Sleep, hippocampal volume, and cognition in adults over 90 years old

Several lines of research support associations between sleep and cognition in older adults. However, there is a paucity of data regarding sleep and cognition in nonagenarians and centenarians.

The current study examined self-reported sleep quantity and sleep quality in relation to hippocampal volume and cognition in adults aged 90 and older.

A total of 144 participants of The 90+ Study completed The Medical Outcomes Study sleep questionnaire. Participants reported subjective sleep duration in hours and three sleep quality factors: sleep problems, adequacy, and somnolence. Neuropsychological assessments of memory, global cognition, language, and executive function were completed, on average, 61 days from the questionnaire. Hippocampal volume on 3 T MRI, adjusted for intracranial volume, was obtained in 82 participants. We performed multiple linear regressions, controlling for age, sex, education, sleep medication, and depression, to examine sleep characteristics in relation to hippocampal volume and cognitive performance in all the subjects and then stratified by cognition.

Sleep duration > 8 h was associated with lower scores in tests of global cognition, memory, and executive function compared to sleep duration of 7-8 h when collapsing across cognitive status, but only with memory in cognitively impaired subjects, and not in cognitively normal subjects.

Long-sleep duration is associated with poorer global cognition, memory, and executive function in the oldest-old, and is only associated with memory in cognitively impaired oldest-old. Additional research is necessary to determine if sleep duration is a risk factor or a result of poor cognition in advanced age.