BOSTON—Compared with intermediate sleep duration, shorter sleep is associated with greater brain atrophy among community-dwelling older adults, according to a study presented at the 31st Annual Meeting of the Associated Professional Sleep Societies. Sleep duration appears to have no association with hippocampal volume, however.
More than 80% of older adults have sleep complaints, and research indicating an association between disturbed sleep and poor cognitive outcomes is accumulating. Sleep could be a crucial modifiable risk factor for cognitive outcomes, but few studies have examined the association between nonrespiratory sleep measures and brain volume, said Adam Spira, PhD, Associate Professor of Mental Health at Johns Hopkins Bloomberg School of Public Health in Baltimore.
Adam Spira, PhD
Participants Underwent MRI and Actigraphy
Dr. Spira and his colleagues at the National Institute on Aging Intramural Research Program and Johns Hopkins University studied adults without dementia enrolled in the ongoing Baltimore Longitudinal Study of Aging. To be eligible for the study, participants could not have cognitive impairment, functional limitations, or chronic medical conditions besides controlled hypertension.
Dr. Spira and colleagues examined the 183 participants for whom wrist actigraphy and MRI data from the same study visit were available. The sample’s mean age was 75. About 57% of the sample was female, and 28% were racial or ethnic minorities (mostly African American). Approximately 84% of the sample had 16 or more years of education.
Participants completed an average of 6.8 nights of actigraphy. The actigraph unit was worn on the nondominant wrist. The study’s primary actigraphy variables were total sleep time (TST), wake after sleep onset (WASO), and average wake bout length. Participants also underwent 3-T MRI, and the researchers’ main imaging variables were ventricular volume and hippocampal volume. Dr. Spira and colleagues adjusted their analyses for age, sex, education, race, depressive symptomatology, and the log of the intracranial volume.
Links Between Sleep and Brain Volumes
The population’s mean TST was 6.6 hours, and the investigators divided the TST data into tertiles. The mean TST for tertile 1 was 5.4 hours, the mean TST for tertile 2 was 6.6 hours, and the mean TST for tertile 3 was 7.7 hours. Mean WASO was 53 minutes, and mean wake bout length was 2.5 minutes.
Dr. Spira’s group found a statistically significant 0.17-unit increase in ventricular volume in tertile 1, compared with tertile 2. They also found a 0.12-unit increase in ventricular volume in tertile 3, compared with tertile 2, but the difference did not reach statistical significance. WASO was not associated with ventricular volume, but the investigators found a statistically significant 0.06-unit increase in ventricular volume for every standard deviation increase in average wake bout length.
There was no significant association between TST and hippocampal volume. Every standard deviation increase in WASO, however, was associated with decrease in hippocampal volume that was not statistically significant. Wake bout length was not associated with hippocampal volume.
Because it is a cross sectional study, the researchers cannot examine the temporal associations that would support the possibility of a causal effect of sleep on brain atrophy, said Dr. Spira. “It could also be that brain atrophy is linked to disturbed sleep,” he added. The investigators did not screen participants for sleep apnea or adjust the data for BMI.
The findings are consistent, however, with longitudinal results of studies with self-report measures of sleep duration or quality, and with cross sectional associations between actigraphic fragmentation indices and lower brain volumes.
“Longitudinal studies with larger samples are needed,” said Dr. Spira. “Ultimately, trials will be needed to examine the effects of optimizing sleep on cognitive and neuroimaging outcomes.”
—Erik Greb
Suggested Reading
Branger P, Arenaza-Urquijo EM, Tomadesso C, et al. Relationships between sleep quality and brain volume, metabolism, and amyloid deposition in late adulthood. Neurobiol Aging. 2016;41:107-114.
Koo DL, Shin JH, Lim JS, et al. Changes in subcortical shape and cognitive function in patients with chronic insomnia. Sleep Med. 2017;35:23-26.