Is there an association between daytime napping and cognitive function? A Mendelian randomisation study in the UK Biobank

Abstract

AbstractBackgroundDaytime napping has been associated with cognitive function in observational studies. However, it remains elusive whether napping could be beneficial or detrimental for cognition and whether these associations are causal.MethodsUsing Mendelian randomisation (MR), we studied the relationship between daytime napping and cognitive outcomes. Data were from UK Biobank (n= 378,932; mean age= 57 years). Our exposure (daytime napping) was instrumented using 92 genome-wide, independent genetic variants and our cognitive outcomes were reaction time and visual memory. Inverse-variance weighted MR was implemented, with sensitivity analyses including MR-Egger and the Weighted Median Estimator for horizontal pleiotropy. We also tested different daytime napping instruments (47 SNPs, 86 SNPs and 17 SNPs) to ensure the robustness of our results.ResultsNo associations were found between daytime napping and reaction time (expß=1.01, 95%CI=1.00; 1.03), or visual memory (expß=0.99, 95%CI=0.94; 1.05). MR-Egger and Weighted Median Estimator approaches showed no evidence of horizontal pleiotropy. Additional analyses with 47 SNPs (adjusted for excessive daytime sleepiness), 86 SNPs (excluding sleep apnoea) and 17 SNPs (no sample overlap with UKB) also showed no associations with reaction time or visual memory.ConclusionsOverall, we observed no evidence of a causal association between habitual daytime napping and reaction time and visual memory. Future studies should focus on the associations between napping and other cognitive outcomes.