New research published in the journal Scientific Reports highlights the intricate relationship between depression and sense of smell. The study found that participants’ symptoms of depression dropped as their odor identification improved, particularly among those with an impaired sense of smell.
A wealth of research has pointed to a relationship between depression and olfactory function. For example, older adults who have lost their sense of smell are more likely to develop depressive symptoms in the future. Interestingly, this relationship seems to be reciprocal, with patients with depression demonstrating an impaired sense of smell.
Studies have also suggested that enhancing smell through olfactory training can improve mood, but it is unclear whether these benefits stem from the increased exposure to smells during training, or from the improvement in olfaction on its own.
“Considering that depression is among the most common psychiatric diseases, a multifaceted approach to its treatment would be beneficial,” said lead researcher Agnieszka Sabiniewicz, a member of the Smell and Taste Clinic at Dresden University of Technology. “At the same time, people suffering from olfactory dysfunction often report mood deterioration, and numerous research shown a connection between olfaction and depression. However, the nature of this connection still remains to be explored.”
Sabiniewicz and her research team devised a study to explore whether an improvement in olfactory function would coincide with an improvement in depressive symptoms, absent of olfactory training. The study was focused primarily on patients with dysosmia, an impairment in olfactory function.
The sample consisted of 171 participants between the ages of 14 and 87 who had visited a smell and taste clinic due to an olfactory impairment. According to olfactory testing, the majority of the participants (157) met the threshold for dysosmia, while a small minority (14) were deemed to have a normal sense of smell.
On two occasions, roughly 11 months apart, each participant’s sense of smell was tested and their depression symptoms were assessed. Olfactory function was assessed with tests of odor threshold, odor discrimination, and odor identification, where the three test scores were summed as a measure of general olfactory function. Depression symptom severity was assessed with the General Depression Scale—long form.
The researchers then analyzed whether changes in participants’ olfactory function coincided with changes in their depression symptom severity. The results revealed that improvements in depression severity were tied to improvements in odor identification and general olfactory function, especially among patients with dysosmia. Notably, participants with dysosmia showed improvements in odor identification that were five times stronger compared to the entire sample.
“Many scientific studies demonstrated that there is a link between olfaction and depression,” Sabiniewicz told PsyPost. “This connection resulted in practical attempts to improve mood via olfactory training, that is, frequent exposition to odors. While this approach was successful, our study is first to demonstrate that olfaction may be directly related to mood. In other words, people who improved in olfaction, without olfactory training, showed a decrease in depression severity. This is a fascinating finding that allows extending perspective on the connection between olfaction and depression.”
While there are different theories concerning the link between sense of smell and depression, some research suggests that the relationship is driven by shared connections within the brain. Information pertaining to smell passes through many brain areas that also play a role in affective functions like the processing of emotions. These regions include the amygdala, hippocampus, and anterior cingulate cortex.
Among limitations, the study authors acknowledge that their sample consisted entirely of individuals who had visited a treatment center seeking help for olfactory impairment. As such, the participants may have demonstrated a greater number of depression symptoms compared to people with olfactory issues who do not seek counseling.
“It should be considered that for people searching for clinical counselling, their smell impairment usually causes emotional suffering,” Sabiniewicz explained. “Thus, the present study sample probably showed more depressive symptoms compared to other people with smell impairment who do not feel the need to be cured.”
The study, “Symptoms of depression change with olfactory function”, was authored by Agnieszka Sabiniewicz, Leonie Hoffmann, Antje Haehner, and Thomas Hummel.