BDNF and anxiety disorder: In five of these reports (Dell'Osso et al., 2009; Maina et al., 2010; Strohle et al., 2010; dos Santos et al., 2011; Wang et al., 2011), BDNF levels (both serum and plasma) in patients with an anxiety disorder were lower than in participants without an anxiety disorder, with effect sizes ranging from moderate to large.