A collection of postings on a range of issues is available on our website (www.mjacksongroup.ca). This month’s post is again from Ken Pope’s listserv, where he kindly provides daily summaries of current articles in the field. The article is as follows:
JAMA Network Open includes an article: “Association Between Sleep Duration and Cognitive Decline.”
The authors are Yanjun Ma, et al.
Here’s how it opens:
The proportion of older people has increased rapidly in recent decades such that 12% of the global population in 2015 was 60 years or older.1 By 2050, this proportion is projected to be greater than one-fifth of the population.1 Consequently, the number of older adults with cognitive impairment and dementia is increasing rapidly.2 Dementia is one of the most common and serious disorders in later life. It is responsible for a large proportion of disability and mortality in older people and imposes a huge burden of long-term care for families and society.3 No effective therapies are available for treating dementia; therefore, the development of dementia prevention strategies has become a priority.4,5 During the long preclinical phase of dementia, accelerated cognitive decline is regarded as a cardinal marker. Thus, the identification of risk factors for cognitive decline is of great significance for dementia prevention.
Previous studies have reported a strong association between sleep and cognitive function in older adults.6 Although a number of cohort studies7-24 have examined whether baseline sleep duration was associated with cognitive decline and incident dementia, the results were inconsistent. Some cohort studies7-11 observed sleep duration to be statistically significantly associated with cognitive decline and incident dementia, whereas other studies12-24 did not reach this conclusion. However, the sample sizes of most previous studies11,12,14-16,18-22,24 were small. In addition, the magnitude of the association between sleep duration, especially extreme sleep duration (≤4 or ≥10 hours per night), and various cognitive domains is unclear. Therefore, a large cohort study is needed to explore the association between sleep duration and the trajectory of cognitive decline.
The English Longitudinal Study of Ageing (ELSA)25 and the China Health and Retirement Longitudinal Study (CHARLS)26 are both nationally representative studies of aging cohorts with multiwave data sets, including cognitive assessments and large sample sizes. These studies enabled investigation of the longitudinal association between baseline sleep duration and consequent cognitive decline. Hence, in the present study, we sought to assess the association between sleep duration and the trajectory of subsequent cognitive decline by pooling and analyzing data from these 2 cohorts.
Another excerpt: “The data were derived from 2 community-based nationally representative longitudinal cohort studies conducted in the United Kingdom and China (waves 4-8 [2008-2009 to 2016-2017] in the ELSA and waves 1 to 3 [2011 to 2015] in the CHARLS) in a population-based setting….”
Here’s how the article concludes: “A statistically significant inverted U-shaped association was observed between sleep duration and cognitive function, as well as subsequent decline. Extreme sleep duration (ie, ≤4 or ≥10 hours per night) was associated not only with lower cognitive function at baseline but also with faster cognitive decline during the follow-up assessments. The inverted U-shaped association indicates that cognitive function should be monitored in middle-aged and older individuals with insufficient or excessive sleep duration. Future mechanism studies and intervention studies examining the association between sleep duration and cognitive decline are needed.”
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“Sleep that knits up the raveled sleeve of care, The death of each day’s life, sore labor’s bath, Balm of hurt minds, great nature’s second course, Chief nourisher in life’s feast… Sleep that relieves the weary laborer and heals hurt minds.”—MacBeth, Act II, Scene 2