Fig. 3

(a) Direct comparison of the effect sizes of the different studies in mania, depression, and euthymia. Peripheral brain-derived neurotrophic factor (BDNF) levels were equally decreased in mania and depression (P = 0.340), and both manic and depressive states presented BDNF levels decreased when compared to euthymic state (P = 0.002). (b) Meta-regression of the effect sizes of peripheral BDNF levels against severity of mania as assessed by the Young Mania Rating Scale (YMRS) scores, showing more accentuated decreases in BDNF levels with increase in YMRS scores (P = 0.004). (c) Meta-regression of the effect sizes of peripheral BDNF levels against severity of depression as assessed by the Hamilton Depression Rating Scale (HDRS) scores, showing more accentuated decreases in BDNF levels with increase in HDRS scores (P = 0.018). (d) Meta-regression of the effect sizes of peripheral BDNF levels against duration of illness in years in euthymic subjects, showing no association between BDNF levels and duration of bipolar illness in years during euthymia (P = 0.577)