A systematic review and meta-analysis on the levels of brain-derived neurotrophic factor in insomnia patients with and without comorbid depression

Brain-derived neurotrophic factor (BDNF) plays a crucial role in brain function and sleep regulation. This systematic review and meta-analysis aimed at evidence exclusively from case-control studies examining the BDNF levels among patients with insomnia and people without insomnia. Five e-databases were searched for relevant case-control studies until October 2022. From 1034 records, 7 case-control studies were considered eligible. Four studies found that insomnia significantly decreased BDNF levels. However, two studies found no statistically significant difference between people with insomnia and control, and one study shows an increase in BDNF levels of people with insomnia. Pooled analysis demonstrated the lower levels of BDNF in the patients with insomnia compared to the controls (SMD (95% CI): -2.32 (-3.61, -1.02), p < 0.0001). In general, chronic insomnia leads to decrease in the BDNF levels, especially in patients without depression. Accordingly, these results showed a valuable evidence for decreased BDNF in insomnia patients.