Study Spotlight: Clarifying the Link Between Sleep Disturbance and Cognitive Decline

Most of us unfortunately are all too familiar with the short-term consequences of not getting a good night’s sleep. Less is known, however, about the long-term consequences of sleep disturbances, particularly their effect on brain health. A new study published in the September 2 edition of Neurology takes a closer look at symptoms of sleep disturbances—specifically snoring, sleepiness, and sleep duration—and their effect on cognition.1 Ahead, co-authors Alberto R. Ramos, MD, Assistant Professor of Clinical Neurology at University of Miami Miller School of Medicine, and Clinton B. Wright, MD, Professor of Neurology and Scientific Director of the Evelyn F. McKnight Brain Institute at the University of Miami School of Medicine, reflect on their findings and discuss future direction in sleep research.

What is currently known about the relationship of sleep disturbance and cognitive decline?

“Sleep disorders affect 50-70 million people in the US and particularly affect the older population,” note Dr. Ramos and Dr. Wright. “However, sleep disorders remain largely under recognized. This is coupled with the expected rise of Alzheimer’s disease and related dementias, with vast public health implications. Currently, there is no cure for dementias, highlighting the need for preventive strategies. Our study provides an opportunity to evaluate sleep as a potentially modifiable novel risk factor for cognitive decline and determine the cognitive domains that are affected by sleep disturbances,” they observe.

Can you talk a bit about the study design and results?

“The Northern Manhattan Study is a population-based observational study of risk factors for stroke and cognitive impairment. We measured self-reported sleep symptoms once and cognitive performance at two time points. We performed a two staged analysis of frequent snoring, daytime sleepiness and sleep duration across the cognitive domains of executive function, memory, language and processing speed, first evaluating the cross-sectional association between sleep disturbances and baseline cognitive function, followed by an evaluation of cognitive decline after approximately five years of follow-up.

“We hypothesized that snoring, daytime sleepiness and short and long sleep duration would be associated with cognitive decline in all domains,” they say. According to the findings, frequent snoring, severe daytime sleepiness and long sleep duration (more than nine hours of sleep) had strong associations with decline in executive function.

What can we glean from these results about sleep and cognition?

According to Dr. Wright and Dr. Ramos, cause and effect cannot be determined using this observational study design. Nevertheless, their findings highlight the growing appreciation of a role for sleep problems in cognitive decline. “Physicians may inquire about sleep disturbances in patients who present with cognitive complaints. Sleep symptoms such as snoring, daytime sleepiness and long sleep duration may be a surrogate for other sleep disorders (i.e. sleep apnea, circadian rhythm disorders) that can be treated,” they note. “The study provides a framework for further studies on sleep disorders and cognitive decline. We hope that future studies will target sleep and help develop strategies to identify at-risk populations and develop interventions to mitigate cognitive decline and dementia in a growing segment of the US population, older adults.” n

1. Ramos AR, et al. Neurology. 2016 Oct 4;87(14):1511-1516.