hour rule is more a cultural myth rooted in the Industrial Era than a biological necessity. Studies show that in pre-industrial societies, where electricity was absent, people generally slept between six and seven hours without daytime naps, challenging modern sleep prescriptions.
Large-scale health datasets reveal a U-shaped curve regarding sleep duration and health risks. Sleep lasting about seven hours is consistently linked to the lowest rates of mortality and cardiovascular issues, while both shorter and longer sleep durations carry increased health risks. This U-shaped relationship has been supported by multiple studies, including extensive analyses from the U.K. Biobank. These findings suggest that seven hours of sleep often outperforms the traditional eight-hour target for many healthy adults.
Recommendations from authoritative bodies like the American Academy of Sleep Medicine and the Sleep Research Society emphasize that adults should aim for seven or more hours of sleep per night, focusing on a range rather than a fixed number. The Mayo Clinic aligns with this guideline, noting that individual sleep needs vary based on factors like age, quality of sleep, previous sleep deficits, pregnancy, and natural changes in sleep patterns with aging.
Practically, adults should strive for consistency in sleep schedules and prioritize sleep quality over strict hour counts. Measures such as maintaining regular bedtimes and wake times, exposing oneself to morning light, minimizing nighttime blue light exposure, and creating a cool, dark sleeping environment contribute significantly to restorative sleep. Avoiding excessive caffeine and alcohol close to bedtime also supports better sleep hygiene.
If an individual consistently requires more than nine hours of sleep, this may be indicative of underlying health issues such as depression, sleep apnea, or other chronic conditions and should prompt a consultation with a healthcare provider.
Ultimately, the “eight-hour sleep” rule is an oversimplification that doesn’t fit everyone’s biological needs. For many adults, seven hours of sleep hits a healthful sweet spot, with some needing slightly more or less depending on their lifestyle and health status. Shifting the focus toward sleep quality and daytime functioning can help business leaders and individuals prioritize habits that promote long-term health and performance.
