In their work, the researchers applied a Mendelian randomization method, comparing 92 genetic variants that determine the predisposition to daytime sleep with MRI results and cognitive tests. The results were published in the journal Sleep Health: Journal of the National Sleep Foundation.
In a subsample of 35,000 individuals who underwent MRI, it was found that people with a genetic predisposition to regular daytime napping had an average brain volume that was 15.8 cubic centimeters larger. According to the authors' estimates, this may correspond to 2.5-6.5 years of slower age-related brain volume decline. This means that those who nap more frequently during the day may maintain a larger brain volume in adulthood.
However, the study did not find a link between daytime sleep and the size of the hippocampus, reaction time, or visual memory, indicating that daytime napping does not have a direct impact on cognitive functions.
The authors emphasize that while there is a connection between daytime sleep and brain volume, it is modest and requires further investigation for a complete understanding of the mechanisms.
