As Seniors' Sense of Smell Declines, Their Risk for Depression Rises
Researchers have found significant new evidence of a link between a decreased sense of smell and the risk of developing depression later in life.
Known as hyposmia, or at its most profound, anosmia, the condition has been associated previously with Alzheimer's disease in older adults.
“We've seen repeatedly 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 a mortality risk. This study underscores its association with depressive symptoms,” said Vidya Kamath, an associate professor of psychiatry and behavioral sciences at Johns Hopkins University School of Medicine in Baltimore.
“Additionally, this study explores factors that might influence the relationship between olfaction and depression, including poor cognition and inflammation," she said in a university news release.
In the study, researchers followed more than 2,100 community-dwelling older adults over eight years, using data from the Health, Aging and Body Composition Study (Health ABC).
These older adults were healthy and ages 70 to 73 when the study period began in 1997. They each had no difficulty walking a quarter of a mile, climbing 10 steps and performing normal activities.
The participants were assessed in person each year and by phone every six months.
Smell was first measured in 1999, when 48% of participants displayed a normal sense of smell. Another 28% showed a decreased sense of smell and 24% had a profound loss of the sense.
Those whose sense of smell remained stronger tended to be younger than those reporting significant loss of smell.
About 25% of participants developed significant depressive symptoms during the follow-up period.
The authors found that those with decreased or significant loss of smell had an increased risk of developing significant depressive symptoms.
During the study, researchers also identified three depressive symptom trajectories. The participants were stable low, stable moderate and stable high in depressive symptoms.
Having a poorer sense of smell was associated with an increased chance of a participant falling into the moderate or high depressive symptoms groups, which indicated that having a worse sense of smell was associated with higher depressive symptoms.
"Losing your sense of smell influences many aspects of our health and behavior, such as sensing spoiled food or noxious gas, and eating enjoyment. Now we can see that it may also be an important vulnerability indicator of something in your health gone awry,” Kamath said. “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.”
A person's sense of smell works through what are called olfactory neurons, located in the nose.
These have one odor receptor, which picks up molecules released by substances and then relays them to the brain.
That smell is processed in the brain's olfactory bulb, which scientists think interacts closely with the amygdala, hippocampus and other brain structures that regulate and enable memory, decision-making and emotional responses.
Olfaction and depression may be linked through both biological and behavioral routes, such as altered serotonin levels and reduced social function, for example, the authors said.
They plan to continue studying this in more groups of older adults. Among the areas they would like to pursue is whether individuals' olfactory bulbs are altered in people who have depression. The team also plans to investigate whether smell can be used to help treat depression late in life.
The findings, supported by the U.S. National Institutes of Health, were published June 26 in the Journal of Gerontology: Medical Sciences.
The U.S. National Institutes of Health has more on sense of smell.
SOURCE: Johns Hopkins Medicine, news release, June 26, 2023