Decreased levels of brain-derived neurotrophic factor in the remitted state of unipolar depressive disorder

Hasselbalch BJ, Knorr U, Bennike B, Hasselbalch SG, Greisen Søndergaard MH, Vedel Kessing L. Decreased levels of brain‐derived neurotrophic factor in the remitted state of unipolar depressive disorder. Objective: Decreased levels of peripheral brain‐derived neurotrophic factor (BDNF) have been associated with depression. It is uncertain whether abnormally low levels of BDNF in blood are present beyond the depressive state and whether levels of BDNF are associated with the course of clinical illness. Method: Whole‐blood BDNF levels were measured in blood samples from patients with unipolar disorder in a sustained state of clinical remission and in a healthy control group. Participants were recruited via Danish registers, a method that benefits from the opportunity to obtain well‐matched community‐based samples as well as providing a high diagnostic validity of the patient sample. Results: A total of 85 patients and 50 controls were included in the study. In multiple linear regression analyses, including the covariates age, gender, 17‐item Hamilton Depression Rating Scale scores, body‐mass index, education, smoking and physical exercise, patients with unipolar depressive disorder had decreased levels of BDNF compared to healthy control individuals [B = ?7.4, 95% CI (?11.2, ?3.7), = 0.21 P < 0.001]. No association between course of clinical illness and BDNF levels was present. Conclusion: Whole‐blood BDNF levels seem to be decreased in patients remitted from unipolar depressive disorder, suggesting that neurotrophic changes may exist beyond the depressive state.