Sleep duration over 28 years, cognition, gray matter volume, and white matter microstructure.
It was hypothesized that consistently meeting sleep guidelines (i.e. sleeping at least 7 hours per night) would be associated with improved cognition, increased gray matter volumes and improved white matter microstructure (increased FA and reduced
RD) compared with consistently missing the guidelines, or transitioning in and out of the guidelines over time. However, such hypotheses were not supported by the results of this study, as it was found that sleep duration remained relatively stable over 28 years and that there was no evidence of differences in cognition or MRI findings between sleep trajectory groups.