In a study that followed more than 2,000 community-dwelling older adults over eight years, researchers say they have significant new evidence of a link between decreased sense of smell and risk of developing late-life depression.
“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,” says Vidya Kamath, Ph.D. “Additionally, this study explores factors that might influence the relationship between olfaction and depression, including poor cognition and inflammation.”
The study was composed of a group of healthy older adults ages 70-73 at the start of the eight-year study period in 1997-98. Participants showed no difficulties in walking 0.25 miles, climbing 10 steps or performing normal activities at the start of the study, and were assessed in person annually and by phone every six months. Tests included those for the ability to detect certain odors, depression and mobility assessments.
When smell was first measured, 48% of participants displayed a normal sense of smell, 28% showed a decreased sense of smell, known as hyposmia, and 24% had a profound loss of the sense, known as anosmia. Participants with a better sense of smell tended to be younger than those reporting significant loss or hyposmia. Over follow-up, 25% of participants developed significant depressive symptoms. When analyzed further, researchers found that individuals with decreased or significant loss of smell had increased risk of developing significant depressive symptoms at longitudinal follow-up than those in the normal olfaction group. Participants with a better sense of smell tended to be younger than those reporting significant loss or hyposmia.
Researchers also identified three depressive symptom “trajectories” in the study group: meaning that the worse a person’s sense of smell, the higher their depressive symptoms. These findings persisted after adjusting for age, income, lifestyle, health factors and use of antidepressant medication.
“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.”says Kamath.
Smell is 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 olfaction and depression may be linked through both biological and behavioral mechanisms.
The researchers plan to replicate their findings from this study in more groups of older adults, and examine changes to individuals’ olfactory bulbs to determine if this system is in fact altered in those diagnosed with depression.
Vidyulata Kamath, Kening Jiang, Kevin J Manning, R Scott Mackin, Keenan A Walker, Danielle Powell, Frank R Lin, Honglei Chen, Willa D Brenowitz, Kristine Yaffe, Eleanor M Simonsick, Jennifer A Deal. Olfactory Dysfunction and Depression Trajectories in Community-Dwelling Older Adults. The Journals of Gerontology: Series A, 2023; DOI: 10.1093/gerona/glad139
Johns Hopkins Medicine. “Poor sense of smell linked to increased risk of depression in older adults.” ScienceDaily. ScienceDaily, 26 June 2023. <www.sciencedaily.com/releases/2023/06/230626164246.htm>.
Photo by Ruslan Zh