Table 1.

Table displaying the design, sample characteristics, results, and exclusion criteria of the studies in the review.

Author, Year Country	Design	Sample Characteristics	Results	Exclusion Criteria/Statistical Adjustment
Ramos et al., (2013) [11] USA	Cross-Sectional	N—927 Mean Age—75 % Female—61	TST: Long sleep (≥9 h) inversely associated with MMSE score and short sleep (<6 h) not associated with MMSE score.	Statistical: Demographics, vascular factors, medications, risk for SDB, depression, alcohol consumption
Blackwell et al., (2006) [12] USA	Cross-Sectional	N—2932 Age—83.5 (±3.7) % Female—100	SL: Longer SL was significantly associated with worse global cognition, attention, and executive function. WASO: Longer WASO was significantly associated with worse global cognition, attention, and executive function. SE: Lower SE was significantly associated with worse global cognition, attention, and executive function. TST: TST was significant associated with worse global cognition but was not associated with executive function or attention.	Statistical: Age, race, depression, education, BMI, health status, Hx. of stroke, Hx. of hypertension, IADL impairments, smoking, alcohol use, caffeine intake, antidepressant use, physical activity
Blackwell et al., (2011) [13] USA	Cross-Sectional	N—3132 Mean Age—76.4 % Female—0	WASO: Longer objective WASO was associated with poorer global cognition, attention, and executive function. SE: Lower objective SE modeled continuously was associated with poorer attention and executive functioning but not global cognition. TST: Objective long sleep duration was associated with global cognitive functioning but not attention and executive function. Objective short sleep was not associated with global cognition, attention, or EF. Subjective short sleep (<5 h) and long sleep (>8 h) duration were associated with lower levels of global cognition. Long sleep, not short, was associated with poorer attention and executive function. The association between long sleep and global cognition, attention, and executive function disappeared after adjustment with WASO. General Sleep Problems: PSQI (>5) was not associated with global cognitive function, attention, or executive function.	Statistical: Age, race, clinic, education, depression, BMI, number of IADLs, comorbidities, antidepressant use, benzodiazepine use, alcohol use, smoking, physical activity, self-reported health status
Devore et al., (2014) [14] USA	Prospective	N—15,263 Mean Age—74.2 % Female—100	TST: Short ≤5 h and long ≥9 h were associated with worse verbal fluency, working and episodic memory and global cognition score than those with 7 h sleep. An increase or decrease in sleep duration was associated with worse verbal fluency, working and episodic memory and global cognition scores. No association was found between sleep duration and cognitive decline.	Statistical: Age, education, shift-work history, smoking status, alcohol intake, physical activity, body mass index, history of high blood pressure, medical outcomes study mental health score, living alone, tranquilizer use
Tworoger et al., (2006) [15] USA	Cross-Sectional Longitudinal (2 years)	N—1844 Mean age—74.1 % Female—100	TST: Cross sectionally, short sleep (≤5 h) but not long sleep (≥9 h) duration was associated with an increased risk of global cognitive impairment, and verbal fluency but not episodic memory. Longitudinally (2 years), neither short nor long sleep duration was associated with global cognition, episodic memory, or verbal fluency. General Sleep Problems: Cross-sectionally but not longitudinally, persons who had regular difficulties falling or staying were at an increased risk for poorer global cognitive impairment compared to those with occasional or rare sleep difficulties. There were no cross-sectional or longitudinal associations between sleep difficulties and episodic memory or verbal fluency.	Exclusion Criteria: Taking antidepressants, physician-diagnosis of depression, diagnosis of stroke Statistics: Age, education, smoking status, physical activity, HTN, living status, alcohol consumption, mental health index, use of tranquilizers
Lambaise et al., (2014) [16] USA	Cross-sectional	N—121 Mean Age—73.3 % Female—100	SE: Lower objective SE was associated with poorer attention, executive function, and processing speed but not verbal fluency. Subjective SE not associated with attention, executive function, processing speed and verbal fluency. TST: Subjective shorter sleep time was associated with better executive function. Subjective and objective TST were not associated with attention, executive function, processing speed and verbal fluency.	Statistical: Education, race, BMI, depressive symptoms, height, weight, medication use, current hypertension, sleep medication use
Schmutte et al., (2007) [17] USA	Cross-Sectional	N—375 Mean Age—79.6 % Female—64.3	SL: Persons with longer SL performed significantly worse on measures of attention, working memory, verbal fluency, and processing speed. SL was not associated with episodic memory. After statistical adjustment, longer SL was associated with only verbal fluency. TST: In univariate analyses, short sleep (<6 h) and long sleep (>9 h) duration were not associated with episodic memory, attention, working memory, verbal fluency, or processing speed. ANCOVA analyses for episodic memory indicate an association with longer sleep duration (>9 h).	Statistical: Depression, age, education, medical comorbidities, physical morbidity, hypnotic use
St. Martin et al., (2012) [18] France	Cross-Sectional	N—272 Mean Age—74.8 % Female—71	SL: SL was not associated with any of the 7 cognitive function measures. TST: TST was not associated with any of the 7 cognitive function measures. General Sleep Problems: Higher PSQI total scores were correlated with a poorer global cognitive function, shorter working memory, and worse attention span. Poorer sleep quality associated with shorter working memory and poorer delayed episodic memory.	Exclusion Criteria: MI, heart failure, stroke, previous dementia, neurological D/O, initiation of CPAP for OSA, diagnosis of a new neurological D/O Statistical: Gender, AHI, anxiety, depression, use of sleep meds
Nebes et al., (2009) [19] USA	Cross-sectional	N—157 Mean Age—72.2 % Female—Not provided	SL: Longer SL was associated with poorer global cognitive function but not associated with measures of attention, working memory, processing speed, executive function, and episodic memory. SE: Lower SE was associated with poorer global cognitive function and working memory (N-Back) but not associated with other measures of working memory, processing speed, executive function, and episodic memory. TST: Sleep duration was not associated with any of the cognitive function measures. General Sleep Problems: Higher PSQI scores were associated with poorer global cognitive function, a test of executive function(TMT-B), attention (TMT-B), and working memory (N-Back) but not other tests of executive function, processing speed, episodic memory, and working memory.	Exclusion Criteria: No CNS pathology, substance abuse, taking prescription psychoactive medication, no diagnosis of major depression in last five years or GDS score >15 Statistical: Total depressive score, risk of cerebrovascular disease, use of sleeping pills and anticholinergic meds
Miyata et al., (2013) [20] Japan	Cross-Sectional	N—78 Mean Age—72.2 % Female—79.5	SL: SL not associated with working memory or attention. WASO: WASO not associated with working memory or attention. SE: Lower SE was significantly associated with worse working memory but not attention. TST: Accuracy of 0-back was different for those with <5 h than those with <7 h. No difference was seen between the participants with short and long sleep duration with accuracy on the 1-back test and the attention measure. General Sleep Problems: Global sleep quality was not associated with working memory and attention.	None provided
Chang-Quan, Bi-Rong & Yan, (2012) [21] China	Cross-Sectional	N—660 Mean Age—93.5 % Female—67.3	SL: Longer SL was correlated with cognitive impairment. SE: Lower SE was correlated with cognitive impairment. General Sleep Problems: Poor sleep quality increased the risk for cognitive impairment.	Statistical: Age, gender, education level, serum lipid/lipoprotein, BMI, blood pressure, blood glucose level, smoking habit, alcohol consumption, tea consumption, exercise
Auyeung et al., (2011) [22] China	Cross-Sectional	N—2945 Age—73.9 (±5.0) % Female—40.8	SL: A higher MMSE score was significantly associated with fewer reports of prolonged SL before and after statistical adjustment. TST: Longer nocturnal TST (>7 h) was significantly associated with lower general cognition. No association between global CF and short sleep duration (4 h to 7.9 h). General Sleep Problems: A higher MMSE score was significantly associated with less chronic sleep complaints in the univariate but not multivariate analyses.	Exclusion Criteria: Cognitively incompetent to give informed consent, medical conditions that made them unlikely to complete the study Statistical: Age, gender, MMSE score, education, smoking, alcohol, tea and coffee consumption, habitual smoking, depression (GDS ≥8), use of psychotropic meds, dx of HTN, diabetes, stroke, CHD, COPD
Keage et al., (2012) [23] UK	Cross-Sectional Longitudinal (2 and 10 years)	N-Baseline—2041 2 years—1658 10 years—663 Median age—75 % Female—53	SL: SL was not cross-sectionally associated with cognitive impairment or predicted cognitive decline after 2 or 10 years. WASO: WASO was not cross-sectionally or longitudinally associated with cognitive impairment. TST: Both short (≤6.5 h) and long (≥9 h) sleep duration were not cross-sectionally associated with global cognitive impairment. Short sleep duration was associated with incident cognitive impairment over 10 years. Long sleep duration did not predict risk for cognitive impairment at years two and 10. General Sleep Problems: General sleep problems were not cross-sectionally or longitudinally associated with cognitive impairment.	Statistical: MMSE ≤21 at baseline, sex, age at baseline, BMI classification, education
Potvin et al., (2012) [24] Canada	Longitudinal (1 year)	N—1664 Mean Age Male—72.7 Female—73.9 % Female—69.7	SL: SL was not associated with incident cognitive decline. SE: In women, SE was not associated with incident cognitive decline. In men, sleep efficiency predicted incident cognitive decline after one year. TST: Short sleep duration (≤5 h) was associated with incident cognitive decline in men and not women. In women and not men, long sleep duration (≥9 h) was associated with incident cognitive impairment over one year. General Sleep Problems: In women but not men, PSQI sleep disturbance score was associated with general cognitive decline one year later. In men but not women, global sleep quality score was associated with incident cognitive decline after one year.	Exclusion Criteria: Dementia, Cerebrovascular disease, Brain trauma/tumor/infections, Parkinson’s disease, Epilepsy, Schizophrenia and other forms of psychosis, Baseline MMSE score below the 15th percentile Statistical: Age, education, baseline MMSE score, anxiety, depressive episode psychotropic drug use, cardiovascular conditions score, chronic diseases
Jaussent et al., (2012) [25] France	Longitudinal (8 years)	N—4894 Mean Age—Not provided % Female—57	SOL: SOL not associated with cognitive decline. WASO: As WASO increased, the risk of experiencing cognitive decline increased. General Sleep Problems: Sleep quality not associated with cognitive decline.	Statistical: Study center, sex, age, educational level, MMSE score at baseline, prescribed sleep meds, insomnia severity
Wilckens et al., (2014) [26] USA	Cross-Sectional	N—53 Mean Age—62.68 % Female—Not provided	WASO: Lower WASO was associated with better executive function, verbal fluency, and episodic memory, but not working memory or processing speed. TST: Neither total, long, nor shoet sleep duration were associated with executive function, episodic memory, working memory, verbal fluency or processing speed.	Exclusion Criteria: Self-reported diagnosis of depression, current psychiatric medication use, dependence on drugs or alcohol, diagnosis of a neurodegenerative disease Statistical: Sex, education
McCrae et al., (2012) [27] USA	Cross-Sectional	N—72 Mean Age—70.2 % Female—Not provided	TST: TST did not predict executive functioning or processing speed. General Sleep Problems: Total wake time did not predict executive functioning but significantly predicted processing speed.	Exclusion Criteria: Medical and neurological disorder, psychopathology, sleep disorders (OSA, RLS), MMSE lower than 23, severe depressive symptoms, suspected SDB, missing more than seven days of sleep data
Benito-Leon, Louis & Bermejo-Pareja, (2013) [28] Spain	Longitudinal (3 years)	N—2715 Age—72.9 (±6.1) % Female—56.9	TST: At baseline, short sleep (≤5 h) global CF score was significantly different than reference (6–8 h) group but long sleep (≥9 h) global CF score not significantly different. Longitudinally, change in global CF associated with long sleep but not short sleep. Rate of cognitive decline not significantly different between short sleep and reference but significantly different between long sleep and reference groups. Long sleepers were 1.3 times more likely to have cognitive decline than reference group. Short sleepers’ odds of having cognitive decline similar to reference group.	Exclusion Criteria: Age, gender, geographical area, educational level, diabetes mellitus, chronic obstructive pulmonary disease, depressive symptoms, antidepressant use, medications with central nervous system effects
Virta et al., (2013) [29] Finland	Longitudinal (22.5 years)	N—2336 Mean Age—74.4 % Female—47.9	TST: Short sleep duration (<7 h) and long sleep duration (>8 h) associated with poorer cognition. General Sleep Complaints: Poor sleep quality associated with poorer cognition.	Statistical: Snoring, use of hypnotics and tranquilizers, age, educational level, life satisfaction, obesity, hypertension, leisure time physical activity, alcohol consumption, binge drinking, APOE genotype
Loerbroks et al., (2010) [30] Germany	Cross-Sectional Longitudinal (8.5 years)	N—695 Mean Age—72.1 % Female—59	TST: Short (≤6 h) and long (≥9 h) sleep duration were not cross-sectionally or longitudinally associated with global cognitive function. After statistical adjustment, a decline in sleep duration did not predict global cognitive impairment but an increase in sleep duration was associated with a two-fold increase in global cognitive impairment after 8.5 years.	Exclusion Criteria: Depression, taking mood enhancing drugs Statistical: Age, gender, educational level, physical activity, alcohol consumption, body mass index, smoking status, use of sleep medication, depressive symptoms at the time of testing
Xu et al., (2010) [31] China	Cross Sectional	N—28,670 Mean Age—62 % Female—72.5	TST: Short TST(3–4 h and 5 h) and long TST (more than 10 h) were associated with worse episodic memory and global cognition.	Exclusion Criteria: self-reported mental illness or neurological disease, extremely short or long sleep duration Statistical: Age, sex, employment, occupation, education, smoking, drinking, physical activity, tea consumption, self-rated health, waist circumference, cholesterol, fasting plasma glucose, systolic blood pressure, sleeping duration, napping, insomnia, feeling tired in the morning
Ohayon & Vecchierini, (2002) [32] France	Cross-Sectional	N—1026 Mean age—Not provided % Female—59.8	TST: Short sleep time (<7 h), but not long sleep duration (>8.5 h), was associated with attention-concentration deficits and difficulties in orientation for persons but not praxis, delayed recall, difficulties in temporal orientation, and prospective memory using the McNair Scale. Neither long nor short sleep duration was associated with MMSE.	Statistical: Age, sex, physical activity, occupation, organic diseases, use of sleep or anxiety medications, psychological well being
Faubel et al., (2009) [33] Spain	Cross-Sectional	N—3212 Age—71.6 % Female—52.6	TST: Long sleep duration (>10 h) was associated with an increased risk for cognitive impairment. Short sleep duration (<7 h) was not associated with an increased risk of cognitive impairment. As TST increased from 7 h to 11 h, cognition progressively worsened.	Exclusion Criteria: Diagnosis of depression, extreme sleep duration <4 h or >17 h, dementia diagnosis Statistical: Age sex, physical activity, tobacco use, alcohol consumption, coffee consumption, educational level, SF-36 mental and physical summary scores, night time awakening, BMI, chronic diseases, anxiolytic and medical drug use, HTN, antihypertensive meds, number of social ties, head of family’s work status
Sampaio et al., (2012) [34] Japan	Cross-Sectional	N—145 Mean Age—73 % Female—53.1%	General Sleep Problems: Significant difference reported between good and poor sleepers on global cognition.	Exclusion Criteria: MMSE ≤21, uncontrolled cardiovascular, pulmonary, or metabolic diseases, surgery or forced bedrest in the past three months, current treatment for cancer, orthopedic condition that could restrict ADLs Statistical: Sex, education, living situation, work, financial satisfaction, smoking, alcohol, number of consultations in six months, number of medications, morbidities, comorbidities and regular physical activity categories.
Lim et al., (2013) [35] USA	Prospective Longitudinal (6 years)	N—737 Age—81.6 % Female—76	General Sleep Problems: Increased sleep fragmentation associated with lower baseline global cognition and a more rapid rate of global cognitive decline. Persons with high sleep fragmentation had an increased risk of developing Alzheimer’s disease.	Statistical: Age, sex, education, time
Foley et al. (2001) [36] USA	Longitudinal (3 year)	N—2346 Mean Age—76.6 % Female—0	General Sleep Problems: Having trouble falling asleep or waking up too early and being unable to fall asleep again at baseline was not predictive of global cognition 3 years later.	Exclusion Criteria: Diagnosis of dementia Statistical: Age, education, APOE, CASI score, depressive symptoms, hours of sleep, daytime napping, coronary heart disease, history of stroke
Gamaldo, Allaire & Whitfield, (2008) [37] USA	Cross-Sectional	N—174 Mean Age—72.7 % Female—70.7	General Sleep Problems: There was a negative association between trouble falling asleep and working memory. There were no significant associations between trouble falling sleep and global cognition or episodic memory. Trouble falling asleep predicted working memory but not global cognition or episodic memory after statistical adjustment.	Statistical: Age, gender, education, depression, health, income
Zimmerman et al., (2012) [38] USA	Cross-Sectional	N—549 Mean Age—79.7 % Female—62.1	General Sleep Problems: General sleep onset/maintenance difficulties were not associated with any of the cognition measures.	Exclusion Criteria: Visual and auditory impairment, active psychiatric symptoms, dementia, amnestic MCI Statistical: Age, gender, ethnicity, depression, cardiovascular history
Sutter et al., (2012) [39] Zurich	Cross-Sectional	N—96 Mean Age—72 % Female—57	General Sleep Problems: Poor sleep quality was negatively associated with executive function, verbal fluency, and attention at higher levels of depression. Sleep quality was not associated with processing speed and episodic memory.	Exclusion Criteria: Parkinson’s disease, clinical significant depressive symptoms, use of antidepressants, Statistical: Age, sleep medications

KEY: AHI—Apnea Hypopnea Index; ANCOVA—Analysis of Covariance; APOE—Apolipoprotein E; Att.—Attention; BMI-Body Mass Index; CASI—Cognitive Abilities Screening Instrument; CHD—Coronary Heart Disease; CF—Cognitive Function; CNS—Central Nervous System; COPD—Chronic Obstructive Pulmonary Disease; CPAP—Continuous Positive Airway Pressure; D/O—Disorder; EF—Executive Function; EM—Episodic Memory; FU—Follow-up; GDS—Geriatric Depression Scale; H—Hours; Hx.—History; HTN—Hypertension; IADL—Instrumental Activities of Daily Living; MCI—Mild Cognitive Impairment; MMSE—Mini-Mental State Examination; OSA—Obstructive Sleep Apnea; PS—Processing Speed; PSQI—Pittsburgh Sleep Quality Index; RLS—Restless Legs Syndrome; SDB—Sleep Disordered Breathing; SE—Sleep Efficiency; SF-36—Short-Form-36; SL—Sleep Latency; TMT-B—Trail Making Test B; TST—Total Sleep Time; VF—Verbal Fluency; WASO—Wake After Sleep Onset; WM—Working Memory.