Meta‐analysis of peripheral insulin‐like growth factor 1 levels in schizophrenia

OBJECTIVE: We aimed to investigate if there is a significant difference in peripheral insulin‐like growth factor 1 (IGF‐1) levels between schizophrenia patients and healthy controls and to determine whether a difference exists before and after initiation of antipsychotics. METHODS: PubMed/MEDLINE, Scopus, and Web of Science were searched up to March 27, 2022. Original clinical studies of any type that reported peripheral blood, serum or plasma IGF‐1 levels measured after fasting in schizophrenia patients and/or healthy control group were selected based on inclusion and exclusion criteria. Data were analyzed using Meta‐Essentials: Workbooks for meta‐analysis and pooled through random‐effects meta‐analyses. RESULTS: Twelve publications met eligibility criteria. Schizophrenia patients under antipsychotic treatment had significantly lower peripheral IGF‐1 levels compared to healthy controls (n = 632, Hedges’ g –0.42, 95% CI from –0.79 to –0.04, p = .006, I(2) = 70.38%), while no significant difference was found between schizophrenia patients regardless of the antipsychotic treatment status and healthy controls, as well as between antipsychotic naïve or free schizophrenia patients and healthy controls, and before and after initiation of antipsychotic treatment. However, high heterogeneity was observed and its potential sources in some of the subgroup analyses included sample type and region. CONCLUSIONS: Schizophrenia patients under antipsychotic treatment seem to have lower peripheral IGF‐1 levels compared to healthy controls. Additional studies with larger and more homogenous samples are needed to confirm these findings.