Sleep Optimization

Sleep optimization refers to achieving both adequate sleep duration and good sleep quality, which together constitute a cardinal component of a healthy lifestyle at the basis of preventing many non-communicable chronic diseases. ^[1] A National Sleep Foundation expert panel agreed that sleep continuity measures including sleep latency, number of awakenings longer than 5 minutes, wake after sleep onset, and sleep efficiency are appropriate indicators of good sleep quality across the life-span. ^[2] Sleep quality may be a more meaningful measure of sleep than absolute duration, and sleep duration and executive function display a quadratic relationship suggesting an optimal amount of sleep is required for daily cognitive processes. ^[3]

Sleep and immunity are bidirectionally linked, and in the absence of an infectious challenge sleep appears to promote inflammatory homeostasis through effects on inflammatory mediators such as cytokines. ^[4] The glymphatic system, which clears the brain of protein waste products, is mostly active during sleep and degrades with age, suggesting a causal relationship between sleep disturbance and progression in neurodegenerative dementias. ^[5] Reduced sleep duration is related to an increased risk of obesity, potentially through imbalance of appetite regulation involving hormones such as orexin, ghrelin, leptin, and insulin. ^[6]

A systematic review and meta-analysis of 16 prospective studies with 1,382,999 participants and 112,566 deaths found short sleep duration associated with a relative risk of death of 1.12 and long sleep duration with a relative risk of 1.30. ^[7] A meta-analysis of 72 studies with more than 50,000 participants found that sleep disturbance and long sleep duration, but not short sleep duration, were associated with increases in markers of systemic inflammation such as C-reactive protein and interleukin-6. ^[8] A systematic review of 41 studies including 92,340 participants found that later sleep timing and greater variability in sleep were both associated with adverse health outcomes, while weekend catch-up sleep was associated with better health outcomes. ^[9] A meta-analysis of 23 randomized controlled trials found that exogenous melatonin significantly improved sleep quality as assessed by the Pittsburgh Sleep Quality Index, with a weighted mean difference of -1.24. ^[10] A network meta-analysis of 35 trials involving 3519 older adults found that exercise, including muscle endurance training combined with walking, Tai chi, and resistance training

Sleep has a critical role in promoting health, with sleep disturbance exerting a powerful influence on the risk of infectious disease and on the occurrence and progression of major medical illnesses including cardiovascular disease, cancer, and depression. ^[12] Sleep is an important modifiable lifestyle factor to improve daily cognition and possibly reduce the risk of developing dementia, with poor sleep efficiency and sleep fragmentation linked to poorer executive function and increased dementia risk. ^[3] The American Heart Association added sleep health as a new component of its Life's Essential 8 construct of cardiovascular health, alongside diet, physical activity, and other established metrics. ^[13]