Associate Professor University of California, San Francisco South San Francisco, California, United States
Background: The gut microbiota is not fully understood as there are trillions of bacteria and hundreds of other species of fungi, viruses, yeasts, and parasites harbored in our GI system. Moreover, the composition of our gut microbiota is ever-changing due to influences from age, illness, diet, and other environmental factors. While studies in the adult population show that gut dysbiosis (an alteration in the homeostasis of bacterial composition) is associated with depression, there remains a lack of research examining the relationship of the gut microbiota to adolescent mental health. Objective: The purpose of this study was to assess whether microbial diversity and composition of the gut are associated with the severity of depressive symptoms. Design/Methods: Seventy-two adolescents 13 to 19 years of age were recruited from a community setting. The adolescents completed a demographic questionnaire and the Patient Health Questionnaire-9 (PHQ-9) and collected a stool sample. 16S rRNA gene sequencing was used to identify the diversity and abundance (composition) of microbial species. Confounders, such as sex, race, and body mass index were included in our final models. Permutational Multivariate Analysis of Variance was used to examine microbial diversity differences, and differential abundance analysis was performed to examine abundance differences among adolescents with self-reported depression, where a PHQ-9 cut-off score of ≥11 was used. Results: Bacterial diversity differed for those who reported PHQ-9 depression and those who did not (R² = 0.034, p = 0.047). Five bacterial species, including Bifidobacterium bifidum, showed significantly lower levels in adolescents with PHQ-9 depression (p < 0.001) compared to those without depression (Fig 1).
Conclusion(s): These findings highlight the significant role of the gut microbiota in mental health, indicating that differences in microbial composition may be associated with adolescent depression. Notably, protective bacteria like Bifidobacterium bifidum, commonly found in probiotics, were more abundant in adolescents who did not report depression. However, additional research is necessary to clarify the mechanisms underlying the relationships between the gut microbiome and mental health outcomes. Such research could lead to the identification of microbial markers and their genetic functions, ultimately guiding the development of targeted probiotic and therapeutic interventions for adolescent depression.
Fig 1. Depleted Taxa for Adolescents with PHQ-9 Depression Fig 1 Depleted Taxa Teen PHQ-9.pdf*Species N/A; there was not enough information to identify the species. **Effect sizes significant at p < 0.001.
