Researchers of a recent study investigated the causal relationship between daytime napping and cognitive function as well as brain structure using a method called Mendelian randomization. The outcomes of interest were total brain volume, hippocampal volume, reaction time, and visual memory. The results showed that habitual daytime napping was associated with larger total brain volume but not with hippocampal volume, reaction time, or visual memory. Additional analyses using different sets of single-nucleotide polymorphisms, including those adjusted for excessive daytime sleepiness and excluding sleep apnea, yielded similar findings. No evidence of horizontal pleiotropy, a potential source of bias, was observed.

In conclusion, this study suggests a modest causal association between habitual daytime napping and larger total brain volume.

Reference: Paz V, Dashti HS, Garfield V. Is there an association between daytime napping, cognitive function, and brain volume? A Mendelian randomization study in the UK Biobank [published online ahead of print, 2023 Jun 12]. Sleep Health. 2023;S2352-7218(23)00089-X. doi:10.1016/j.sleh.2023.05.002

Link: https://www.sciencedirect.com/science/article/pii/S235272182300089X