The reason for BDNF reductions in this sample receiving TAU over a 3 month period is unclear; for example, even over several years a lack of significant change in serum BDNF has been reported.28,29 Conversely, a report of reduced BDNF manifesting over a long period in people who had a depressive illness compared with those without concluded that the BDNF can be considered a state marker of affective illness.30 However, our population were not experiencing depressive symptoms during the trial and subsyndromal depression severity did not differ between groups or timepoints.5 Here, BDNF is linked to depressive disorder.