This systematic review and meta-analysis investigated the molecular mechanisms underlying the effects of probiotics on depression. Twenty randomized controlled trials were included, revealing a significant increase in BDNF levels with probiotic treatment compared to placebo (SMD = 0.37, p = 0.02). CRP levels were significantly lower (SMD = −0.47, p = 0.001), and nitric oxide levels significantly higher (SMD = 0.97, p < 0.0001) in probiotic-treated patients with somatic comorbidities. No significant differences were found for other inflammatory markers (IL-1β, IL-6, IL-10, TNF-α, and cortisol). The review concludes that probiotics may be a promising add-on treatment for depression, particularly in those with co-morbid somatic illnesses, but larger, higher-quality trials are needed.

Albert Pinhasov, Michalina Sikorska, Anna Z Antosik-Wójcińska, Monika Dominiak