Cardiovascular Endurance Modifies the Link between Subjective Sleep Quality and Entorhinal Cortex Thickness in Younger Adults

INTRODUCTION: Poor sleep is linked to impaired cognitive function, cortical brain atrophy, and lower cortical thickness. Independently, higher cardiovascular endurance has neuroprotective effects. It remains in question, however, whether cardiovascular endurance moderates the relationship between sleep and brain health. The aims of this study included the following: 1) the association between subjective sleep quality and cognitive performance, hippocampus volume, and entorhinal cortex (EC) thickness, and 2) the moderating effects of cardiovascular endurance on the associations of sleep quality with cognitive and magnetic resonance imaging measures in healthy younger adults. METHODS: A total of 1095 younger adults (28.8 ± 3.6 yr) from the Human Connectome Project were included in the analyses. The 2-min walk test was used as a proxy of cardiovascular endurance. Self-reported sleep quality was measured using the Pittsburgh Sleep Quality Index. Composite cognitive tests were used to assess global cognition, and T1-weighted structural magnetic resonance imaging data (obtained using Siemens 3T scanner) was used to assess hippocampus volume and EC thickness. Linear regression was used to examine the moderating effects of fitness on the relationships between sleep and each of these neurocognitive outcomes after controlling for age, sex, and education year. RESULTS: Poorer sleep quality was associated with both a lower crystalized intelligence score (B = -0.198, P = 0.034) and lower EC thickness (B = -0.013, P = 0.003). With greater 2-min walk test score, the association between greater Pittsburgh Sleep Quality Index score and lower EC thickness was attenuated (B = 0.0008, P = 0.028). CONCLUSIONS: Higher cardiovascular endurance may mitigate the relationship between poorer subjective sleep quality and lower EC thickness. Future longitudinal studies should examine the interactive effects of sleep and fitness on brain health among older and more vulnerable populations.