SEATTLE—Sleep disturbances are associated with worse cognitive performance, particularly within the domain of executive function, according to data presented at the 29th Annual Meeting of the Associated Professional Sleep Societies. The results suggest that disrupted sleep may be a modifiable risk factor for cognitive impairment. Together with future research, these data may help neurologists understand which cognitive functions are more affected by sleep disturbances and develop targeted treatment studies to improve cognitive function in the elderly.

Previous studies have indicated that sleep disturbances may increase the risk of cognitive impairment and dementia. Alberto R. Ramos, MD, Assistant Professor of Clinical Neurology at the University of Miami Miller School of Medicine, and colleagues performed a cross-sectional evaluation of the association between sleep disturbances and cognitive performance in several cognitive domains. The researchers’ secondary aim was to evaluate the longitudinal association between self-reported sleep disturbances and cognitive decline.

Researchers Collected Neuropsychologic and Sleep Variables
The investigators examined data from the Northern Manhattan Study (NOMAS), an ongoing population-based observational study designed to evaluate the risk factors for stroke in a multiethnic cohort. The initial sample included 3,200 participants. The majority of participants was of Hispanic/Latino background, and the sample included approximately equal numbers of non-Hispanic whites and non-Hispanic blacks.

Dr. Ramos and colleagues focused on the Northern Manhattan Study’s cognitive decline substudy. Participants underwent initial neuropsychologic testing from 2002 through 2006 and follow-up neuropsychologic testing from 2010 through 2014. The investigators obtained self-reported sleep variables in 2002 and 2003.

The outcomes for Dr. Ramos’s analysis were executive function, episodic memory, processing speed, and semantic memory. The independent variables included frequent snoring (ie, self-reported snoring more than three times per week) and modified Epworth Sleepiness Scale (ESS). Based on ESS scores, participants were categorized as having no dozing, mild dozing, or severe dozing. The researchers also collected information about sleep duration, which was categorized as short sleep (ie, less than six hours), average sleep (ie, from six to nine hours), and long sleep (ie, more than nine hours).

The study’s main covariate was a composite score that incorporated the NOMAS global vascular risk score, which was intended to define the 10-year risk of stroke or heart attack in this sample. The composite score also incorporated sociodemographic variables such as age, ethnicity, and gender, as well as traditional vascular risk factors such as blood pressure, fasting glucose level, and smoking status. The researchers added other risk factors such as moderate alcohol consumption and moderate-to-heavy physical activity to the composite score.

In their statistical analysis, Dr. Ramos’s group performed a cross-sectional evaluation of participants’ sleep disturbances and the z scores for each cognitive domain. They next calculated age- and education-adjusted z scores for cognitive decline, further adjusting the data for the global vascular risk scores and time variables.

Long Sleep Durations Harmed Cognitive Performance
The mean age in Dr. Ramos’s sample was 63, and 62% of the population was female. Less than half of participants had a high-school education, and about half of participants had Medicaid or no insurance. The majority of the sample (67%) was Hispanic/Latino.

When Dr. Ramos and colleagues examined the population’s independent variables, they found that 29% had frequent snoring. Approximately 8% of participants had severe dozing, and 48% had mild dozing. About 27% of the sample had short sleep duration, and 9% had long sleep duration. Participants’ global vascular risk score was 8.1, which indicated a moderate-to-high risk of stroke or heart attack within 10 years.

Compared with people who did not snore, patients who snored had worse cognitive scores in executive function, semantic memory, and processing speed. People with long sleep duration had worse scores in all cognitive domains, compared with people with short or average sleep duration. Participants who reported severe dozing performed worse on all cognitive functions at baseline, compared with people with no dozing or mild dozing.

When the researchers examined cognitive scores, they found that participants who snored had worse executive function and mean semantic memory, compared with people who did not snore. Participants who snored did not have worse episodic memory or delayed recall, however. In addition, people with long sleep duration had worse executive function, compared with people with short or average sleep duration. Participants with severe dozing had worse executive function, semantic memory, and processing speed than participants with no or mild dozing. Episodic memory, however, was not affected in participants with severe dozing.

A data analysis using fully adjusted models indicated that participants with snoring, severe dozing, and long sleep duration had larger declines in executive function. The investigators observed no differences for episodic memory, processing speed, or semantic memory.

—Erik Greb

Sleep Disturbances May Degrade Executive Function