While 7 hours may meet the minimum requirement for many adults, research increasingly supports the idea that approximately 8 to 9 hours — averaging around 8.5 hours — may provide the most complete health benefits for long-term wellness and performance.

7 hours not good enough

Large-scale scientific consensus indicates that seven hours of sleep represents the lower threshold for healthy adult sleep duration. A joint statement from the American Academy of Sleep Medicine and the Sleep Research Society concluded that adults should obtain seven or more hours of sleep nightly to maintain good health. Chronic sleep shorter than seven hours has been associated with obesity, diabetes, cardiovascular disease, depression, weakened immunity, and increased mortality risk. These findings demonstrate that consistently sleeping below seven hours can compromise multiple biological systems and increase long-term disease risk.

Sleep to heal

However, while seven hours may prevent sleep deficiency, it does not necessarily represent optimal sleep duration. Public health and epidemiological studies commonly place adult sleep recommendations at 8.5 hours per night, acknowledging that many individuals function best toward the upper end of this range. Within this range, several studies suggest that sleep closer to 8 or 9 hours is linked with improved cognitive performance, emotional stability, and physical recovery.

Research examining long-term health outcomes further supports this view. Population studies examining successful ageing and overall health often show a “U-shaped” relationship between sleep duration and health outcomes. Both short and excessively long sleep are linked to poorer health (though long sleep may just be a symptom of poor quality sleep), while moderate durations tend to produce the best results. For example, studies examining ageing populations have found that individuals who consistently sleep roughly 7 to 8 hours experience higher rates of healthy ageing, including better physical function, mental health, and cognitive performance.

In addition, sleep science increasingly emphasizes that sleep is not just about avoiding deficiency but achieving full biological restoration. During deeper sleep stages, the brain consolidates memories, regulates hormones, and clears metabolic waste. Achieving sufficient time in both deep and rapid-eye-movement (REM) sleep often requires more than the bare minimum threshold. Since sleep cycles typically last about 90 minutes, completing five full cycles — which totals roughly 7.5 hours — may still leave some individuals slightly short of optimal restoration. Extending rest toward six complete cycles, or approximately 8 to 9 hours, may allow the body to complete additional restorative processes.

Sleep to keep the demons away

Sleep duration is also closely linked with mental health. Longitudinal research tracking sleep patterns has found that individuals who maintain recommended sleep durations are significantly less likely to develop depression or anxiety disorders compared to those who regularly fall outside these ranges. Adequate sleep supports emotional regulation, stress management, and cognitive resilience, all of which improve with slightly longer and more consistent sleep duration.

Sleep 8.5 hours each night

Reading between the lines, we conclude that 7 hours is not enough. Especially if your days are physically intensive, and thus need more rest for muscle repair.

The optimal target for most adults appears closer to 8.5 hours per night. This duration allows individuals to fully complete sleep cycles, enhance physiological recovery, and maximise long-term health benefits.

Scientific Sources

• Watson NF, et al. Recommended Amount of Sleep for a Healthy Adult: A Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society. 2015.
• Hirshkowitz M, et al. National Sleep Foundation Sleep Time Duration Recommendations. Sleep Health. 2015.
• Scott H, et al. Research on recommended 7–9 hours sleep duration and health outcomes.
• Windred DP, et al. Association of Sleep Regularity with Depression and Anxiety. Psychological Medicine.