Background: Previous observational epidemiological studies have reported inconsistent findings about the association between longer durations of sleep and the risk of cognitive impairment and dementia. To investigate the association between longer durations of sleep and the risk of cognitive decline, we performed a meta-analysis of observational studies. Methods: We searched PubMed, EMBASE, and the bibliographies of relevant articles to retrieve additional studies in July 2015. A total of 53,942 participants (mean age 66.9 years) were included in the final analysis. Three evaluators independently reviewed and selected articles, based on pre-determined selection criteria. Results: Among a total of 695 articles, 10 observational epidemiological studies with 3 case-control studies and 7 cohort studies were included in the final analysis. Compared to the average sleep duration, the odds ratio or relative risk of the longest sleep duration was 1.42 (95% CI 1.27-1.59) for cognitive decline in the fixed-effect meta-analysis, 1.38 for cognitive impairment (95% CI 1.23-1.56), and 1.42 for dementia (95% CI 1.15-1.77). Subgroup meta-analyses by various factors such as study design, type of cognitive decline, gender, region, age, and methodological quality of study showed consistent findings. Conclusion: The current meta-analysis found that longer duration of sleep is associated with an increased risk of cognitive decline.

Liu Y, Wheaton AG, Chapman DP, Croft JB: Sleep duration and chronic diseases among U.S. adults age 45 years and older: evidence from the 2010 behavioral risk factor surveillance system. Sleep 2013;36:1421-1427.
Ikehara S, Iso H, Date C, Kikuchi S, Watanabe Y, Wada Y, Inaba Y, Tamakoshi A: Association of sleep duration with mortality from cardiovascular disease and other causes for Japanese men and women: the JACC study. Sleep 2009;32:295-301.
Vgontzas AN, Liao D, Pejovic S, Calhoun S, Karataraki M, Bixler EO: Insomnia with objective short sleep duration is associated with type 2 diabetes: a population-based study. Diabetes Care 2009;32:1980-1985.
Vgontzas AN, Liao D, Bixler EO, Chrousos GP, Vela-Bueno A: Insomnia with objective short sleep duration is associated with a high risk for hypertension. Sleep 2009;32:491-497.
Leng Y, Cappuccio FP, Wainwright NW, Surtees PG, Luben R, Brayne C, Khaw KT: Sleep duration and risk of fatal and nonfatal stroke: a prospective study and meta-analysis. Neurology 2015;84:1072-1079.
Merlino G, Piani A, Gigli GL, Cancelli I, Rinaldi A, Baroselli A, Serafini A, Zanchettin B, Valente M: Daytime sleepiness is associated with dementia and cognitive decline in older Italian adults: a population-based study. Sleep Med 2010;11:372-377.
Foley D, Monjan A, Masaki K, Ross W, Havlik R, White L, Launer L: Daytime sleepiness is associated with 3-year incident dementia and cognitive decline in older Japanese-American men. J Am Geriatr Soc 2001;49:1628-1632.
Schmutte T, Harris S, Levin R, Zweig R, Katz M, Lipton R: The relation between cognitive functioning and self-reported sleep complaints in nondemented older adults: results from the Bronx aging study. Behav Sleep Med 2007;5:39-56.
Blackwell T, Yaffe K, Ancoli-Israel S, Redline S, Ensrud KE, Stefanick ML, Laffan A, Stone KL: Association of sleep characteristics and cognition in older community-dwelling men: the MrOS sleep study. Sleep 2011;34:1347-1356.
Faubel R, Lopez-Garcia E, Guallar-Castillon P, Graciani A, Banegas JR, Rodríguez-Artalejo F: Usual sleep duration and cognitive function in older adults in Spain. J Sleep Res 2009;18:427-435.
Ramos AR, Dong C, Elkind MS, Boden-Albala B, Sacco RL, Rundek T, Wright CB: Association between sleep duration and the mini-mental score: the Northern Manhattan study. J Clin Sleep Med 2013;9:669-673.
Tworoger SS, Lee S, Schernhammer ES, Grodstein F: The association of self-reported sleep duration, difficulty sleeping, and snoring with cognitive function in older women. Alzheimer Dis Assoc Disord 2006;20:41-48.
Blackwell T, Yaffe K, Ancoli-Israel S, Schneider JL, Cauley JA, Hillier TA, Fink HA, Stone KL: Poor sleep is associated with impaired cognitive function in older women: the study of osteoporotic fractures. J Gerontol A Biol Sci Med Sci 2006;61:405-410.
Potvin O, Lorrain D, Forget H, Dubé M, Grenier S, Préville M, Hudon C: Sleep quality and 1-year incident cognitive impairment in community-dwelling older adults. Sleep 2012;35:491-499.
Ferrie JE, Shipley MJ, Akbaraly TN, Marmot MG, Kivimäki M, Singh-Manoux A: Change in sleep duration and cognitive function: findings from the Whitehall II study. Sleep 2011;34:565-573.
Devore EE, Grodstein F, Duffy JF, Stampfer MJ, Czeisler CA, Schernhammer ES: Sleep duration in midlife and later life in relation to cognition. J Am Geriatr Soc 2014;62:1073-1081.
Hahn EA, Wang HX, Andel R, Fratiglioni L: A change in sleep pattern may predict Alzheimer disease. Am J Geriatr Psychiatry 2014;22:1262-1271.
Wells GA, Shea B, O'Connell D: The Newcastle-Ottawa Scale (NOS) for Assessing the Quality of Nonrandomised Studies in Meta-Analyses.
Higgins JP, Thompson SG: Quantifying heterogeneity in a meta-analysis. Stat Med 2002;21:1539-1558.
DerSimonian R, Laird N: Meta-analysis in clinical trials. Control Clin Trials 1986;7:177-188.
Yaffe K, Laffan AM, Harrison SL, Redline S, Spira AP, Ensrud KE, Ancoli-Israel S, Stone KL: Sleep-disordered breathing, hypoxia, and risk of mild cognitive impairment and dementia in older women. JAMA 2011;306:613-619.
Cross N, Terpening Z, Rogers NL, Duffy SL, Hickie IB, Lewis SJ, Naismith SL: Napping in older people “at risk” of dementia: relationships with depression, cognition, medical burden and sleep quality. J Sleep Res 2015;24:494-502.
Blackwell T, Yaffe K, Laffan A, Redline S, Ancoli-Israel S, Ensrud KE, Song Y, Stone KL: Associations between sleep-disordered breathing, nocturnal hypoxemia, and subsequent cognitive decline in older community-dwelling men: the Osteoporotic Fractures in Men Sleep Study. J Am Geriatr Soc 2015;63:453-461.
Kronholm E, Sallinen M, Suutama T, Sulkava R, Era P, Partonen T: Self-reported sleep duration and cognitive functioning in the general population. J Sleep Res 2009;18:436-446.
Saint Martin M, Sforza E, Barthélémy JC, Thomas-Anterion C, Roche F: Does subjective sleep affect cognitive function in healthy elderly subjects? The Proof cohort. Sleep Med 2012;13:1146-1152.
Spira AP, Gamaldo AA, An Y, Wu MN, Simonsick EM, Bilgel M, Zhou Y, Wong DF, Ferrucci L, Resnick SM: Self-reported sleep and β-amyloid deposition in community-dwelling older adults. JAMA Neurol 2013;70:1537-1543.
Auyeung TW, Lee JS, Leung J, Kwok T, Leung PC, Woo J, Wing YK: Cognitive deficit is associated with phase advance of sleep-wake rhythm, daily napping, and prolonged sleep duration - a cross-sectional study in 2,947 community-dwelling older adults. Age (Dordr) 2013;35:479-486.
Lo JC, Loh KK, Zheng H, Sim SK, Chee MW: Sleep duration and age-related changes in brain structure and cognitive performance. Sleep 2014;37:1171-1178.
Miller MA, Wright H, Ji C, Cappuccio FP: Cross-sectional study of sleep quantity and quality and amnestic and non-amnestic cognitive function in an ageing population: the English Longitudinal Study of Ageing (ELSA). PLoS One 2014;26:e100991.
Gildner TE, Liebert MA, Kowal P, Chatterji S, Snodgrass JJ: Associations between sleep duration, sleep quality, and cognitive test performance among older adults from six middle income countries: results from the Study on Global Ageing and Adult Health (SAGE). J Clin Sleep Med 2014;10:613-621.
Stewart CA, Auger RR, Enders FT, Felmlee-Devine D, Smith GE: The effects of poor sleep quality on cognitive function of patients with cirrhosis. J Clin Sleep Med 2014;10:21-26.
Fetveit A, Bjorvatn B: Sleep duration during the 24-hour day is associated with the severity of dementia in nursing home patients. Int J Geriatr Psychiatry 2006;21:945-950.
Benito-León J, Louis ED, Villarejo-Galende A, Romero JP, Bermejo-Pareja F: Long sleep duration in elders without dementia increases risk of dementia mortality (NEDICES). Neurology 2014;83:1530-1537.
Sales LV, Bruin VM, D'Almeida V, Pompéia S, Bueno OF, Tufik S, Bittencourt L: Cognition and biomarkers of oxidative stress in obstructive sleep apnea. Clinics (Sao Paulo) 2013;68:449-455.
Xu L, Jiang CQ, Lam TH, Liu B, Jin YL, Zhu T, Zhang WS, Cheng KK, Thomas GN: Short or long sleep duration is associated with memory impairment in older Chinese: the Guangzhou Biobank Cohort Study. Sleep 2011;34:575-580.
Benito-León J, Bermejo-Pareja F, Vega S, Louis ED: Total daily sleep duration and the risk of dementia: a prospective population-based study. Eur J Neurol 2009;16:990-997.
Loerbroks A, Debling D, Amelang M, Stürmer T: Nocturnal sleep duration and cognitive impairment in a population-based study of older adults. Int J Geriatr Psychiatry 2010;25:100-109.
Keage HA, Banks S, Yang KL, Morgan K, Brayne C, Matthews FE: What sleep characteristics predict cognitive decline in the elderly? Sleep Med 2012;13:886-892.
Virta JJ, Heikkilä K, Perola M, Koskenvuo M, Räihä I, Rinne JO, Kaprio J: Midlife sleep characteristics associated with late life cognitive function. Sleep 2013;36:1533-1541.
Blackwell T, Yaffe K, Laffan A, Ancoli-Israel S, Redline S, Ensrud KE, Song Y, Stone KL: Associations of objectively and subjectively measured sleep quality with subsequent cognitive decline in older community-dwelling men: the MrOS sleep study. Sleep 2014;37:655-663.
Benito-León J, Louis ED, Bermejo-Pareja F. Cognitive decline in short and long sleepers: a prospective population-based study (NEDICES). J Psychiar Res 2013;47:1998-2003.
Chen JC, Espeland MA, Brunner RL, Lovato LC, Wallace RB, Leng X, Phillips LS, Robinson JG, Kotchen JM, Johnson KC, Manson JE, Stefanick ML, Sarto GE, Mysiw WJ: Sleep duration, cognitive decline, and dementia risk in older women. Alzheimers Dement 2016;2:21-33.
Spira AP, Blackwell T, Stone KL, Redline S, Cauley JA, Ancoli-Israel S, Yaffe K: Sleep-disordered breathing and cognition in older women. J Am Geriatr Soc 2008;56:45-50.
Patel SR, Zhu X, Storfer-Isser A, Mehra R, Jenny NS, Tracy R, Redline S: Sleep duration and biomarkers of inflammation. Sleep 2009;32:200-204.
Grandner MA, Buxton OM, Jackson N, Sands-Lincoln M, Pandey A, Jean-Louis G: Extreme sleep durations and increased C-reactive protein: effects of sex and ethnoracial group. Sleep 2013;36:769-779E.
Azizi G, Navabi SS, Al-Shukaili A, Seyedzadeh MH, Yazdani R, Mirshafiey A: The role of inflammatory mediators in the pathogenesis of Alzheimer's disease. Sultan Qaboos Univ Med J 2015;15:e305-e316.
Orsini F, De Blasio D, Zangari R, Zanier ER, De Simoni MG: Versatility of the complement system in neuroinflammation, neurodegeneration and brain homeostasis. Front Cell Neurosci 2014;8:380.
Blach-Olszewska Z, Leszek J: Mechanisms of over-activated innate immune system regulation in autoimmune and neurodegenerative disorders. Neuropsychiatr Dis Treat 2007;3:365-372.
Akiyama H, Barger S, Barnum S, Bradt B, Bauer J, Cole GM, Cooper NR, Eikelenboom P, Emmerling M, Fiebich BL, Finch CE, Frautschy S, Griffin WS, Hampel H, Hull M, Landreth G, Lue L, Mrak R, Mackenzie IR, McGeer PL, O'Banion MK, Pachter J, Pasinetti G, Plata-Salaman C, Rogers J, Rydel R, Shen Y, Streit W, Strohmeyer R, Tooyoma I, Van Muiswinkel FL, Veerhuis R, Walker D, Webster S, Wegrzyniak B, Wenk G, Wyss-Coray T: Inflammation and Alzheimer's disease. Neurobiol Aging 2000;21:383-421.
Kronholm E, Sallinen M, Era P, Suutama T, Sulkava R, Partonen T: Psychomotor slowness is associated with self-reported sleep duration among the general population. J Sleep Res 2011;20:288-297.
Lavie P: Self-reported sleep duration - what does it mean? J Sleep Res 2009;18:385-386.
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