Table 4.
Summary of findings and overall level of evidence as assessed with GRADE.
| All studies | Studies included in the meta-analysis | GRADE domains | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Domain | Method | Total number of participants (no. studies) | Total number of participants (no. studies) | Estimated effect size (p value) | Phase | Study limitations | Inconsistency | Indirectness | Imprecision | Publication bias | Level of evidence |
| Neurochemical | BDNF level in serum, TrkB signaling in lymphocytes | 61 (4) | 36 (3) | 0.91–1.84 (>0.05) | +++ | − | 0∗ | 0 | − | 0∗∗ | + Very low |
| Brain function | fMRI, EEG, TMS, PET | 132 (8) | NA | NA | |||||||
| Brain structure | MRI | 20 (1) | NA | NA | |||||||
GRADE—Grading of Recommendations Assessment, Development and Evaluation. ∗Heterogenous outcomes. ∗∗None of the included studies were registered in Clinical Trials.