Aging Clin Exp Res DOI 10.1007/s40520-015-0388-2
ORIGINAL ARTICLE
Longer self-reported sleep duration is associated with decreased performance on the montreal cognitive assessment in older adults Michael Malek-Ahmadi1 • Krishna Kora1 • Kathy O’Connor1 • Sharon Schofield1 David Coon2 • Walter Nieri1
•
Received: 27 February 2015 / Accepted: 22 May 2015 Ó Springer International Publishing Switzerland 2015
Abstract Background Previous studies investigating the relationship between sleep duration and cognitive function in older adults have suggested that longer sleep durations are associated with decreased cognitive performance. Aim The intent of this study is to determine if performance on the Montreal Cognitive Assessment (MoCA) and the Mini Mental State Exam (MMSE) is associated with self-reported sleep duration in older adults. Methods Data from 189 cognitively normal older adults aged 75 and older (mean age 89.29 ± 7.62) and free of severe depression were used for this analysis. Individuals were grouped based on their self-reported hours of sleep (short duration = \7, normal duration = 7, [9, and long duration = C9). The Kruskal–Wallis test was used to discern group differences on the MoCA scores, while multinomial logistic regression was used to assess the association between MoCA and MMSE scores and sleep group. Results The long duration group had significantly lower MoCA scores than the normal duration group (p = 0.02). The short duration group was not significantly different from the normal duration group (p = 0.33). Individuals in the short duration group were more likely to have higher MoCA scores than those in long duration group after adjusting for age, gender, and presence of depressive symptoms [OR 0.86, 95 % CI (0.76, 0.98), p = 0.02].
& Michael Malek-Ahmadi [email protected] 1
Center for Healthy Aging, Banner Sun Health Research Institute, 10515 W. Santa Fe Drive, Sun City, AZ 85351, USA
2
College of Nursing and Health Innovation, Arizona State University, 530 N. 3rd St., Phoenix, AZ 85004, USA
Conclusion The results of this study suggest that in a group of non-demented, very old subjects, self-reported sleep duration of nine or more hours is associated with decreased cognitive performance on the MoCA in older adults, even after accounting for age, gender, and presence of depressive symptoms. Keywords Cognition Aged 80 and over Geriatrics Cognitive decline
Introduction The association between sleep duration and cognitive function has been widely studied across various age ranges but is of particular importance among older adults, given that changes in sleep duration and cognitive performance are quite prevalent in this group. Studies investigating the relationship between sleep duration and cognitive function in older adults have found that increased sleep duration is associated with decreased performance on cognitive tests [1–3]. However, others have found that both short and long sleep duration are associated with decreased cognitive performance [4] and that excessive daytime sleepiness is associated with an increased risk in cognitive decline among older adults [5, 6]. The methodology used to assess cognitive function as it relates to sleep duration has varied substantially between studies with some utilizing several cognitive tests [1, 2, 4, 7, 8] and others using only the Mini Mental State Exam (MMSE) [3, 5, 6]. Chen and colleagues [9] used the Montreal Cognitive Assessment (MoCA) to measure cognitive function in individuals with sleep apnea; however, there do not appear to be any studies in which the MoCA has been used to assess the association between sleep duration and cognitive function in older adults.
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Recent studies have suggested that the MoCA is superior to the MMSE in terms of its sensitivity to cognitive decline [10, 11]. Characterizing MoCA performance in contrast to the MMSE with regard to sleep duration in older adults would be a substantive contribution to the body of knowledge relevant to both clinical research and practice. In particular, characterizing this association in the oldest old (individuals aged 80 and older) is especially of interest since this is the fastest growing age group in the United States [12]. Therefore, the key aim of this study is to characterize MoCA performance as it relates to sleep duration in older adults.
Methods Study participants Data from 189 participants in an on-going study on longevity were used for this analysis. Participants are assessed annually on a number of cognitive, medical, psychosocial, and demographic measures to identify factors associated with increased longevity. Participants were recruited throughout Arizona, mainly from the Phoenix metropolitan area through advertisements, community talks, and referrals from physicians and other study participants. Individuals with a history of stroke, dementia, or other neurological conditions that could result in cognitive impairment were excluded. Individuals with a score of C10 on the Centers for Epidemiologic Studies Short-Depression scale (CES-D) were excluded to rule out the effect of depression. The sample was divided into three groups based on their reported number of sleep hours (short duration = \7, normal duration = C7,\9, long duration = C9). Assessments The Montreal Cognitive Assessment (MoCA) is a brief cognitive screening instrument that assesses a variety of cognitive functions and scored on 30-point scale with Table 1 Demographic and clinical data for short, normal, and long sleep duration groups
higher scores representing better cognitive function [13]. The Mini Mental State Exam (MMSE) [14] is another widely used cognitive screening instrument that assesses a variety of cognitive functions and is scored on 30-point scale with higher scores representing better cognitive function. The CES-D is a scale that assesses the presence and frequency of depressive symptoms [15]. Hours of sleep per night was obtained via self-report for each participant. Statistical analysis The Kruskal–Wallis test was used to assess differences in MoCA and MMSE scores between the three sleep groups. A non-parametric test was used since both MoCA and MMSE scores were not normally distributed. Multinomial logistic regression was used to quantify the magnitude of the association for both MoCA and MMSE performance on sleep duration. Crude analyses used MoCA and MMSE scores as the predictor variable and sleep group as the outcome variable, using the normal duration group as the reference group. Adjusted analyses included age, gender, and CES-D score in addition to MoCA and MMSE scores to account for their effects.
Results Demographic characteristics of the study sample are shown in Table 1. As a whole, the sample had an average age at the time of evaluation of 89.29 ± 7.62 with a range of 75–10. The average reported sleep duration for the sample was 7.27 ± 1.21 h with a range of 4–12. The sample comprised of 65 males and 124 females (35 and 65 %, respectively). The long duration group was significantly older than both the normal duration and the short duration groups (p = 0.04 and p = 0.005, respectively). No significant differences in CESS-D scores were noted between each of the groups (p = 0.25) and there was no significant difference in the distribution of males and females among the three groups (p = 0.50). The long duration group had
Short duration
Normal duration
Long duration
Total
N
59 (31 %)
107 (57 %)
23 (12 %)
189
Gender (M/F)
19/40
37/70
9/14
65/124
Age
89.24 ± 7.32
88.73 ± 7.71
92.00 ± 7.70
89.29 ± 7.62
CES-D
3.44 ± 2.74
2.76 ± 2.40
2.57 ± 2.45
2.95 ± 2.53
MoCA
25 (22.25, 27)
25 (23, 28)
23 (22, 25)
25 (23, 27)
MMSE
29 (28, 30)
29 (28, 30)
28 (25.25, 29)
29 (28, 30)
Age and CES-D: mean ± standard deviation MoCA and MMSE: median (interquartile range)
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significantly lower MoCA scores than both the normal duration and the short duration groups (p = 0.002 and p = 0.02, respectively; Fig. 1). MMSE scores showed a similar pattern of significant differences as the long duration group was significantly lower than both the normal duration and the short duration groups (p = 0.001 and p = 0.003, respectively; Fig. 2). Results of the logistic regression analyses are shown in Table 2. No significant association between MoCA performance and the short duration group was found both in the crude (OR 0.96, 95 % CI 0.88, 1.04, p = 0.28) and adjusted (OR 0.97, 95 % CI 0.89, 1.06, p = 0.46) analyses. In the long duration group, both the crude (OR 0.82, 95 % CI 0.73, 0.93, p = 0.001) and adjusted (OR 0.86, 95 % CI 0.76, 0.98, p = 0.02) analyses yielded statistically significant associations indicating that the lower MoCA scores were more likely to occur in this group relative to the normal duration group (Table 2). For the MMSE, no significant associations were found for short duration group in both the crude (OR 0.98, 95 % 30 28
MoCA Score
26 24 22 20 18 16 14 Long
Normal
Short
Sleep Duration
Fig. 1 MoCA score comparison for short, normal, and long sleep duration groups
CI 0.84, 1.15, p = 0.83) and adjusted (OR 0.99, 95 % CI 0.84, 1.18, p = 0.92) analyses. For the long duration group, the association was significant in the crude analysis (OR 0.77, 95 % CI 0.64, 0.93, p = 0.006), but failed to show significance in the adjusted analysis (OR 0.83, 95 % CI: 0.68, 1.01, p = 0.07).
Discussion The results of this study show that increased sleep duration in very old, non-demented adults is associated with decreased cognitive performance on the MoCA. This association remained significant after adjusting for age, gender, and presence of depressive symptoms. The MMSE also showed a significant inverse association with sleep duration in the crude analysis; however, this association was not significant after adjusting for age, gender, and presence of depressive symptoms. Other cross-sectional studies have noted similar findings using different cognitive instruments [18, 19]. Schmutte et al. [8] used a sample that was very similar to ours (non-demented older adults age 75–85) and also found that decreased cognitive performance was associated with increased perceived sleep duration. Jaussent and colleagues [5] included a relatively large group of individuals aged 80 and older (N = 400), but this subgroup was not analyzed separately. It is noted that the study by Jaussent et al. [5] was longitudinal and assessed the association between cognition and excessive daytime sleepiness, so it is difficult to make a direct comparison of these results to our current study. Aside from these studies, other studies investigating the relationship between sleep duration and cognition in older adults do not address their findings specifically to the oldest old. Given that the proportion of individuals in this age group continues to increase among the general population [12], identifying and addressing risk factors that may lead to cognitive impairment is increasingly important. This is
Table 2 Crude and adjusted association of MoCA and MMSE scores as predictors of sleep duration group MoCA
MMSE
Short duration vs normal duration: crude
0.96 (0.88, 1.04)
0.98 (0.84, 1.15)
Short duration vs normal duration: adjusted for age, gender, and CES-D
p = 0.28 0.97 (0.89, 1.06)
p = 0.83 0.99 (0.84, 1.18)
p = 0.46
p = 0.92
Long duration vs normal duration: crude Long duration vs normal duration: adjusted for age, gender, and CES-D
0.82 (0.73, 0.93)
0.77 (0.64, 0.93)
p = 0.001
p = 0.006
0.86 (0.76, 0.98)
0.83 (0.68, 1.01)
p = 0.02
p = 0.07
Odds ratio (95 % confidence interval) p value
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MMSE Score
28
26
24
22
20 Long
Normal
Short
Sleep Duration
Fig. 2 MMSE score comparison for short, normal, and long sleep duration groups
of particular concern given that this age group is at the highest risk for developing Alzheimer’s disease (AD) [16]. Although this study did not control for psychotropic medication use and medical comorbidities that may contribute to sleep quality and duration, others have highlighted the importance of depressive symptoms in the association between sleep duration and cognitive function. This study excluded individuals whose CES-D scores were indicative of depression (CES-D greater than 10) which allowed us to rule out a significant confounding variable. However, CES-D scores were still used in the statistical models to account for the presence of any depressive symptoms that may have impacted sleep duration. By doing so, this study found that decreased cognitive performance was associated with increased sleep duration, independent of depressive symptoms. Our findings extend prior research by recruiting a sample of very old subjects without dementia and severe depression. The use of both the MoCA and MMSE in this study underscores the importance of test selection for studies investigating the association between sleep duration and cognitive function. After adjusting for confounding variables, only the MoCA showed a significant association with sleep duration. Previous studies have found similar associations between the MMSE and sleep duration [3, 5, 6] while others have used more extensive batteries of cognitive tests and have also found similar results [1, 2, 4, 7, 8]. While the use of a variety of tests is advantageous as it may demonstrate which cognitive domains are most affected by sleep duration, the MoCA is a viable alternative when it is not feasible to collect data for several tests. The MoCA’s short administration time and sensitivity to cognitive changes may make it a useful tool when assessing cognitive changes associated with sleep duration. Although
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the MMSE has been used in other studies investigating the association between sleep duration and cognitive function, our results suggest the MoCA may be provide a more accurate assessment of this association in terms of its sensitivity to cognitive changes [10, 11]. The implications of this study are highlighted by Yaffe and colleagues [17] who cite several studies showing that longer sleep duration was associated with a greater risk for cognitive impairment and dementia. Jaussent and colleagues [5] suggest that sleep changes, particularly excessive daytime sleepiness (EDS), may be an early marker of cognitive decline that may eventually progress to a dementia. Merlino and colleagues [6] appear to confirm this hypothesis with their study that found EDS to be independently associated with dementia status. In addition, they found that EDS frequency increased as the severity of cognitive impairment increased. Although the current study measured self-reported nocturnal sleep duration, the findings of this study complement those cited above in terms of the relationship between sleep and decreased cognitive performance in older adults. In particular, the increased risk of dementia associated with increased sleep duration is also very important given that the risk of AD increases with age [16]. Yaffe and colleagues [17] suggest that factors such as circadian rhythm disturbances and neurodegenerative processes may contribute to the manifestation of sleep disturbances and decreased cognitive performance, so it is possible that addressing sleep disturbances in clinical settings may provide some benefit to older adults in terms of risk reduction for incident cognitive impairment and dementia. Through the use of actigraphy, it has been suggested that increased sleep fragmentation is associated with decreased cognitive performance [1] and so it is possible that individuals who report longer sleep duration may do so because of more frequent nighttime wakings or because of increased time spent in bed. Although this study was not able to assess the prognostic risk of increased sleep duration on incident dementia, it does demonstrate that increased sleep duration is associated with decreased cognitive performance in cognitively normal individuals and could be an early marker of incident cognitive decline. Health care providers should make it a priority to ask their patients about their sleep history and in particular duration of sleep along with routine memory screening in an effort to identify and manage these problems sooner. Acknowledgments The authors would like to thank Drs. Marwan Sabbagh and Brittany Dugger for their review and commentary on this manuscript. Funding for this study was provided by the Arizona Alzheimer’s Research Center (AZDHS agreement # AGR2009-017) and Arizona State University, College of Human Services Centenarian Database contract, 2007–2008. These entities’ involvement in the study was limited to financial support.
Aging Clin Exp Res Conflict of interest of interest.
The authors declare that they have no conflict 9.
Human and Animal Rights All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Informed consent Informed consent was obtained from all individual participants included in the study. All participants signed an informed consent form prior to being interviewed. Approval for the study was granted by the Banner Health Internal Review Board.
References 1. Blackwell T, Yaffe K, Ancoli-Israel S et al (2011) Association of sleep characteristics and cognition in older community-dwelling men: the MrOS Sleep Study. Sleep 34:1347–1356 2. Ferrie JE, Shipley MJ, Akbaraly TN et al (2011) Change in sleep duration and cognitive function: findings from the Whitehall II Study. Sleep 34:565–573A 3. Potvin O, Lorrain D, Forget H et al (2011) Sleep quality and 1-year incident cognitive impairment in community-dwelling older adults. Sleep 35:491–499 4. Kronholm E, Sallinen M, Suutama T et al (2009) Self-reported sleep duration and cognitive functioning in the general population. J Sleep Res 18:436–446 5. Jaussent I, Bouyer J, Ancelin M-A et al (2012) Excessive sleepiness is predictive of cognitive decline in the elderly. Sleep 35:1201–1207 6. Merlino G, Piani A, Gigli GL et al (2010) Daytime sleepiness is associated with dementia and cognitive decline in older Italian adults: a population-based study. Sleep Med 11:372–377 7. Nebes RD, Buysse DJ, Halligan EM et al (2009) Self-reported sleep quality predicts poor cognitive performance in healthy older adults. J Gerontol B Psychol Sci Soc Sci 64B:180–187 8. Schmutte T, Harris S, Levin R et al (2007) The relation between cognitive functioning and self-reported sleep complaints in
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nondemented older adults: results from the Bronx Aging Study. Behav Sleep Med 5:39–56 Chen R, Xiong K-P, Huang J-Y et al (2011) Neurocognitive impairment in Chinese patients with obstructive sleep apnoea hypopnoea syndrome. Respirology 16:842–848 Alagiakrishnan K, Zhao N, Mereu L et al (2013) Montreal cognitive assessment is superior to standardized mini-mental status exam in detecting mild cognitive impairment in the middle-aged and elderly patients with type 2 diabetes mellitus. Biomed Res Int 2013:186106 Wang CS, Pai MC, Chen PL et al (2013) Montreal Cognitive Assessment and Mini-Mental State Examination performance in patients with mild-to-moderate dementia with Lewy bodies, Alzheimer’s disease, and normal participants in Taiwan. Int Psychogeriatr 25:1839–1848 National Institute on Aging (2011) Global health and aging. http://www.nia.nih.gov/research/publication/global-health-andaging/living-longer. Accessed 24 Dec 2014 Nasreddine ZS, Phillips NA, Bedirian V et al (2005) The Montreal Cognitive Assessment, MoCA: a brief screening tool for mild cognitive impairment. J Am Geriatr Soc 53:695–699 Folstein MF, Folstein SE, McHugh PR (1975) ‘‘Mini-mental state’’. A practical method for grading the cognitive state of patients for the clinician. J Psychiatr Res 12:189–198 Andresen EM, Malmgreen JA, Carter WB et al (1994) Screening for depression in well older adults: evaluation of a short form of the CES-D (Center for Epidemiologic Studies Depression Scale). Am J Prev Med 10:77–84 Alzheimer’s Association (2014) Alzheimer’s disease facts and figures 2014. http://www.alz.org/alzheimers_disease_21590.asp. Accessed 13 Feb 2015 Yaffe K, Falvey CM, Hoang T (2014) Connections between sleep and cognition in older adults. Lancet Neurol 13:1017–1028 Tworoger SS, Lee S, Schernhammer ES et al (2006) The association of self-reported sleep duration, difficulty sleeping, and snoring with cognitive function in older women. Alzheimer Dis Assoc Disord 20:41–48 Xu L, Jiang CQ, Lam TH et al (2011) Short or long sleep duration is associated with memory impairment in older Chinese: the Guangzhou Biobank Cohort Study. Sleep 34:575–580
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ORIGINAL ARTICLE
Longer self-reported sleep duration is associated with decreased performance on the montreal cognitive assessment in older adults Michael Malek-Ahmadi1 • Krishna Kora1 • Kathy O’Connor1 • Sharon Schofield1 David Coon2 • Walter Nieri1
•
Received: 27 February 2015 / Accepted: 22 May 2015 Ó Springer International Publishing Switzerland 2015
Abstract Background Previous studies investigating the relationship between sleep duration and cognitive function in older adults have suggested that longer sleep durations are associated with decreased cognitive performance. Aim The intent of this study is to determine if performance on the Montreal Cognitive Assessment (MoCA) and the Mini Mental State Exam (MMSE) is associated with self-reported sleep duration in older adults. Methods Data from 189 cognitively normal older adults aged 75 and older (mean age 89.29 ± 7.62) and free of severe depression were used for this analysis. Individuals were grouped based on their self-reported hours of sleep (short duration = \7, normal duration = 7, [9, and long duration = C9). The Kruskal–Wallis test was used to discern group differences on the MoCA scores, while multinomial logistic regression was used to assess the association between MoCA and MMSE scores and sleep group. Results The long duration group had significantly lower MoCA scores than the normal duration group (p = 0.02). The short duration group was not significantly different from the normal duration group (p = 0.33). Individuals in the short duration group were more likely to have higher MoCA scores than those in long duration group after adjusting for age, gender, and presence of depressive symptoms [OR 0.86, 95 % CI (0.76, 0.98), p = 0.02].
& Michael Malek-Ahmadi [email protected] 1
Center for Healthy Aging, Banner Sun Health Research Institute, 10515 W. Santa Fe Drive, Sun City, AZ 85351, USA
2
College of Nursing and Health Innovation, Arizona State University, 530 N. 3rd St., Phoenix, AZ 85004, USA
Conclusion The results of this study suggest that in a group of non-demented, very old subjects, self-reported sleep duration of nine or more hours is associated with decreased cognitive performance on the MoCA in older adults, even after accounting for age, gender, and presence of depressive symptoms. Keywords Cognition Aged 80 and over Geriatrics Cognitive decline
Introduction The association between sleep duration and cognitive function has been widely studied across various age ranges but is of particular importance among older adults, given that changes in sleep duration and cognitive performance are quite prevalent in this group. Studies investigating the relationship between sleep duration and cognitive function in older adults have found that increased sleep duration is associated with decreased performance on cognitive tests [1–3]. However, others have found that both short and long sleep duration are associated with decreased cognitive performance [4] and that excessive daytime sleepiness is associated with an increased risk in cognitive decline among older adults [5, 6]. The methodology used to assess cognitive function as it relates to sleep duration has varied substantially between studies with some utilizing several cognitive tests [1, 2, 4, 7, 8] and others using only the Mini Mental State Exam (MMSE) [3, 5, 6]. Chen and colleagues [9] used the Montreal Cognitive Assessment (MoCA) to measure cognitive function in individuals with sleep apnea; however, there do not appear to be any studies in which the MoCA has been used to assess the association between sleep duration and cognitive function in older adults.
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Recent studies have suggested that the MoCA is superior to the MMSE in terms of its sensitivity to cognitive decline [10, 11]. Characterizing MoCA performance in contrast to the MMSE with regard to sleep duration in older adults would be a substantive contribution to the body of knowledge relevant to both clinical research and practice. In particular, characterizing this association in the oldest old (individuals aged 80 and older) is especially of interest since this is the fastest growing age group in the United States [12]. Therefore, the key aim of this study is to characterize MoCA performance as it relates to sleep duration in older adults.
Methods Study participants Data from 189 participants in an on-going study on longevity were used for this analysis. Participants are assessed annually on a number of cognitive, medical, psychosocial, and demographic measures to identify factors associated with increased longevity. Participants were recruited throughout Arizona, mainly from the Phoenix metropolitan area through advertisements, community talks, and referrals from physicians and other study participants. Individuals with a history of stroke, dementia, or other neurological conditions that could result in cognitive impairment were excluded. Individuals with a score of C10 on the Centers for Epidemiologic Studies Short-Depression scale (CES-D) were excluded to rule out the effect of depression. The sample was divided into three groups based on their reported number of sleep hours (short duration = \7, normal duration = C7,\9, long duration = C9). Assessments The Montreal Cognitive Assessment (MoCA) is a brief cognitive screening instrument that assesses a variety of cognitive functions and scored on 30-point scale with Table 1 Demographic and clinical data for short, normal, and long sleep duration groups
higher scores representing better cognitive function [13]. The Mini Mental State Exam (MMSE) [14] is another widely used cognitive screening instrument that assesses a variety of cognitive functions and is scored on 30-point scale with higher scores representing better cognitive function. The CES-D is a scale that assesses the presence and frequency of depressive symptoms [15]. Hours of sleep per night was obtained via self-report for each participant. Statistical analysis The Kruskal–Wallis test was used to assess differences in MoCA and MMSE scores between the three sleep groups. A non-parametric test was used since both MoCA and MMSE scores were not normally distributed. Multinomial logistic regression was used to quantify the magnitude of the association for both MoCA and MMSE performance on sleep duration. Crude analyses used MoCA and MMSE scores as the predictor variable and sleep group as the outcome variable, using the normal duration group as the reference group. Adjusted analyses included age, gender, and CES-D score in addition to MoCA and MMSE scores to account for their effects.
Results Demographic characteristics of the study sample are shown in Table 1. As a whole, the sample had an average age at the time of evaluation of 89.29 ± 7.62 with a range of 75–10. The average reported sleep duration for the sample was 7.27 ± 1.21 h with a range of 4–12. The sample comprised of 65 males and 124 females (35 and 65 %, respectively). The long duration group was significantly older than both the normal duration and the short duration groups (p = 0.04 and p = 0.005, respectively). No significant differences in CESS-D scores were noted between each of the groups (p = 0.25) and there was no significant difference in the distribution of males and females among the three groups (p = 0.50). The long duration group had
Short duration
Normal duration
Long duration
Total
N
59 (31 %)
107 (57 %)
23 (12 %)
189
Gender (M/F)
19/40
37/70
9/14
65/124
Age
89.24 ± 7.32
88.73 ± 7.71
92.00 ± 7.70
89.29 ± 7.62
CES-D
3.44 ± 2.74
2.76 ± 2.40
2.57 ± 2.45
2.95 ± 2.53
MoCA
25 (22.25, 27)
25 (23, 28)
23 (22, 25)
25 (23, 27)
MMSE
29 (28, 30)
29 (28, 30)
28 (25.25, 29)
29 (28, 30)
Age and CES-D: mean ± standard deviation MoCA and MMSE: median (interquartile range)
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significantly lower MoCA scores than both the normal duration and the short duration groups (p = 0.002 and p = 0.02, respectively; Fig. 1). MMSE scores showed a similar pattern of significant differences as the long duration group was significantly lower than both the normal duration and the short duration groups (p = 0.001 and p = 0.003, respectively; Fig. 2). Results of the logistic regression analyses are shown in Table 2. No significant association between MoCA performance and the short duration group was found both in the crude (OR 0.96, 95 % CI 0.88, 1.04, p = 0.28) and adjusted (OR 0.97, 95 % CI 0.89, 1.06, p = 0.46) analyses. In the long duration group, both the crude (OR 0.82, 95 % CI 0.73, 0.93, p = 0.001) and adjusted (OR 0.86, 95 % CI 0.76, 0.98, p = 0.02) analyses yielded statistically significant associations indicating that the lower MoCA scores were more likely to occur in this group relative to the normal duration group (Table 2). For the MMSE, no significant associations were found for short duration group in both the crude (OR 0.98, 95 % 30 28
MoCA Score
26 24 22 20 18 16 14 Long
Normal
Short
Sleep Duration
Fig. 1 MoCA score comparison for short, normal, and long sleep duration groups
CI 0.84, 1.15, p = 0.83) and adjusted (OR 0.99, 95 % CI 0.84, 1.18, p = 0.92) analyses. For the long duration group, the association was significant in the crude analysis (OR 0.77, 95 % CI 0.64, 0.93, p = 0.006), but failed to show significance in the adjusted analysis (OR 0.83, 95 % CI: 0.68, 1.01, p = 0.07).
Discussion The results of this study show that increased sleep duration in very old, non-demented adults is associated with decreased cognitive performance on the MoCA. This association remained significant after adjusting for age, gender, and presence of depressive symptoms. The MMSE also showed a significant inverse association with sleep duration in the crude analysis; however, this association was not significant after adjusting for age, gender, and presence of depressive symptoms. Other cross-sectional studies have noted similar findings using different cognitive instruments [18, 19]. Schmutte et al. [8] used a sample that was very similar to ours (non-demented older adults age 75–85) and also found that decreased cognitive performance was associated with increased perceived sleep duration. Jaussent and colleagues [5] included a relatively large group of individuals aged 80 and older (N = 400), but this subgroup was not analyzed separately. It is noted that the study by Jaussent et al. [5] was longitudinal and assessed the association between cognition and excessive daytime sleepiness, so it is difficult to make a direct comparison of these results to our current study. Aside from these studies, other studies investigating the relationship between sleep duration and cognition in older adults do not address their findings specifically to the oldest old. Given that the proportion of individuals in this age group continues to increase among the general population [12], identifying and addressing risk factors that may lead to cognitive impairment is increasingly important. This is
Table 2 Crude and adjusted association of MoCA and MMSE scores as predictors of sleep duration group MoCA
MMSE
Short duration vs normal duration: crude
0.96 (0.88, 1.04)
0.98 (0.84, 1.15)
Short duration vs normal duration: adjusted for age, gender, and CES-D
p = 0.28 0.97 (0.89, 1.06)
p = 0.83 0.99 (0.84, 1.18)
p = 0.46
p = 0.92
Long duration vs normal duration: crude Long duration vs normal duration: adjusted for age, gender, and CES-D
0.82 (0.73, 0.93)
0.77 (0.64, 0.93)
p = 0.001
p = 0.006
0.86 (0.76, 0.98)
0.83 (0.68, 1.01)
p = 0.02
p = 0.07
Odds ratio (95 % confidence interval) p value
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MMSE Score
28
26
24
22
20 Long
Normal
Short
Sleep Duration
Fig. 2 MMSE score comparison for short, normal, and long sleep duration groups
of particular concern given that this age group is at the highest risk for developing Alzheimer’s disease (AD) [16]. Although this study did not control for psychotropic medication use and medical comorbidities that may contribute to sleep quality and duration, others have highlighted the importance of depressive symptoms in the association between sleep duration and cognitive function. This study excluded individuals whose CES-D scores were indicative of depression (CES-D greater than 10) which allowed us to rule out a significant confounding variable. However, CES-D scores were still used in the statistical models to account for the presence of any depressive symptoms that may have impacted sleep duration. By doing so, this study found that decreased cognitive performance was associated with increased sleep duration, independent of depressive symptoms. Our findings extend prior research by recruiting a sample of very old subjects without dementia and severe depression. The use of both the MoCA and MMSE in this study underscores the importance of test selection for studies investigating the association between sleep duration and cognitive function. After adjusting for confounding variables, only the MoCA showed a significant association with sleep duration. Previous studies have found similar associations between the MMSE and sleep duration [3, 5, 6] while others have used more extensive batteries of cognitive tests and have also found similar results [1, 2, 4, 7, 8]. While the use of a variety of tests is advantageous as it may demonstrate which cognitive domains are most affected by sleep duration, the MoCA is a viable alternative when it is not feasible to collect data for several tests. The MoCA’s short administration time and sensitivity to cognitive changes may make it a useful tool when assessing cognitive changes associated with sleep duration. Although
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the MMSE has been used in other studies investigating the association between sleep duration and cognitive function, our results suggest the MoCA may be provide a more accurate assessment of this association in terms of its sensitivity to cognitive changes [10, 11]. The implications of this study are highlighted by Yaffe and colleagues [17] who cite several studies showing that longer sleep duration was associated with a greater risk for cognitive impairment and dementia. Jaussent and colleagues [5] suggest that sleep changes, particularly excessive daytime sleepiness (EDS), may be an early marker of cognitive decline that may eventually progress to a dementia. Merlino and colleagues [6] appear to confirm this hypothesis with their study that found EDS to be independently associated with dementia status. In addition, they found that EDS frequency increased as the severity of cognitive impairment increased. Although the current study measured self-reported nocturnal sleep duration, the findings of this study complement those cited above in terms of the relationship between sleep and decreased cognitive performance in older adults. In particular, the increased risk of dementia associated with increased sleep duration is also very important given that the risk of AD increases with age [16]. Yaffe and colleagues [17] suggest that factors such as circadian rhythm disturbances and neurodegenerative processes may contribute to the manifestation of sleep disturbances and decreased cognitive performance, so it is possible that addressing sleep disturbances in clinical settings may provide some benefit to older adults in terms of risk reduction for incident cognitive impairment and dementia. Through the use of actigraphy, it has been suggested that increased sleep fragmentation is associated with decreased cognitive performance [1] and so it is possible that individuals who report longer sleep duration may do so because of more frequent nighttime wakings or because of increased time spent in bed. Although this study was not able to assess the prognostic risk of increased sleep duration on incident dementia, it does demonstrate that increased sleep duration is associated with decreased cognitive performance in cognitively normal individuals and could be an early marker of incident cognitive decline. Health care providers should make it a priority to ask their patients about their sleep history and in particular duration of sleep along with routine memory screening in an effort to identify and manage these problems sooner. Acknowledgments The authors would like to thank Drs. Marwan Sabbagh and Brittany Dugger for their review and commentary on this manuscript. Funding for this study was provided by the Arizona Alzheimer’s Research Center (AZDHS agreement # AGR2009-017) and Arizona State University, College of Human Services Centenarian Database contract, 2007–2008. These entities’ involvement in the study was limited to financial support.
Aging Clin Exp Res Conflict of interest of interest.
The authors declare that they have no conflict 9.
Human and Animal Rights All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Informed consent Informed consent was obtained from all individual participants included in the study. All participants signed an informed consent form prior to being interviewed. Approval for the study was granted by the Banner Health Internal Review Board.
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