Understanding Short Sleep Duration’s Impact in Insomnia

Julio J. Fernandez-Mendoza, PhD

Recently, Julio J. Fernandez-Mendoza, PhD, and colleagues published their findings from an analysis of the Penn State Adult Cohort which implied that insomnia, when accompanied by objective short sleep duration, can lead to an increased prevalence of cognitive impairment, particularly as it relates to cardiometabolic health.

All told, the group observed that those who reported poor sleep or chronic insomnia who slept for fewer than 6 hours were twice as likely to have cognitive impairment and possible vascular cognitive impairment compared with those who slept more than 6 hours. The analysis included 1524 adults (mean age, 48.9 years [±13.4]), and self-reported sleep difficulty was defined as normal sleep (n = 899), poor sleep (n = 453), and chronic insomnia (n = 172). Objective short sleep duration was defined as less than 6 hours of sleep, which was based on in-lab, 8-hour polysomnography. Cognitive impairment (n = 155) and possible vascular cognitive impairment (n = 122) were determined with a comprehensive neuropsychological battery.

The odds ratios (ORs) for cognitive impairment for those with poor sleep and insomnia with objectively short sleep duration were 2.06 (95% CL, 1.15–3.66) and 2.18 (95% CL, 1.07–4.47), respectively. Likewise, the ORs for possible vascular cognitive impairment for those with poor sleep and insomnia who slept fewer than 6 hours were 1.94 (95% CL, 1.01–3.75) and 2.33 (95% CL, 1.07–5.06), respectively.

To find out more about the data and their clinical implications, NeurologyLive reached out to Fernandez-Mendoza, who is a clinician-scientist at Penn State Hershey Sleep Research & Treatment Center of Penn State Health.

NeurologyLive: How do these data translate to clinical practice and of what do they inform clinicians?

Julio J. Fernandez-Mendoza, PhD: These data are among the first to indicate that patients who complain of insomnia and who sleep objectively short in the lab have a higher prevalence of mild cognitive impairment, particularly that associated with cardiometabolic risk factors.

From a practice standpoint, patients with insomnia who have cardiometabolic risk factors should be objectively evaluated for their nighttime sleep and cognition, and not just evaluated by self-reports. Conversely, patients with mild cognitive impairment presenting at neurology clinics who complain of insomnia should undergo a sleep study not only to examine the potential contribution of sleep apnea and other sleep disorders but also to identify this more severe form of insomnia that may require specific treatment approaches.

From a treatment standpoint, these data indicate that patients with insomnia, cardiometabolic risk factors, and mild cognitive impairment may require more targeted treatments, such as the combination of cognitive-behavioral and pharmacological therapies when addressing these clustering of highly impairing conditions.

Were any of these findings surprising or unexpected in any way?

A somewhat unexpected finding was that those with poor sleep who slept objectively short in the lab had a similar degree of association with mild cognitive impairment as did those with chronic insomnia who slept short in the lab. Usually, these poor sleepers, who are individuals with insomnia symptoms who have not yet developed chronic insomnia, show a relatively lower degree of association compared to those the chronic disorder. This suggests that when it pertains to cognitive impairment even poor sleep, and not only chronic insomnia, coupled with objective short sleep is a meaningful risk factor or associated clinical feature that should be paid attention to.

What still needs to be clarified in this area of research?

We need longitudinal studies that follow large groups of good sleeping and poor sleeping young and middle-aged adults for enough years to ascertain whether insomnia with objective short sleep duration is a predictor of cognitive decline and future development of cognitive impairment and dementia. We also need these studies to include neuroimaging and biomarker data so that the underlying etiology of the cognitive impairment observed in individuals with this type of more biologically severe insomnia can be truly disentangled.

Transcript edited for clarity.

REFERENCE
Fernandez-Mendoza J, He F, Puzino K, et al. Insomnia with objective short sleep duration is associated with cognitive impairment: a first look at cardiometabolic contributors to brain health. Sleep. Published online September 24, 2020. doi: 10.1093/sleep/zsaa150