Effect of smoking on Brain-Derived Neurotrophic Factor (BDNF) blood levels: A systematic review and meta-analysis

Background: Brain-Derived Neurotrophic Factor (BDNF) is a neurotrophin that plays a crucial role in neuronal survival and plasticity. Previous studies have suggested that smoking may influence BDNF levels, but the findings have been inconsistent. Methods: A comprehensive search of electronic databases was conducted to identify relevant studies. Inclusion criteria were applied to select studies that investigated the relationship between smoking and blood levels of BDNF. A random-effects model was used to estimate the overall effect size. Results: A total of 23 studies were included. The meta-analysis revealed a significant association between smoking and increased blood levels of BDNF (standardized mean difference [SMD] = −0.38, 95 % confidence interval [CI] 0.15 to 0.62, p = 0.002). Subgroup analyses based on BDNF source showed a significant increase in plasma-derived BDNF levels (SMD = 1.02, 95 % CI 0.50 to 1.53, p = 0.0001), while no significant difference was observed in serum-derived BDNF levels (SMD = 0.02, 95 % CI -0.19 to 0.22, p = 0.87). The pooled analysis revealed a non-significant difference in blood levels of BDNF between former smokers and non-smokers (random-effects model, SMD = 0.21, 95 % CI -0.04 to 0.46, p = 0.1). Conclusion: Smokers exhibited significantly higher plasma levels of BDNF compared to non-smokers. Further research is needed to elucidate the underlying mechanisms and explore the potential therapeutic implications of targeting BDNF in smoking.