A Poor Sense of Smell Is Linked with Depression in Seniors

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“Take the time to stop and smell the roses.” It’s our metaphor for enjoying life and living in the moment.

But what if you lose your ability to smell the roses? New research from the Johns Hopkins School of Medicine says you’ll be more likely to experience depression.

The findings come out of the university’s Health, Aging, and Body Composition study, an interdisciplinary longitudinal study that investigated risk factors for the decline of function in older adults.

In 1997-98, researchers recruited over 3,000 Americans aged 70-79 and followed them for 16 years, scheduling regular check-ups and tracking major health events. The study focused on healthier seniors and only enrolled participants who, at the beginning of the study, had no trouble walking a quarter mile, climbing 10 steps, or performing normal daily activities. Study data were then used to examine correlations between factors like body composition, strength, metabolic rate, nerve function, cognitive function, mobility, and longevity.

In the third year of the study, 2,125 participants (51 percent female, 37 percent Black) completed an odor identification test. 48 percent of them registered a normal sense of smell, 28 percent showed a decreased sense of smell (a condition called hyposmia), and 24 percent registered a profound loss of their olfactory sense (a condition called anosmia).

Over time, 25 percent of the study’s participants developed what the researchers labeled “significant depressive symptoms.” They divided the depression patterns into three groups: stable low, stable moderate, and stable high. Participants who had demonstrated a poor sense of smell early in the study were 6 percent more likely to experience moderate or high depressive symptoms later in life. This correlation persisted even when the data were controlled for age, income, lifestyle, health factors, and use of antidepressant medication.

“Losing your sense of smell influences many aspects of our health and behavior, such as sensing spoiled food or noxious gas, and eating enjoyment,” says lead study author Vidya Kamath, Ph.D., associate professor of psychiatry and behavioral sciences at Johns Hopkins. “Now we can see that it may also be an important vulnerability indicator of something in your health gone awry. Smell is an important way to engage with the world around us, and this study shows it may be a warning sign for late-life depression.”

Other studies have shown that a poor sense of smell can be an early warning sign of cognitive decline and a symptom of neurodegenerative diseases like Alzheimer’s and Parkinson’s. Adults with better odor identification scores tend to lose brain mass more slowly as they age, especially in the frontal and temporal lobes, which are critical to thinking and memory. Their attention, processing speed, and sensorimotor integration skills also stay sharp longer.

Although this study shows a correlation between having a poor sense of smell and developing depression, it doesn’t prove that one causes the other. Instead, the two may be linked through biological mechanisms, like altered serotonin levels or shrinking brain volume, or behavioral changes, like reduced social interaction and loss of appetite.

What smell can do, though, is serve as an early indicator of a senior’s depression risk and their overall health and well-being. In the future, the team at Johns Hopkins plans to look into whether there are physical changes in the olfactory bulbs of patients diagnosed with depression and to determine whether smell can play a role in intervention strategies to reduce the incidence of late-life depression.