Effect of Probiotics on Stress Scores, Cortisol Levels, and Immune Functions in Moderately Stressed Adolescents and Young Adults: Results of a Feasibility Clinical Study

Background: Stress can negatively affect immune system functions by regulating cytokine production. The purpose of this feasibility study was to investigate the effects of a probiotic supplement on stress, cortisol levels, and the immune functions of moderately stressed adolescents and young adults. Methods: A randomized, single-blind clinical trial was conducted at Primary Children’s Hospital, Utah. Eighty-seven moderately stressed (Perceived Stress Score, PSS, 14–26) volunteers (12–20 years old) completed the study. Participants took either a probiotic blend containing three Lactobacillaceae strains or placebo capsules for 12 weeks. Participants’ PSSs were evaluated following office visits at baseline, and after 8 and 12 weeks of supplementation. Participants’ collected salivary samples were analyzed for cortisol, secretory IgA, and a panel of cytokines (IL-1β, IL-6, IL-8, TNF-α, and IL-10). Results: Both cohorts showed decreases in PSS and increases in morning salivary cortisol levels; the difference between cohorts was not statistically significant. Probiotics slowed the increase in cortisol levels and had a beneficial effect on cytokine production, with a statistically significant reduction in IL-1β levels compared to placebo (p = 0.03–0.004). A statistically significant, weak positive correlation between cortisol levels and IL-1β (r = 0.16, p = 0.015) has been observed. Conclusions: This study’s results suggest that probiotic supplementation may influence cortisol dynamics and cytokine responses in moderately stressed adolescents and young adults, with IL-1β showing the most consistent between-cohort difference. These findings support further investigation of probiotic supplementation in more rigorously designed trials that account for the types of stress experienced by participants in early life and during the study.