Losing Sense of Smell Puts Elderly at Risk of Dementia, Study Finds

Losing your sense of smell as you age could mean you’re at greater risk of developing dementia, according to a new study.

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The results of a long-term study of nearly 3,000 older adults found that those who couldn’t identify at least four out of five common odors were more than twice as likely as those with a normal sense of smell to develop dementia within five years.

“These results show that the sense of smell is closely connected with brain function and health,” said Dr. Jayant Pinto, a co-author of the study and professor of surgery at the University of Chicago, in a statement. “We think a decline in the ability to smell, specifically, but also sensory function more broadly, may be an important early sign, marking people at greater risk of dementia.”

For the study, 2,906 adults between the ages of 57 and 85 smelled five felt-tip pens, each infused with a distinct odor: peppermint, fish, orange, rose or leather. Participants were asked to identify each odor from a set of four choices.

Although 78 percent of participants were found to have a normal sense of smell – correctly identifying at least four out of five odors – about 14 percent could identify just three out of five odors, 5 percent could identify only two scents, 2 percent could name just one, and 1 percent could not identify a single odor. 

Five years after initial testing, results revealed a relationship between the degree of smell loss and incidence of dementia, with increased loss of smell corresponding with a greater probability of participants being diagnosed with dementia.

“Loss of the sense of smell is a strong signal that something has gone wrong and significant damage has been done,” Pinto said. “We need to understand the underlying mechanisms, so we can understand neurodegenerative disease and hopefully develop new treatments and preventative interventions.”

The olfactory nerve is the only cranial nerve directly exposed to the environment. The cells that detect smells connect directly with the olfactory bulb at the base of the brain, which could potentially expose the central nervous system to environmental hazards, such as pathogens or pollution.

The olfactory system also has stem cells which regenerate, meaning “a decrease in the ability to smell may signal a decrease in the brain’s ability to rebuild key components that are declining with age, leading to the pathological changes of many different dementias,” said study co-author Martha K. McClintock, a psychology professor at the University of Chicago, in a statement.

Deficits in sense of smell are often an early sign of Parkinson’s or Alzheimer’s disease. “This simple smell test could provide a quick and inexpensive way to identify those who are already at high risk,” Pinto said, adding more research is needed to consider it a clinical test. “But it could help find people who are at risk. Then we could enroll them in early stage prevention trials.”

Follow Kristen Thometz on Twitter: @kristenthometz

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