In a recent study conducted by researchers at Johns Hopkins Medicine, the team uncovered significant evidence of a relationship between a decreased sense of smell and a heightened risk of developing late-life depression.

According to the researchers, the study does not prove causation. Nonetheless, they believe that the link may act as a critical overall health indicator.

“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,” said Vidya Kamath of Johns Hopkins University School of Medicine.

“This study underscores its association with depressive symptoms. Additionally, this study explores factors that might influence the relationship between olfaction and depression, including poor cognition and inflammation.”

The research relied on data collected from 2,125 individuals in the Health, Aging, and Body Composition Study (Health ABC), a federal government study. This participant pool was comprised of healthy older adults between the ages of 70 and 73 when the eight-year-long study period began from 1997 to 1998.

The participants did not have any difficulty climbing 10 steps, walking 0.25 miles, or completing typical activities at the onset of the research. Then, they were assessed by phone every six months and in person every year.

These assessments focused on mobility tests, depression, and the ability to detect certain odors.

Sense of smell was first measured in 1999, at which point just under half of the participants– 48%– displayed a normal sense of smell. At the same time, 28% of the participants showed hyposmia, or a decreased sense of smell, and 24% showed anosmia or a significant loss of smell.

The participants who had better olfaction tended to be younger in age than the participants reporting significant smell loss or hyposmia. Throughout follow-up assessments, 25% of the study participants ultimately developed severe depressive symptoms.

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Upon further analysis, the team discovered that at longitudinal follow-up, participants who suffered from either decreased or significant smell loss also had a heightened risk of developing severe depressive symptoms as opposed to participants in the normal olfaction group.

The researchers were also able to identify three different “trajectories” for depressive symptoms: stable low, stable moderate, and stable high depressive symptoms.

It was found that a poorer sense of smell was linked to an increased chance of participants belonging to the moderate or high depressive symptoms groups. So, participants with a worse sense of smell had more severe depressive symptoms.

Interestingly, this link also persisted even after adjusting for various factors, including age, lifestyle, income, health factors, and the use of antidepressants.

“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 explained.

“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.”

Sense of smell is one of humans’ two chemical senses– working via olfactory neurons, or specialized sensory cells, that are located in the nose.

Olfactory neurons have an odor receptor that detects molecules released by substances in our environment and relay these substances back to the brain to be interpreted.

When there is a higher concentration of smell molecules, smells are stronger. And varying combinations of molecules ultimately cause different sensations.

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

So, the researchers believe their findings suggest that olfaction and depression could be linked through both biological and behavioral mechanisms. Biological mechanisms may include brain volume changes and altered serotonin levels; meanwhile, behavioral mechanisms may include appetite changes and reduced social function.

The team now intends to replicate the findings of this study among additional groups of older adults, with the goal of examining changes to individual olfactory bulbs to figure out whether the brain system is altered among people diagnosed with depression.

Finally, the researchers also plan to determine whether smell can be used alongside intervention strategies to mitigate the risk of developing late-life depression.

To read the study’s complete findings, which have since been published in The Journals of Gerontology: Series A, visit the link here.

You can read the original post on Reddit here.

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