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

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.

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.

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.

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.

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.