Poor Sleep Linked With Future Cognitive Decline, Clinicians Should Target Intervention

In this exclusive Q&A, Anders Behrens MD, PhD, a neurologist practicing at Blekinge hospital in Karlskrona, Sweden, spoke with Neurology Learning Network about the results of his recent study “Sleep Disturbance Predicts Worse Cognitive Performance in Subsequent Years: A Longitudinal Population-Based Cohort Study,” recently published in the journal Archive of Gerontology and Geriatrics Research.

Given the growing evidence that sleep is important to brain health, particularly with the newly discovered glymphatic system, Dr Behrens and colleagues aimed to explain the link between sleep and future cognition in the aging brain. Dr Behrens and co-authors’ findings provide much-needed insight as clinicians treat patients presenting symptoms of sleep disorders who may be at risk for future decline. "For clinical practice we think that one should at least not neglect sleep as a factor for physical and mental health," says Dr Behrens who discusses the study's methods, key and surprising findings, practical implications, and impact on future research.

Meagan Thistle, Neurology Learning Network: What led you and your colleagues to investigate subjective measures of sleep duration and sleep disturbance with future cognitive decline?

Anders Behrens, MD, PhD: There is a growing realization of the importance of sleep in the field of brain health. The discovery of the glymphatic system provides a plausible explanation for the link between sleep and future cognition. Subjective measures of sleep are easily available and can indicate modifiable factors affecting sleep (and potentially future cognition), which was our primary motivator for conducting the study.

Thistle: Please briefly describe the study methods and participants.

Dr Behrens: The study is based on a population-based cohort of 60, 66, 72, and 78 year-olds. The participants were examined at baseline with a comprehensive battery of surveys, blood samples, cognitive tests (MMSE and clock drawing test), and a sleep scale. The cohort was longitudinally followed with the same tests every 6 years until 78 years old. The association between sleep disturbance and cognitive variables was assessed, both cross-sectionally for each age cohort and longitudinally. 

Thistle: Please briefly describe the most significant finding(s).

Dr Behrens: Sleep disturbance was associated with impaired cognitive test performance both cross-sectionally and longitudinally for the 60-year-olds, but not for any of the other age cohorts. The items of the sleep scale most predictive of later life cognition regarded nightly awakenings, pain and itching and long (≥2 hours) daytime naps. Long sleep (≥9 hours per night) was predictive of future worse cognitive performance.

Thistle: Your cross-sectional analysis found an association between sleep disturbance and cognition only in the 60-year-old participant group. Why do you think that is, and how can clinicians utilize this information in their practice?

Dr Behrens: There may be many explanations for this. The 60-year-olds are mostly still working and along with that time restricted in their sleep time, and they are also affected by the stress of working life.  We found that the proportion of poor sleepers decreased from 60 to 66-year old’s, which we hypnotize is a retirement effect. We also believe that the older cohorts there are increasingly other factors than sleep affecting cognition, giving less power to detect an association from a single factor.

For clinical practice we think that one should at least not neglect sleep as a factor for physical and mental health. We believe that increased awareness of both for sleep disorders but also promoting sleep health for the general population (sleep hygiene and sleep environmental factors) will have impact on the life of our patients. 

Thistle: Were any study outcomes or findings different than you expected?

Dr Behrens: The literature on subjective measures of sleep disturbance has been mixed but makes more sense after our study. A pattern where studies on older subjects, and shorter follow up times give less significant results. 

Thistle: What are the practical implications of your findings for clinicians treating patients with sleep disturbances?

We believe that the main practical implication is not to neglect sleep health and sleep disorders in our patients. The results indicate some specific areas, daytime naps, pain and itching, waking during the night and long sleep during the night, that need further attention and research and might be a target for intervention. 

Thistle: Are you conducting further research in this area, and do you feel that future studies are needed?

Dr Behrens: Yes and yes. We intend to follow up on the findings from this study. Though previously described in the literature, it is not clear why sleeping long hours and taking daily long naps predict future cognitive impairment. We suspect that more objective markers of sleep quality might shed light on this. The development of home EEG monitoring with automatic assessment of sleep biomarkers seems like a promising tool in this regard.

Also, it is clear that the MMSE is of limited sensitivity when doing population-based research where most of the participants scored max or close to the maximum score. We developed an automated cognitive test (CoGNIT) for tablet computers which we currently evaluate. We believe that a test with less pronounced ceiling effect may give more power to our research. 

Thistle: Any final thoughts pertaining to this research topic that you would like to share with the NLN audience?

Sleep well!

Dr Behrens is a neurologist working at the Blekinge hospital in Karlskrona, Sweden, also doing part time research and work as a senior lecturer at the Blekinge institute of Technology.