Researchers at Johns Hopkins Medicine say they have important new evidence of an association between loss of smell and the risk of developing depression in late life in a study of more than 2,000 older adults who lived in the community for eight years. . Their findings, published in the Journal of Gerontology: Medical Sciences, do not demonstrate that loss of smell causes depression, but suggest that it may serve as a powerful indicator of overall health and well-being.
Vidya Kamath says, “We have seen time and time again that a poor sense of smell can be an early warning sign of neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease, as well as increased risk of death. This study supports its association with depressive symptoms.” underlines the relationship. Associate Professor of Psychiatry and Behavioral Sciences at the Johns Hopkins University School of Medicine, Ph.D.
“Additionally, this study explores factors that may influence the relationship between smell and depression, including poor cognition and inflammation.” The study used data collected from 2,125 participants in a federal government study called the Health, Aging, and Body Composition Study (Health ABC). The cohort was composed of a cohort of healthy older adults aged 70–73 years at the start of the eight-year study period in 1997–98.
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Participants had no difficulty walking 0.25 miles, climbing 10 stairs, or doing normal activities at the start of the study, and were assessed annually in person and every six months by phone. The tests included assessment of the ability to detect certain odors, depression and mobility.
In 1999, when smell was first measured, 48% of participants displayed a normal sense of smell, 28% had a loss of smell, known as hyposmia, and 24% had a profound loss of sense. , which is known as anosmia. Participants with a better sense of smell were younger than those reporting significant impairment or hyposmia. During follow-up, 25% of participants developed significant depressive symptoms.
When further analyzed, the researchers found that individuals with loss or significant loss of smell had an increased risk of developing significant depressive symptoms at longitudinal follow-up compared to those in the normal olfactory group. Participants with a better sense of smell were younger than those reporting significant impairment or hyposmia.
The researchers also identified three depressive symptom “trajectories” in the study group: stable low, stable moderate and stable high depressive symptoms. A poorer sense of smell was associated with an increased likelihood of a participant falling into the moderate or high depressive symptom clusters, meaning that the worse a person’s sense of smell, the higher their depressive symptoms. These findings held even after adjusting for age, income, lifestyle, health factors, and antidepressant medication use.
“Losing the power of smell affects many aspects of our health and behaviour, such as smelling spoiled food or noxious gas and enjoying eating. Now we can see that it may also be an important vulnerability indicator to disturbances in your health. could.” Kamath says. “Smell is an important way to connect with the world around us, and this study shows it may be a warning sign for late-stage depression.”
The human sense of smell is one of the two chemical senses. It works through specialized sensory cells, called olfactory neurons, which are found in the nose. These neurons contain an odorant receptor; It picks up molecules released by substances around us, which are then sent to the brain for interpretation. The higher the concentration of these odor molecules, the stronger the odor, and different combinations of molecules result in different sensations.
Smells are processed in the brain’s olfactory bulb, which is believed to interact closely with the amygdala, hippocampus, and other brain structures that regulate and enable memory, decision-making, and emotional responses. The Johns Hopkins researchers say their study suggests that smell and depression may be linked through both biological (eg, altered serotonin levels, changes in brain volume) and behavioral (eg, reduced social functioning and appetite) mechanisms. Can be connected through.
The researchers plan to replicate their findings from this study in more cohorts of older adults, and examine changes in individuals’ olfactory bulbs to determine whether this system is indeed altered in those with depression. . They also plan to investigate whether smell can be used in intervention strategies to reduce the risk of depression in late life.
Other scientists who contributed to this research are Kening Jiang, Danielle Powell, Frank Lin and Jennifer Deal of the Johns Hopkins University School of Medicine and the Bloomberg School of Public Health; Kevin Manning of the University of Connecticut; University of California, San Francisco’s R. Scott Mackin, Willa Brenowitz and Christine Yaffe; Keenan Walker and Eleanor Simoncic of the National Institute on Aging; and Honglei Chen of Michigan State University.
None of the authors declared a conflict of interest related to this research under Johns Hopkins University School of Medicine policies.
This work was supported by the National Institute on Aging, the National Institute of Nursing Research, and the Intramural Research Program of the National Institutes of Health: National Institute on Aging.