The Relationship Between Insomnia and Cognitive Decline Is Likely Bidirectional

Insomnia and cognitive decline appear bidirectionally related, with each disorder exacerbating the adverse effects of the other. These study findings were recently published in Sleep Medicine.

Insomnia and cognitive impairment are both highly prevalent disorders among older adults. As the life expectancy of the global population continues to rise, there has been increased clinical attention to the connection between insomnia and cognition.

Investigators conducted a literature review to gain a comprehensive understanding of the directionality of the relationship between insomnia and cognitive decline. The investigators searched publication databases to identify studies evaluating insomnia and cognition, published between December 21, 2013 and December 21, 2023. Participants with sleep disorders other than insomnia or with comorbid serious diseases were excluded.

A total of 36 published studies were included in the review. Overall, the studies used 12 indices (both objective and subjective) of sleep status and measured cognitive decline using 34 tests and 5 scales.

The investigators found that individuals with insomnia generally had a significantly greater risk for cognitive decline or Alzheimer disease, relative to those without insomnia. Further, individuals with insomnia vs without displayed significant impairments in attention, memory, visuospatial abilities, executive function, and verbal memory. Overall, 66.67% of studies reported a correlation between insomnia and reductions in cognitive performance. These impairments were also correlated with insomnia severity, as those with more severe insomnia had worse performance across cognitive domains.

The investigators also found that individuals with mild cognitive impairment were more likely to develop sleep disorders like insomnia compared with individuals without cognitive decline. These findings were further supported by brain structure differences in magnetic resonance imaging (MRI) studies of insomnia and cognitive decline. Individuals with insomnia had reduced gray matter volume in the prefrontal cortex, cingulate gyrus, temporal lobe, and hippocampus, along with reduced integrity in the white matter, relative to controls.

These review findings suggest that insomnia and cognitive decline are bidirectionally related. “The bidirectional relationship between cognitive decline and insomnia underscores the critical importance of effective screening and intervention strategies in clinical practice,” the investigators concluded.

Study limitations include substantial heterogeneity across studies, potential recall bias, variability in the definitions of insomnia, and the inability to determine causality due to the high prevalence of cross-sectional studies.

This article originally appeared on Sleep Wake Advisor