Habitual daytime napping tied to larger brain volume and improved cognitive health

UK: A recent study published in Sleep Health has shed light on the association between daytime napping, cognitive function, and brain volume. The

Researchers at University College London, United Kingdom, and the University of the Republic of Uruguay, Montevideo, found a modest causal link between habitual napping and larger total brain volume, a surrogate marker for better cognitive health. 

The study utilized data from the UK Biobank, including information from a large sample of participants with a mean age of 57. The researchers employed Mendelian randomization, a method that utilizes genetic variants as instrumental variables, to investigate the relationship between habitual daytime napping and cognition and brain structure.

Using 92 independent genetic variants (single-nucleotide polymorphisms, SNPs) previously associated with daytime napping, the researchers analyzed the outcomes of total brain volume, hippocampal volume, reaction time, and visual memory. The Mendelian randomization analysis, which accounted for potential confounding factors, revealed a significant association between habitual daytime napping and larger total brain volume. Specifically, the study found an increase of 15.8 cubic cm in total brain volume among individuals who napped more frequently.

The association between daytime napping and other cognitive outcomes and brain structure was also explored in additional analyses using different sets of genetic variants. The results remained consistent, supporting the initial findings. Importantly, the researchers found no evidence of horizontal pleiotropy, indicating that the observed effects were unlikely to be influenced by other genetic factors.

● Utilising Mendelian randomization has discovered a link between regular daytime napping and increased total brain volume. The analysis revealed an unstandardized effect size (ß) of 15.80 cm3, with a 95% confidence interval (CI) ranging from 0.25 to 31.34.

● No significant associations were found between daytime napping and hippocampal volume (ß = -0.03 cm3; 95% CI = -0.13 to 0.06), reaction time (expß = 1.01; 95% CI = 1.00 to 1.03), or visual memory (expß = 0.99; 95% CI = 0.94 to 1.05).

● The researchers conducted additional analyses using different sets of genetic variants to ensure the robustness of their findings. These supplementary analyses, which involved 47 single-nucleotide polymorphisms (SNPs) adjusted for excessive daytime sleepiness, 86 SNPs excluding sleep apnea, and 17 SNPs with no sample overlap with the UK Biobank, largely confirmed the study's main findings.

● There was no evidence of horizontal pleiotropy, which suggests that confounding factors did not influence the observed associations.

The findings contribute to the growing body of evidence regarding the potential advantages of incorporating a short nap into daily routines. As future research continues to explore the relationships between napping and other cognitive and brain-related outcomes, these findings may have implications for interventions aimed at promoting healthy brain aging and maintaining cognitive function.

Reference:

Paz, V., Dashti, H. S., & Garfield, V. (2023). Is there an association between daytime napping, cognitive function, and brain volume? A Mendelian randomization study in the UK Biobank. Sleep Health. https://doi.org/10.1016/j.sleh.2023.05.002