Association between Obesity and Circulating Brain-Derived Neurotrophic Factor (BDNF) Levels: Systematic Review of Literature and Meta-Analysis

Abstract

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, we performed a meta-analysis carrying out a systematic search in electronic databases. Ten studies (307 obese patients and 236 controls) were included in the analysis. Our 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.

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“…This comes in concordance with a similar meta-analysis performed by Sandrini L and colab. in 2018 [16]. We did not find any correlation between serum levels of BDNF and the periodicity of balneal treatment, either.…”

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“…Thus, it has been difficult to assess circulating BDNF serum levels because BDNF released from platelets during sampling confounds quantitative analyses [14][15][16] . Yet, hundreds of studies have investigated serum BDNF levels in humans to test whether changes can be linked to specific pathologies including for example depression 38 , cardiovascular disease 39 , bipolar disorders 40 , obesity 41 , and neurodegenerative disorders 42 .…”

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“…The parallels extend, however, further. Mutations in the BDNF gene have been found to be associated with hyperphagia and obesity in people (74,75), while exogenous BDNF administration was shown to induce weight loss in animal models (76), although studies on serum BDNF levels in obese individuals have yielded ambiguous results (77). Likewise, metabolomic studies have shown elevated levels of kynurenate associated with high BMI in both adults (78) and children (79).…”