Sleep is often positioned as essential for health, with 7-8 hours commonly recommended for adults. But research suggests that while sleep is critical,
the exact amount each person needs can vary, and the idea of a fixed ‘eight-hour rule’ may be too simplistic.
Research shows that chronic sleep deprivation is associated with a range of health risks. One explanation lies in the brain’s glymphatic system — a waste-clearance mechanism that becomes active during sleep and helps remove misfolded proteins such as beta-amyloids, which are found in people with Alzheimer’s disease. Poor sleep, particularly in midlife, has been identified as a risk factor for cognitive decline later in life.
Beyond the brain, insufficient sleep is linked to increased risks of cardiovascular disease, stroke, and disruptions across multiple physiological systems, including immune and respiratory function. Sleep also affects how the brain processes pain and emotional experiences, making individuals more vulnerable to both.
At the same time, sleep needs are not uniform. Research from Harvard Medical School suggests that while most healthy adults are advised to get at least seven hours of sleep, some people may naturally require less, while others may need more.
Rather than focusing only on duration, experts emphasise sleep quality and daytime functioning. According to sleep specialist Eric Zhou, writing for Harvard Health Publishing, feeling refreshed on waking and having enough energy to get through the day are more useful indicators of adequate sleep than hitting a specific number of hours.
Sleep quality includes factors such as whether a person sleeps through the night, how often they wake up, and how long it takes to fall asleep. Poor sleep quality has been associated with higher risks of conditions, including heart disease, stroke, diabetes, and mental health issues such as anxiety and depression, according to Harvard Health Publishing.
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Sleep patterns can also change over time. As people age, natural shifts in the body’s circadian rhythm and a gradual decline in melatonin production can lead to lighter, more fragmented sleep and earlier wake times.
At a biological level, newer research from the University of Oxford offers insight into why sleep is necessary in the first place. A study published in Nature found that the pressure to sleep may arise from a build-up of electrical stress in mitochondria (the structures inside cells that generate energy). When this stress increases, it can trigger signals that push the brain into sleep, helping restore balance and prevent cellular damage.
The findings suggest that sleep is not just rest, but a process tied to how the body manages energy at a cellular level.
Short-term sleep loss, however, is not necessarily harmful. Occasional poor sleep may affect mood, focus and alertness, but the body has the capacity to compensate for it. Over time, though, consistently disrupted or insufficient sleep may have broader health consequences.
Catch-up sleep can help offset sleep loss to some extent, but irregular sleep patterns — such as significantly changing sleep and wake times — may disrupt the body’s internal clock.
Sleep time, then, is essential, but not one-size-fits-all. While general recommendations suggest 7-8 hours, research indicates that individual needs vary, and both sleep duration and quality play a role.
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