Longer Duration of Sleep and Risk of Cognitive Decline: A Meta-Analysis of Observational Studies.

BACKGROUND: Previous observational epidemiological studies have reported inconsistent findings about the association between longer durations of sleep and the risk of cognitive impairment and dementia. To investigate the association between longer durations of sleep and the risk of cognitive decline, we performed a meta-analysis of observational studies.

METHODS: We searched PubMed, EMBASE, and the bibliographies of relevant articles to retrieve additional studies in July 2015. A total of 53,942 participants (mean age 66.9 years) were included in the final analysis. Three evaluators independently reviewed and selected articles, based on pre-determined selection criteria.

RESULTS: Among a total of 695 articles, 10 observational epidemiological studies with 3 case-control studies and 7 cohort studies were included in the final analysis. Compared to the average sleep duration, the odds ratio or relative risk of the longest sleep duration was 1.42 (95% CI 1.27-1.59) for cognitive decline in the fixed-effect meta-analysis, 1.38 for cognitive impairment (95% CI 1.23-1.56), and 1.42 for dementia (95% CI 1.15-1.77). Subgroup meta-analyses by various factors such as study design, type of cognitive decline, gender, region, age, and methodological quality of study showed consistent findings.

CONCLUSION: The current meta-analysis found that longer duration of sleep is associated with an increased risk of cognitive decline.