Associations between sleep traits and social isolation: observational and bidirectional Mendelian randomization study.

Social isolation has been found associated with multiple sleep traits in conventional observational studies. However, whether this association is causal and if so, its direction, is uncertain. We analyzed the association between social isolation and multiple sleep traits in 30,430 participants from the Guangzhou Biobank Cohort Study (GBCS). In bidirectional Mendelian randomization, we used 6, 17 and 11 single nucleotide polymorphisms (SNPs) associated with attendance at sports club/gym, religious group and pub/social club from the UK Biobank (n=452,302), respectively, and 152 SNPs associated with insomnia from the combination of UK Biobank and 23andme (n=1,331,010). Observationally in GBCS, insomnia (yes/no) (beta=0.12, 95% confidence interval (CI) 0.10-0.16) and poor sleep quality (yes/no) (beta=0.12, CI:0.08-0.15), but not sleep duration and chronotype, were associated with higher social isolation score (severe social isolation). In bidirectional MR, genetically predicted insomnia decreases the odds of attendance at sports club/gym (beta=0.98, CI: 0.98-0.99) and religious group (beta=0.99, CI: 0.98-0.99), but not pub/social club. However, these three types of social activity were not associated with insomnia. Our results support the causal effects of insomnia on social activity. Further clinical investigations into the utility of insomnia treatment in alleviating social isolation are needed.