Researchers have unveiled significant new evidence pointing to a connection between a diminished sense of smell and an increased risk of developing late-life depression. Although the findings do not establish a causal relationship between the two, they suggest that the loss of smell may serve as a powerful indicator of overall health and well-being.
According to Vidya Kamath, an associate professor of psychiatry and behavioral sciences at the Johns Hopkins University School of Medicine, a compromised sense of smell has long been recognized as an early warning sign of neurodegenerative disorders like Alzheimer’s and Parkinson’s diseases, as well as a mortality risk. Now, this study underscores its association with depressive symptoms.
The research, conducted using data from the Health, Aging, and Body Composition Study (Health ABC), involved 2,125 participants aged 70 to 73 at the beginning of the eight-year study in 1997-98. At the start, these individuals exhibited no difficulties in physical activities such as walking, climbing stairs, or performing daily tasks. The participants were assessed annually in person and every six months via phone, undergoing tests for odor detection, depression, and mobility.
The study published in the Journal of Gerontology: Medical Sciences, revealed that, in 1999 when the sense of smell was first measured, 48% of participants had a normal sense of smell, 28% exhibited a decreased sense of smell (known as hyposmia), and 24% experienced a profound loss of smell (known as anosmia). Notably, those with a better sense of smell tended to be younger compared to those reporting significant loss or hyposmia.
Over the follow-up period, 25% of participants developed significant depressive symptoms. Further analysis showed that individuals with a decreased or profound loss of smell had a higher risk of developing significant depressive symptoms compared to those with normal olfaction. Additionally, the study identified three depressive symptom “trajectories” within the group: stable low, stable moderate, and stable high depressive symptoms. A poorer sense of smell was associated with an increased likelihood of falling into the moderate or high depressive symptoms groups, indicating a correlation between the severity of smell impairment and the presence of depressive symptoms. These findings remained consistent even after adjusting for various factors such as age, income, lifestyle, health conditions, and antidepressant medication usage.
Vidya Kamath emphasized that losing the sense of smell affects various aspects of health and behavior, such as detecting spoiled food or hazardous gases and enjoying meals. Now, this study suggests that it may also serve as an essential indicator of underlying health issues. Kamath added that smell plays a crucial role in engaging with the world around us, and this research highlights its potential as a warning sign for late-life depression.
The human sense of smell is one of the two chemical senses and relies on specialized sensory cells called olfactory neurons located in the nose. These neurons possess odor receptors that detect molecules released by surrounding substances. The detected molecules are then transmitted to the brain for interpretation. The concentration and combination of these molecules determine the strength and quality of the smell experienced.
The processing of smells occurs in the brain’s olfactory bulb, which is believed to have close interactions with the amygdala, hippocampus, and other brain structures responsible for memory, decision-making, and emotional responses.