Objective: The aim of the study was to address the possibility that microbial exchange between individuals in close contact may introduce a hidden bias due to differing microbiota phenotypes.

Materials and Methods: A random sample of 296 spouses experiencing insomnia and 296 spouses experiencing hypersomnia was selected from a total of 1,740 couples initially enrolled in previously conducted trials. Overall, 296 otherwise healthy spouses of individuals with insomnia were compared with 296 healthy spouses of individuals with hypersomnia in terms of microbiota phenotypes. Microbiota phenotypes were extracted from the existing literature and further categorized into different phenotypes. The microbiota phenotypes in otherwise healthy spouses were evaluated, and differences between groups were assessed using Chi-square tests.

Results: There were significant differences (p-value < 0.01) in the occurrence of microbiota phenotypes between the two groups of otherwise healthy spouses of individuals with (i) insomnia and (ii) individuals with hypersomnia in terms of microbiota phenotypes.

Conclusions: We recommend that microbiota research incorporates the baseline characteristics of peers, spouses, and immediate family members. This short communication holds substantial therapeutic and pharmacological significance for various types of clinical trials, as well as for the fields of family medicine and personalized medicine.