The therapeutic effects of probiotics on core and associated behavioral symptoms of autism spectrum disorders: a systematic review and meta-analysis

Abstract

Background The current study aimed at investigating the efficacies of probiotics in alleviating the core and associated symptoms of autism spectrum disorder (ASD), which was not adequately addressed in the literature. Methods Randomized placebo-controlled trials were identified through searching major electronic databases from inception to Nov 2023. The outcome of interests included improvements in the total and associated symptoms of ASD. Outcomes were quantitatively expressed as effect size (ES) based on standardized mean difference (SMD) with 95% confidence interval (CI). Results Ten studies with 522 participants (mean age: 8.11) were included in this meta-analysis. The primary results revealed a significant improvement in the total symptoms of ASD in individuals receiving probiotics compared with the controls (SMD= -0.19, p = 0.03, ten studies with 522 participants) but not in the core symptoms of ASD including repetitive restricted behaviors and problems with social behaviors or communication. Subgroup analyses demonstrated an association between a significant improvement in the total symptoms of ASD and the use probiotics relative to their controls only in studies that used multiple-strain probiotics (SMD= -0.26, p = 0.03, five studies with 288 participants) but not in those using single-strain probiotics. Our results on secondary outcomes only showed a significantly greater improvement in adaptation (SMD = 0.37, p = 0.03, three studies with 139 participants) and a trend of greater improvement in symptoms of anxiety in the probiotics group than that in the control group (SMD= -0.29, 95% CI: -0.60 to 0.02, p = 0.07, three studies with 163 participants) but failed to show greater improvement in the probiotics group regarding the symptoms of irritability/aggression, hyperactivity/impulsivity, inattention and parental stress. Conclusions Our study supported the use of probiotics for alleviating the overall behavioral symptoms of ASD, mainly in those receiving multiple-strain probiotics as supplements. However, rather than improvement in the core symptoms of ASD, probiotics use was only associated with greater improvement in adaptation and perhaps anxiety. Nevertheless, our results, which were derived from a limited number of available trials, warrant further large-scale clinical investigations for verification.