Connection Between Diminished Sense of Smell and Higher Likelihood of Depression in the Elderly

In an eight-year study following more than 2,000 older adults, scientists at Johns Hopkins Medicine have discovered an association between a reduced ability to smell and an increased risk of late-life depression. Although the findings do not establish a direct cause, they hint that a decreased sense of smell might be a significant marker for general health and well-being issues.

Historically, hyposmia has been connected to Alzheimer’s disease and other dementia types in older individuals, and recent findings reinforce its link to other age-associated ailments.

The research, which tracked over 2,000 elderly people living in various communities for eight years, has unearthed convincing evidence pointing to a connection between a decreased sense of smell and a greater chance of experiencing depression later in life.

The results, recently published in the Journal of Gerontology: Medical Sciences, don’t confirm that a lack of smell directly results in depression. Still, they emphasize its potential as a robust indicator of overall health and wellness.

Vidya Kamath, Ph.D., an associate professor at Johns Hopkins University School of Medicine, states, “The poor sense of smell has often been an early alert for diseases like Alzheimer’s and Parkinson’s, and even a mortality risk. This research emphasizes its link with depressive symptoms, and also investigates factors affecting the connection between smell and depression, including poor cognition and inflammation.”

The study analyzed data from 2,125 participants from the Health, Aging, and Body Composition Study (Health ABC). This group, consisting of healthy older adults aged 70–73 at the beginning of the research in 1997-98, underwent assessments for odor detection, depression, and mobility.

Initially, in 1999, 48% had a normal sense of smell, 28% had a diminished sense, known as hyposmia, and 24% experienced significant loss, known as anosmia. Those with a better sense of smell were generally younger, and 25% developed considerable depressive symptoms over time.

The researchers noted that those with reduced or significant loss of smell had a higher likelihood of showing depressive symptoms. Additionally, they identified three different patterns of depressive symptoms in the study group, and a weaker sense of smell was related to a greater chance of moderate or high depressive symptoms.

“Loss of smell impacts various health and behavior aspects, like detecting spoiled food or toxic gas and enjoying food. It might also be a sign of something wrong in your health, indicating late-life depression,” comments Kamath. “Smell plays a vital role in engaging with our surroundings, and this study reveals it may serve as a warning.”

The human sense of smell functions through specialized sensory cells in the nose, called olfactory neurons, which capture and relay molecules to the brain for processing. This mechanism works closely with brain areas controlling memory, decision-making, and emotions.

The Johns Hopkins team believes the connection between smell and depression may be influenced by both biological (like changes in serotonin levels and brain volume) and behavioral (such as decreased social interaction and appetite) factors.

The researchers plan to further validate their results in other groups of elderly adults and investigate alterations in olfactory bulbs to ascertain if they are indeed modified in those diagnosed with depression. They also intend to study how smell can be utilized in interventions to reduce the risk of late-life depression.

This research was a collaborative effort that included various scientists from institutions such as the University of Connecticut, University of California, San Francisco, National Institute on Aging, and Michigan State University. It received support from the National Institute on Aging, National Institute of Nursing Research, and National Institutes of Health’s Intramural Research Program.

No conflicts of interest were declared in relation to this research under Johns Hopkins University School of Medicine policies.