Sleep Quality and Cognitive Function in Healthy Old Age: The Moderating Role of Subclinical Depression

Objective: Previous research has yielded inconclusive results on the relationship between self-reported sleep quality and cognitive performance in healthy old age. Discrepant findings have been reported regarding processing speed and attention, executive functions, and episodic memory. However, sleep quality has also been found to be related to cognitive performance in patients with depression. Our aim was to clarify the relationship between sleep quality and cognitive performance in healthy older adults, and to evaluate the moderating role of subclinical depression on this relationship. Method: The Pittsburgh Sleep Quality Index was used to assess subjective sleep quality in 107 participants (age >= 61 years). A broad battery of neuropsychological tests measured basic cognitive processes, executive functions, and memory processes. Results: Subclinical depression moderated the link between sleep quality and cognitive performance. More precisely, poorer sleep quality was associated with lower performance in reasoning, semantic fluency, and shifting in those with high versus low levels of subclinical depression. Conclusion: Our findings suggest that poor sleep quality might affect higher order cognitive processes, particularly in those reporting higher levels of subclinical depression. Findings on the relationships between sleep quality, cognitive functioning, and depressive symptomatology are discussed in relation to neurobehavioral theories of sleep.