Decreased sense of smell in adults linked to depression later in life

Researchers at Johns Hopkins Medicine claim to have found significant new evidence of a connection between the diminished sense of smell and the risk of developing late-life depression. While their findings do not demonstrate that loss of smell causes depression, it suggests that it may serve as a potent indicator of overall health and well-being. The results are published in the Journal of Gerontology: Medical Sciences.
“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,” Vidya Kamath, Ph.D., associate professor of psychiatry and behavioural sciences at the Johns Hopkins University School of Medicine.
They added, “This study explores factors that might influence the relationship between olfaction and depression, including poor cognition and inflammation.”
The study used data gathered from 2,125 participants in a federal government study, the Health, Aging and Body Composition Study (Health ABC). This cohort comprised 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 detecting certain odours, depression" depression and mobility assessments.
Kamath said, “Losing your sense of smell influences many aspects of our health and behaviour, 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. 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.”
The 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 researchers say their study suggests that olfaction and depression" depression may be linked through both biological (e.g., altered serotonin levels, brain volume changes) and behavioural (e.g., reduced social function and appetite) mechanisms.