Null Effect of Olfactory Training With Patients Suffering From Depressive Disorders-An Exploratory Randomized Controlled Clinical Trial.

Due to a close functional relation between brain areas processing emotion and those processing olfaction, major depression is often accompanied by reduced olfactory function. Such hyposmia can be improved by regular olfactory training (OT) over several months. As this training furthermore improves subjective well-being, we explored whether OT is a useful complementary strategy for depression treatment. A total of 102 depressive outpatients were randomly assigned to OT or a control training condition, which were performed twice a day for 16 weeks. Compliance was continuously monitored. Before and after training we measured depression severity and olfactory function. About half of the patients of both groups did not complete the training. Among the remaining patients, depression severity decreased significantly in both groups. The absence of an interaction effect indicated no selective impact of OT and the variance of depression improvement explained by OT was as little as 0.1%. The low compliance suggests that OT is not feasible for large parts of our sample of depressive outpatients, most likely due to a disease-immanent lack of motivation. In those patients who completed the training, lack of specific effects suggest that OT is not more useful then unspecific activation or attention training. CLINICAL TRIAL REGISTRATION: This clinical trial was registered at German Registry for Clinical Trials (DRKS), main ID: DRKS00016350, URL: http://www.drks.de/DRKS00016350.

The impact of severity, course and duration of depression on olfactory function.

BACKGROUND: People with diagnosed depression often express a reduced olfactory capacity, although previous studies exhibited mixed results. However, research focused mainly on psychiatric inpatients and potential influence variables were rarely considered. We therefore examined the influence of severity, course and duration of depression on olfactory function. METHODS: 101 out-patients with depressive disorders (mean age = 37.8y, SD = 12.6y; 64 women) underwent a detailed medical anamnesis, tests of olfactory threshold and identification and tests of cognitive function. The participants were grouped according to their severity, course and duration of depression. RESULTS: While severity of depressive symptoms did not affect olfactory function, course and duration of depression did. Recurrent depressive disorders were associated with reduced odor identification, and the duration of disease was negatively related to odor threshold. Those results were partly explained by reported frequent colds, which were more prevalent among long lasting depressive patients, and by poor verbal fluency, which was more frequent among recurrent depression. LIMITATIONS: The interpretation is limited by the cross-sectional research design that does not allow causal interpretation, and by the assessment of medical history which was based on patients´ reports. CONCLUSIONS: Our results support the idea that depression is not uniformly related to olfactory impairment, but depends on duration and course of depression. The results generate the hypothesis that reduced olfactory identification is caused by cognitive impairment in recurrent depression. Moreover, the relation between olfactory threshold and depression might be partially caused by a cumulative damage of the olfactory epithelium after frequent respiratory diseases.