Duration and Quality of Sleep as Risk Factors for Cognitive Impairment: An Umbrella Review of Systematic Reviews

The 2020 Lancet Commission report on dementia prevention, intervention, and care, as well as its 2024 update, did not include sleep duration or sleep quality among the identified modifiable risk factors for dementia. Emerging evidence, however, supports a renewed, systematic reappraisal of the relationship between sleep parameters and cognitive impairment.

An umbrella review was conducted to comprehensively evaluate the associations between sleep duration, sleep quality, and cognitive decline. This review was registered with PROSPERO (CRD420250655199) and adhered to PRISMA guidelines, as reported in the PRIOR checklist. Major electronic databases, including PubMed, Ovid MEDLINE, PsycINFO, and Google Scholar, were systematically searched for peer-reviewed systematic reviews and meta-analyses up to the end of February 2025. Eligible reviews included observational studies (cohort, cross-sectional, or case-control) examining sleep duration or sleep quality as exposures and irreversible cognitive decline or dementia as outcomes. Quality was assessed using the CASP tool. Reviews primarily focusing on parasomnias or sleep apnea were excluded.

Of 786 records identified, 13 systematic reviews met the inclusion criteria, including 11 with meta-analyses. Five reviews reported associations with long sleep duration, six with short sleep duration, and three reported no significant association with short sleep duration. Among five cohort-based reviews, three consistently supported an association between sleep duration and cognitive decline. Two of three low-bias reviews also supported this association. No low-risk or cohort-only reviews specifically examined sleep quality. Two reviews assessing both duration and quality of sleep reported increased dementia risk. Overall, pooled evidence from cohort-only and low-bias reviews supported a U-shaped association between sleep duration and cognitive impairment, with longitudinal data suggesting temporal directionality.

As most evidence was rated low certainty by GRADE, these findings should be considered supplementary to the 2024 Lancet Commission report. As the first rigorously conducted umbrella review, this review consolidates existing evidence and highlights the need for well-designed prospective research to clarify the independent effects of sleep duration and quality on cognition.