Bad sense of smell may be linked to depression in older people: study

Their findings, published in the Journal of Gerontology: Medical Sciences, do not prove that loss of smell causes depression, but suggest that it may serve as a powerful indicator of overall health and well-being.

“We’ve seen repeatedly that bad smell can be an early warning sign of neurodegenerative diseases like Alzheimer’s and Parkinson’s, as well as mortality risk. This study highlights its connection to depressive symptoms,” says Vidya Kamata, Ph.D., associate professor of psychiatry and behavioral sciences at the Johns Hopkins University School of Medicine. “Furthermore, this study examines factors that may influence the link between olfaction and depression, including poor cognition and inflammation.”

The study used data from 2,125 participants in a federal government study known as the Health, Aging, and Body Composition (Health ABC) study. This cohort consisted of a group of healthy older adults aged 70 to 73 years at the start of the eight-year study in 1997–1998. At the start of the study, participants had no difficulty walking 0.25 miles, climbing 10 steps, or performing normal activities, and were assessed in person annually and by phone every six months. Tests included ability to detect certain odors, depression and mobility ratings.

In 1999, when olfaction was first measured, 48% of participants had a normal sense of smell, 28% had a reduced sense of smell, known as hyposmia, and 24% had a profound sensory loss, known as anosmia. Participants with better olfaction tended to be younger than those who reported significant loss or hyposmia. During follow-up, 25% of participants developed significant depressive symptoms. In further analysis, the researchers found that individuals with reduced or significant olfactory loss were at greater risk of developing major depressive symptoms during longitudinal follow-up than those in the normal olfactory group. Participants with a better sense of smell tended to be younger than those who reported significant loss or hyposomia.

The researchers also identified three “trajectories” of depressive symptoms 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 group, meaning that the worse a person’s sense of smell, the higher the depressive symptoms. These findings persisted after adjustment for age, income, lifestyle, health factors, and antidepressant use.

“Loss of our sense of smell affects many aspects of our health and behaviour, such as the sensation and enjoyment of eating spoiled food or noxious gases. We now see that it can also be an important indicator of vulnerability that something has gone wrong in your health,” says Kamath. “Smell is an important way of interacting with the world around us, and this study shows that it can be a warning sign of late-onset depression.”

The human sense of smell is one of the two chemical senses. It works through specialized sensory cells called olfactory neurons located in the nose. These neurons have a single odorant receptor; it picks up molecules released by the substances around us, which are then passed on to the brain for interpretation. The higher the concentration of these scent molecules, the stronger the smell, and different combinations of molecules create different sensations.

Smell is processed in the brain’s olfactory bulb, which is thought to interact closely with the amygdala, hippocampus, and other brain structures that regulate and mediate memory, decision-making, and emotional responses.

Johns Hopkins researchers say their study suggests that olfaction and depression may be linked to both biological (eg, altered serotonin levels, changes in brain volume) and behavioral (eg, reduced social function and appetite) mechanisms.

The researchers plan to replicate their findings from this study in a larger group of older adults and examine changes in individuals’ olfactory bulbs to determine if this system is indeed altered in those diagnosed with depression. They also plan to test whether scent can be used in intervention strategies to reduce the risk of late-life depression.

Other scientists who participated in the study include Kenning Jiang, Daniela Powell, Frank Lin, and Jennifer Diehl from the Johns Hopkins University School of Medicine and the Bloomberg School of Public Health; Kevin Manning of the University of Connecticut; R. Scott Mackin, Willa Brenowitz, and Kristine Yaffe of the University of California, San Francisco; Keenan Walker and Eleanor Simonsick of the National Institute on Aging; and Honglei Chen of Michigan State University.

In accordance with Johns Hopkins University School of Medicine policy, no authors have declared any conflicts of interest related to this study.

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. (ANI)

This report is automatically generated from the ANI news service. ThePrint takes no responsibility for its content.

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