The Impact of Probiotics on Core Autism Symptoms - A Systematic Review and Meta-analysis of Randomized Clinical Trials

Background & Aims: Studies have shown evidence of gut dysbiosis in individuals with autism spectrum disorder (ASD). Various microbiome-modifying treatments, including probiotics, have been proposed. This review systematically assessed the evidence on the effects of probiotics on core autism symptoms in children with ASD.

Methods: We performed a comprehensive literature search in Medline, Embase, CENTRAL, PsycInfo, and clinical trial registries, up to March 2023, and updated on January 10, 2024. Randomized controlled trials (RCTs) of parallel-group and cross-over designs were eligible. The population included individuals below 20 years of age diagnosed with ASD. Trials evaluating the effects of probiotics (any strain or dose) compared to placebo, no treatment, or another intervention were included. The outcomes of interest included the core autism symptoms: deficits in social skills, communication skills, and restricted, repetitive behaviors. No language restrictions were applied. Studies were excluded if an additional active compound was administered. The risk of bias was assessed using the Revised Cochrane Risk of Bias tool (RoB 2). This review was registered in PROSPERO (CRD42023393000).

Results: In total, 12 RCTs assessing 630 participants were included. A borderline significant beneficial effect of probiotics on core ASD symptoms was found (8 RCTs, mean difference -0.21; 95% CI -0.39 to -0.03). Subgroup analysis according to study type showed a significant positive effect in parallel group trials (6 RCTs, mean difference -0.26; 95% CI -0.48 to -0.05). The pooled effect estimates for the other outcomes didn't reveal significant differences between the groups. Importantly, the risk of bias was high in nine studies.

Conclusions: Available data do not provide high-quality evidence supporting the use of probiotics for ASD symptoms in children.