BOSTON—Quality of sleep is directly correlated with cognitive scores among middle-aged adults, according to research presented at the 2013 Alzheimer’s Association International Conference. Measures of memory and executive function were associated with better self-reported ratings of sleep quality.
Better sleep also is associated with better status on measures of vascular, metabolic, and psychologic health, said Rebecca L. Koscik, PhD, Associate Scientist at the Wisconsin Alzheimer’s Institute in Madison. Good results on various health markers are associated with better cognition. Improving sleep quality in middle age may reduce the risk of cognitive decline, but longitudinal evaluation of these variables is needed to determine causal patterns, she added.
Analyzing Data From a Registry for Alzheimer’s Disease Prevention
To analyze the relationships between measures of sleep, depression, vascular and metabolic health, and cognition, Dr. Koscik and colleagues analyzed data for 257 participants in the Wisconsin Registry for Alzheimer’s Prevention. Subjects’ baseline age was 54. More than 70% of the population had a family history of Alzheimer’s disease, but no patients had a neurologic condition.
Participants’ sleep was evaluated with the Sleep Scale from the Medical Outcomes Study (MOS) and the Epworth Sleepiness Scale. The investigators coded all sleep variables so that higher numbers indicated better sleep. Tests such as the Rey Auditory Verbal Learning Test and the Wechsler Adult Intelligence Scale assessed patients’ cognitive abilities. The researchers also administered the Center for Epidemiologic Studies Depression (CES-D) Scale and evaluated concurrent metabolic and vascular measures such as BMI, HDL cholesterol, and insulin resistance.
Somnolence Was Associated with Cognitive and Metabolic Outcomes
Cognitive, depression, vascular, and metabolic scores correlated most significantly with the Somnolence Scale, which is part of the MOS Sleep Scale. The Spearman correlation between the Somnolence Scale and CES-D score was –0.289, indicating that less daytime drowsiness was associated with fewer depressive symptoms in this group. Patients with less somnolence were also more likely to have lower BMI, lower waist-to-hip ratio, higher levels of HDL cholesterol, and lower insulin resistance. These results indicate that a pattern of better sleep is associated with better status on measures of vascular and metabolic health. The researchers observed similar relationships between scores on the Snoring Scale of the MOS Sleep Scale and these vascular and metabolic variables. Excessive daytime sleepiness, as measured with the Epworth Scale, was associated with lower performance on measures of memory.
The investigators also observed that greater sleepiness was associated with higher levels of inflammation, as indicated by homocysteine and lower levels of HDL cholesterol. In contrast, higher homocysteine values were correlated with lower scores on verbal learning and memory tests, while higher levels of HDL cholesterol were correlated with higher scores on verbal learning and memory tests. “Future research will include longitudinal evaluation of how sleep, metabolism, and vascular health contribute to cognitive aging trajectories,” Dr. Koscik told Neurology Reviews.
—Erik Greb
Senior Associate Editor