Losing sense of smell may signal onset of dementia in older adults, says study

New Delhi: Dementia is the most common forms of Alzheimer's disease and is an age-related mental condition, triggered by loss of memory and outlined with rapid and seemingly unprovoked mood swings and unecessary aggression.

Over the years, scientists have studied the disease thoroughly and have often found signs other than loss of memory that can signal the onset of dementia.

A new study, conducted by researchers at University of Chicago in the US, has found that loss of the sense of smell is one of those unfortunate signs.

According to the study, older adults who have trouble identifying common odours are more than twice as likely as those with a normal sense of smell to develop dementia within five years.

Researchers conducted a long-term study of nearly 3,000 adults, aged 57 to 85 years.

They found that those who could not identify at least four out of five common odours – peppermint, fish, orange, rose and leather – were more than twice as likely to develop dementia within five years.

The team found that although 78 percent of those tested were normal – correctly identifying at least four out of five scents – about 14 percent could name just three out of five.

Five per cent could identify only two scents, two percent could name just one, and one per cent of the participants were not able to identify a single smell.

Researchers noted five years after the initial test, almost all of the study subjects who were unable to name a single scent had been diagnosed with dementia.

Nearly 80 percent of those who provided only one or two correct answers also had dementia, with a dose-dependent relationship between degree of smell loss and incidence of dementia.

"Loss of the sense of smell is a strong signal that something has gone wrong and significant damage has been done," said Jayant M Pinto, professor at the University of Chicago.

The study, published in the Journal of the American Geriatrics Society, used a well-validated tool, known as "SniffinSticks."

These look like a felt-tip pen, but instead of ink, they are infused with distinct scents. Study subjects smell each item and are asked to identify that odour, one at a time, from a set of four choices.

The five odours, in order of increasing difficulty, were peppermint, fish, orange, rose and leather.

Researchers noted that 78.1 percent of those examined had a normal sense of smell, 48.7 percent correctly identified five out of five odours and 29.4 percent identified four out of five.

They noted that 18.7 percent, considered "hyposmic," got two or three out of five correct and the remaining 3.2 percent, labelled "anosmic," could identify just one of the five scents or none.

The olfactory nerve is the only cranial nerve directly exposed to the environment, researchers said.

The cells that detect smells connect directly with the olfactory bulb at the base of the brain, potentially exposing the central nervous system to environmental hazards such as pollution or pathogens. Olfactory deficits are often an early sign of Parkinsons or Alzheimers disease.

They get worse with disease progression, researchers said.

(With PTI inputs)