Effects of Bifidobacterium longum 1714 on low mood and related symptoms: A randomized, double-blind, placebo-controlled trial.

Psychobiotics have been suggested as an alternative or adjunctive intervention for depressive symptoms. Bifidobacterium longum (B. longum) 1714 has previously been shown to influence stress response and sleep quality. This double-blind, placebo-controlled trial investigated whether B. longum 1714 (1 × 10¹⁰ colony-forming units/day) affects severity of depressive symptoms in 168 adults (aged 18-70) with mild to moderate depression over 8 weeks. The primary outcome was the change in Beck's Depression Inventory-II scores. Secondary outcomes included changes in sleep quality and mental wellness, measured by the Pittsburgh Sleep Quality Index, Patient Health Questionnaire-9, Short Form Health Survey-36, Cohen's Perceived Stress Scale, Visual Analogue Scales for fatigue and energy, and the adapted Global Clinical Impression. Changes in Beck's Depression Inventory-II scores from baseline were not significantly different between intervention and placebo at Week 4 (-0.303, 95% CI [-1.957, 1.35]; p = .718) or Week 8 (-1.432, 95% CI [-3.30, 0.44]; p = .132). However, at Week 4, decreases in both Pittsburgh Sleep Quality Index total score and Patient Health Questionnaire-9 were significantly greater in the intervention group compared with placebo with differences of -0.923 (95% CI [-1.62, -0.23]; p = .009) and -1.013 (95% CI [-2.00, -0.02]; p = .045), respectively, but no statistically significant differences were detected between the groups at Week 8. At Week 4, B. longum 1714 significantly improved subscores for Short Form Health Survey-36 (vitality, p = .038; mental health, p = .032; social role functioning, p = .033) compared with placebo, with vitality remaining significant at Week 8 (p = .042). Findings suggest that B. longum 1714 is safe and may exert fast-acting positive effects on various aspects of mood and mental wellness. (PsycInfo Database Record (c) 2026 APA, all rights reserved).