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Sleep disorders may increase cognitive decline

Individuals with sleep disordered breathing are more likely to have diminished cognition, including poorer attention, processing speed and memory, especially those who are genetically susceptible to Alzheimer’s disease, according to findings published in the Annals of the American Thoracic Society.

“Sleep-disordered breathing is a highly prevalent condition that is characterized by repeated pauses (apneas or hypopneas) in breathing during sleep,” Dayna A. Johnson, PhD, MPH, MS, from the division of sleep and circadian disorders at Brigham and Women’s Hospital, and colleagues wrote. “[Sleep-disordered breathing] is particularly prevalent among elderly populations, older men and racial minority groups (African American, Hispanic, Asian). Individuals with [sleep-disordered breathing] commonly report problems with cognition and may be at increased risk for dementia.”

In a related press release, Johnson said, “Previous studies have shown inconsistent findings between sleep-disordered breathing and cognition, which may be due to the different tests used.”

Johnson and colleagues investigated how indicators of sleep-disordered breathing affect cognitive function and if this association was modified by the apolipoprotein epsilon-4 allele. They studied a diverse group of patients from the Multi-Ethnic Study of Atherosclerosis who completed standardized sleep questions and a series of cognitions tests and underwent Type 2 in-home polysomnography which assessed overnight hypoxemia — oxygen saturation below 90% —and apnea-hypopnea index. An apnea-hypopnea index of more than 15 was used to defined sleep disordered breathing. Epworth Sleepiness Scale score which quantified daytime sleepiness, as well as sleep apnea syndrome, defined as an apnea-hypopnea index of five or greater and an Epworth Sleepiness Scale score of more than ten, were also measured. In addition, the Cognitive Abilities Screening Instrument, Digit Symbol Coding Test and Digit Span Tests Forward and Backward were used to analyze cognition. The analysis was adjusted for race, age, BMI, education level, smoking status, hypertension, diabetes, benzodiazepine use and depressive symptoms.

Among the participants (n = 1,752; mean age, 68.1 years; median apnea hypopnea index, 9; mean Epworth Sleepiness Scale score, 6), sleep apnea syndrome was present in 9.7% and at least one copy of the apolipoprotein epsilon-4 allele was present in 26.8%. Analysis showed that increased overnight hypoxemia and daytime sleepiness were related to poorer attention and memory (beta = –0.12 [standard error: 0.06] and beta = –0.13 [standard error: 0.06], respectively; P < .05). Sleep apnea syndrome was also linked to poorer attention. More daytime sleepiness and sleep apnea syndrome were associated with slower cognitive processing. These associations were strongest in participants with the apolipoprotein epsilon-4 allele.

The researchers noted that although the effect estimates were small, they were similar to those for several other individual dementia risk factors.

“Our study provides further evidence that sleep-disordered breathing negatively affects attention, processing speed and memory, which are robust predictors of cognitive decline,” Susan Redline, MD, MPH, senior study author and Peter C. Farrell Professor of Sleep Medicine at Harvard Medical School, said in the release.

“Given the lack of effective treatment for Alzheimer’s disease, our results support the potential for sleep-disordered breathing screening and treatment as part of a strategy to reduce dementia risk,” especially for individuals who carry the apolipoprotein epsilon-4 allele, she added.

Similarly, a previous study also found that poorer sleep may indicate Alzheimer’s disease risk. – by Alaina Tedesco

Disclosure: The researchers report no relevant financial disclosures.