Association Between Self-Reported Sleep Quality and Conversion From Mild Cognitive Impairment to Dementia: A Retrospective Cohort Study Using the English Longitudinal Study of Ageing

PURPOSE: Poor sleep quality is common in people diagnosed with mild cognitive impairment (MCI) and dementia and may be associated with conversion to dementia. METHOD: This retrospective cohort study investigated the association of self-reported sleep quality and duration with dementia incidence in a cohort of people aged ≥ 50 with MCI from the English Longitudinal Study of Ageing (ELSA) panel study. We identified the MCI cohort using three waves (2008/2009, 2012/2013, 2016/2017) based on absence of diagnosed dementia, self-reported memory problems, preserved ability for daily activities, and reduced cognitive function in neuropsychological assessments. Exposures were self-reported poor sleep quality and sleep duration in the month before the baseline interview. The outcome was self-reported physician-diagnosed dementia from later waves. We modeled associations with Cox proportional hazards regression adjusted for multiple confounders. FINDING: Among 1885 patients with MCI at baseline, 24.7% reported poor sleep quality, 17.6% reported average sleep duration per night to be < 6 h, 74.6% reported average sleep duration per night to be 6-< 9 h, and 7.5% reported average sleep duration per night to be ≥ 9 h. Note that 176 (9.3%) developed dementia during follow-up (median 5.8 years, interquartile range [IQR] 2.1-6.3). Age-adjusted hazard for all-cause dementia, compared to 6-< 9 h sleep duration, was increased with sleep duration ≥ 9 h (hazard ratio [HR] 2.57, 95% confidence interval [CI] 1.62-4.02) but not short sleep duration (HR 0.94, 95% CI 0.55-1.61); there was weak evidence of reduced risk in persons with poor sleep quality, compared to good sleep quality (HR 0.68, 95% CI 0.41-1.12). CONCLUSION: We found evidence for an association between long sleep duration and dementia risk in patients with MCI and limited evidence of an association between poor sleep quality and dementia.