Summary: Loss of smell was linked to a higher risk of developing depression in later life, according to researchers.
Although the study, which lasted for eight years and included more than 2,000 elderly people, did not prove causality, it does suggest that a poor sense of smell may be a sign of overall health and wellbeing. In addition, the findings highlight the complex factors that could influence this relationship, such as inflammation and poor cognition.
This information may pave the way for new approaches to intervention that could lower the likelihood of depression in later life.
When compared to those who had a normal sense of smell, the participants in the study who had a diminished or significant loss of smell had a higher risk of developing significant depressive symptoms over time.
Three “trajectories” of depressive symptoms were found by researchers: a decreased sense of smell is linked to a greater likelihood of falling into the moderate or high depressive symptom groups, with stable low, stable moderate, and stable high depressive symptoms.
According to the findings, biological (such as altered serotonin levels and changes in brain volume) and behavioral (such as decreased social function and appetite) mechanisms may link olfaction and depression.
Source: Johns Hopkins Medicine: Researchers at Johns Hopkins Medicine say they have significant new evidence of a link between the risk of developing late-life depression and a decreased sense of smell in a study that followed over 2,000 older adults who lived in the community for eight years.
Their findings, which appeared in the Journal of Gerontology on June 26, The medical literature suggests that loss of smell may be a powerful indicator of overall health and well-being, but does not demonstrate that it causes depression.
We’ve seen time and time again that a poor sense of smell can be a mortality risk and an early sign of neurodegenerative diseases like Alzheimer’s and Parkinson’s.
Vidya Kamath, Ph.D., associate professor of psychiatry and behavioral sciences at the Johns Hopkins University School of Medicine, states, “This study underscores its association with depressive symptoms.”
“In addition, this study investigates factors such as poor cognition and inflammation that may influence the relationship between olfaction and depression.”
The Health, Aging, and Body Composition Study (Health ABC) was a federal government study that included 2,125 participants. At the beginning of the eight-year study, in 1997–1998, this cohort consisted of healthy older adults between the ages of 70 and 73.
At the beginning of the study, participants demonstrated no difficulties in walking 0.25 miles, climbing 10 steps, or performing normal activities. They were assessed in person every year and by phone every six months. Assessments of depression, mobility, and the ability to detect particular odors were among the tests.
When smell was first measured in 1999, 48% of participants had a normal sense of smell, 28% had a decreased sense of smell, which is called hyposmia, and 24% had a significant loss of the sense, which is called anosmia.
The participants who reported significant loss or hyposmia were generally older than those who had a better sense of smell. 25% of participants experienced significant depressive symptoms during follow-up.
In their subsequent analysis, the researchers discovered that people in the group with normal olfaction had a lower risk of developing significant depressive symptoms at long-term follow-up. Those who reported significant loss or hyposomia tended to be younger than those who had a better sense of smell.
Additionally, the study group’s three depressive symptom “trajectories” were identified by the researchers: symptoms of depression that are stable at low, moderate, and high levels.
A participant’s likelihood of falling into the moderate or high depressive symptoms group was correlated with their sense of smell, meaning that the worse a person’s sense of smell, the worse their depression symptoms.
After adjusting for age, income, lifestyle, health factors, and antidepressant use, these results persisted.
“The loss of our sense of smell has an impact on many aspects of our health and behavior, including our ability to detect spoiled food or noxious gas and our enjoyment of eating. According to Kamath, “now we can see that it may also be an important vulnerability indicator of something going wrong in your health.”
“This study shows that smell may be a warning sign for late-life depression,” the researchers write. “Smell is an important way to engage with the world around us.”
Smell is one of two chemical senses that humans have. It works by using specialized sensory cells in the nose called olfactory neurons.
These neurons have one scent receptor; It detects molecules released by things around us and sends them to the brain for analysis.
The stronger the smell, the higher the concentration of these smell molecules, and different combinations of molecules cause different sensations.
The olfactory bulb of the brain is thought to interact closely with the amygdala, hippocampus, and other brain structures that control and facilitate memory, decision-making, and emotional responses in order to process smell.
According to the findings of their study, the researchers at Johns Hopkins believe that there may be a connection between olfaction and depression through both behavioral and biological mechanisms, such as decreased social function and appetite and altered serotonin levels in the brain.
The researchers intend to replicate their findings from this study in additional groups of older adults and examine changes in people’s olfactory bulbs to ascertain whether this system is altered in depression patients. They also intend to investigate whether smell can be incorporated into intervention strategies to reduce the likelihood of depression in later life.
Kening Jiang, Danielle Powell, Frank Lin, and Jennifer Deal, all of the Johns Hopkins University School of Medicine and Bloomberg School of Public Health, contributed to this study as well. The University of Connecticut’s Kevin Manning; Willa Brenowitz, Kristine Yaffe, and R. Scott Mackin from the University of California, San Francisco; Eleanor Simonsick and Keenan Walker from the National Institute on Aging; and Michigan State University’s Honglei Chen.
According to the policies of the Johns Hopkins University School of Medicine, no authors disclosed any conflicts of interest related to this research.
Funding: The Intramural Research Program of the National Institutes of Health, the National Institute on Aging, and the National Institute of Nursing Research all provided funding for this work: National Aging Research Center.
Background Olfactory Dysfunction and Depression Trajectories in Community-Dwelling Older Adults We investigated the connection between well-functioning older adults’ baseline olfactory performance, incidentally significant depressive symptoms, and longitudinal depression trajectories. As potential mediators, inflammation and cognitive status were investigated.
Methods In the Health, Aging, and Body Composition study, older adults (n = 2 125, 71–82 years old, 51% female, 37% Black) completed an odor identification task in Year 3 (our study baseline). Over the course of eight years, multiple visits were used to gather information on cognitive assessments, depressive symptoms, and inflammatory markers. The relationship between baseline olfaction, incident depression, and longitudinal depression trajectories was examined using discrete-time complementary log-log models, group-based trajectory models, and multivariable-adjusted multinomial logistic regression. The impact of cognitive status on these relationships was looked at using mediation analysis.
Results: At follow-up, people with lower olfaction were more likely to experience significant depressive symptoms (hazard ratio = 1.04, 95% CI: 1.00, 1.08). Poorer olfaction was associated with a 6% higher risk of membership in the stable moderate pattern of the three identified patterns of longitudinal depression scores (stable low, stable moderate, and stable high) (relative risk ratio [RRR] = 1.06, 95% CI: 1.02, 1.10)/highly stable (RRR = 1.06, 95 percent CI: 1.00, 1.12), in contrast to the stable low group. Olfactory performance and incident depression symptom severity were partially mediated by poor cognitive status, but not inflammation.
Conclusions Poor olfaction may be a warning sign that a person is more likely to develop depression in later life. These results emphasize the significance of gaining a deeper comprehension of olfaction in late-life depression as well as the demographic, cognitive, and biological factors that have an impact on these relationships over time.