Sleep Disturbances and Cognitive Function in the English Longitudinal Study of Ageing

Background The aim of this study was to investigate whether amnestic (memory) and non-amnestic (non-memory) cognitive function is associated with sleep duration and sleep quality, in younger and older individuals from an ageing population. Methods Participants were 3,968 males and 4,821 females, aged of 50-89 years, from the English Longitudinal Study of Ageing (ELSA). Information on sleep quality and quantity as well as both amnestic and non-amnestic function was available at Wave 4 (2008). Analysis of covariance was used to evaluate the relationship between sleep and cognitive function. Results After adjustment for multiple confounders, in the younger group (50-64 years) duration of sleep explained 15.2% of the variance in the amnestic domain (p=0.003) and 20.6% of non-amnestic cognitive function (p=0.01). In the older group (65+ years) the estimates were 21.3% (p<0.001) and 25.6% (p<0.001), respectively. For sleep quality, there was a statistically significant linear association between sleep quality and both amnestic (p<0.001) and non-amnestic (p<0.001) cognition in the older age group, but no longer in the younger age group (p=0.586 and p=0.373, respectively). Conclusions Cross sectional associations between sleep quantity and quality and different domains of cognitive function vary between younger and older adults. Prospective studies are required to determine the temporal relationships between sleep quantity and quality and changes in cognition in different age groups. Implications Evidence from this cross-sectional analysis contributes to the understanding of the role that disturbed sleep may play in the deterioration of cognition leading to dementia. It will inform discussions regarding the need for improved sleep in the UK and other countries, and provides generalizable evidence for dissemination to the public regarding the importance of sleep in older age. Future Research and Interventions We propose to carry out a prospective analysis of the ELSA data to establish relationships between sleep disturbances and cognitive decline in older adults. If this analysis shows that sleep disturbances play a causal role in cognitive decline and Mild Cognitive Impairment (amnestic and non-amnestic subtypes), then we propose to test early management of sleep disturbances to delay progression of cognitive impairment. In addition, we would work with relevant bodies (e.g. sleep specialists, clinical psychologists, gerontologists) to develop tools to facilitate earlier implementation of behavioural and lifestyle interventions. In turn, this would allow for earlier provisions to be made in the case of dementia diagnoses, helping patients and their families to prepare for, and cope with, the inevitable changes which accompany dementia.