Evolution of oral microbiota during adolescence – a longitudinal study from Finland

Background: Obesity is increasing globally among children and adolescents. Saliva microbiota is being studied as an alternative to gut microbiota due to its links to diseases, including obesity, though findings are inconsistent. We conducted a follow-up study to examine changes in saliva microbiota composition among adolescents with stable weight compared to those with increased weight. Methods: We analyzed saliva samples from 440 adolescents in the Finnish Health in Teens cohort at ages 11.7 and 14.2, using 16S rRNA gene sequencing. Adolescents were grouped by BMI based on International Obesity Task Force criteria. We examined differences in alpha diversity, beta diversity, and composition between children who stayed in the same BMI category and those who increased their BMI. Results: The core microbiota composition varied between two timepoints, with significant alterations in adolescents with persistent overweight or obesity. Specifically, the genera Haemophilus and Neisseria increased in these individuals. The microbiota remained more stable in adolescents who were previously normal weight, even if they gained weight. Conclusions : Our findings suggest that saliva microbiota evolves during adolescence. The changes in saliva microbiome with time were more pronounced in those with persistent overweight/obesity, pointing towards chronic, low-grade inflammation and metabolic dysregulation.