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The oxytocin system may be different in autistic people, which could explain some of the deficits in social behavior and cognition associated with autism spectrum disorder. However, studies comparing oxytocin levels in autistic and neurotypical individuals have shown conflicting results and a 2016 meta-analysis on seven studies concluded that there was no significant difference. Here, we greatly expanded the sample of studies to 31, warranting a reassessment of this finding. We searched Web of Science with MEDLINE ® , SciELO Citation Index, and BIOSIS Citation Index for articles that measured oxytocin in plasma/serum ( k = 26 studies), saliva (4), or cerebrospinal fluid (1) in autistic individuals (total n = 1233 participants) compared to neurotypical individuals ( n = 1304). We found that oxytocin levels were significantly lower in autistic people (Cohen’s d = −0.36, 95% confidence interval = −0.61, −0.10, p = 0.007), with no evidence for publication bias. This overall effect was driven entirely by differences among children ( k = 25, d = −0.44, 95% confidence interval = −0.72, −0.16, p = 0.002) but not adults ( k = 6, d = 0.03, 95% confidence interval = −0.55, 0.61, p = 0.92). These results support further research into the use of oxytocin to treat social deficits in children. Lay abstract Oxytocin is a hormone that mediates interpersonal relationships through enhancing social recognition, social memory, and reducing stress. It is released centrally into the cerebrospinal fluid, as well as peripherally into the blood, where it can easily be measured. Some studies indicate that the oxytocin system with its social implications might be different in people with autism spectrum disorder. With summarizing evidence of 31 studies, this meta-analysis suggests that children with autism spectrum disorder have lower blood oxytocin levels compared to neurotypical individuals. This might not be the case for adults with autism spectrum disorder, where we could not find a difference. Our findings motivate further exploration of the oxytocin system in children with autism spectrum disorder. This could lead to therapeutic options in treating autism spectrum disorder in childhood.
John et al. (Sun,) studied this question.