Impact of probiotic supplementation on serum levels of brain-derived neurotrophic factor: GRADE-based dose-response meta-analysis
Reza Hashemi, Mohammad M. Hussein M. Raouf, Tanya S. Salih, Marzieh Feyzpour, Maryam Eskandarioun, Najmeh Nezamabadipour, Hossein Gandomkar
Abstract
BACKGROUND: Brain-derived neurotrophic factor (BDNF) is a key neurotrophin involved in neuroplasticity and cognitive function, with its dysregulation linked to neurodegenerative and psychiatric disorders. Probiotics, through the gut-brain axis, may modulate BDNF levels, but evidence remains inconsistent. This meta-analysis aimed to evaluate the effect of probiotic supplementation on serum BDNF levels and explore dose-response relationships. METHODS: We conducted a systematic review and meta-analysis, searching PubMed, Scopus, Cochrane Central, Web of Science, and Embase up to April 2025, following PRISMA guidelines (PROSPERO: CRD420251036851). Randomized controlled trials (RCTs) involving adults (≥ 18 years) with a minimum 2-week probiotic intervention and reported BDNF levels were included. A random-effects model calculated weighted mean differences (WMDs), and fractional polynomial modeling assessed non-linear dose-response relationships. Heterogeneity, publication bias, and evidence quality (GRADE) were evaluated. RESULTS: From 20 RCTs (n = 2372 participants), probiotic supplementation significantly increased serum BDNF levels (WMD = 0.18, 95% CI: 0.11–0.26; P < 0.001), with high heterogeneity (I²=96%, P < 0.001). Subgroup analysis identified longer follow-up duration (> 10 weeks) as a heterogeneity source (WMD = 1.69, 95% CI: 1.13–2.26; I²=46%). A significant non-linear association was found between treatment duration and BDNF levels (Pnonlinearity = 0.02), but not dosage (Pnonlinearity = 0.277). No significant publication bias was detected (Begg’s P = 0.15; Egger’s P = 0.29). Evidence quality was very low per GRADE. CONCLUSIONS: Probiotic supplementation increases serum BDNF levels, particularly with prolonged interventions (> 10 weeks), suggesting its potential as an adjunctive therapy for BDNF-related disorders, warranting further high-quality research. CLINICAL TRIAL NUMBER: Not applicable.