Reduction in brain-derived neurotrophic factor (BDNF) expression in the brain as well as mutations in BDNF gene and/or of its receptor are associated to obesity in both human and animal models. However, the association between circulating levels of BDNF and obesity is still not defined. To answer this question, a meta-analysis has been performed to carry out a systematic search in electronic databases.
The data show that obese patients have levels of BDNF similar to those of controls (SMD: 0.01, 95% CI: -0.28, 0.30, p = 0.94). The lack of difference was further confirmed both in studies in which BDNF levels were assessed in serum (MD: -0.93 ng/mL, 95% CI: -3.34, 1.48, p = 0.45) and in plasma (MD: 0.15 ng/mL, 95% CI: -0.09, 0.39, p = 0.23). Data evaluation has shown that some bias might affect BDNF measurements (e.g., subject recruitment, procedures of sampling, handling, and storage), leading to a difficult interpretation of the results. Standardization of the procedures is still needed to reach strong, affordable, and reliable conclusions.