Losing sense of smell could be early symptom of Alzheimer’s, researchers find

Smell could be a “value added” diagnostic tool, says Charles Ramassamy, of the Institut national de la recherche scientifique.

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A change in a person’s sense of smell, including its disappearance, could be an early sign of the development of Alzheimer’s disease in the coming years, researchers believe.

“Studies have confirmed that the dysfunction of olfactory identification differentiates between people who are cognitively intact and those with a moderate cognitive deficiency or with Alzheimer’s disease,” says professor Charles Ramassamy, of the Institut national de la recherche scientifique.

In a first study published in 2013, scientists from the University of Florida measured at what distance their subjects could detect an odour of a jar of peanut butter with each nostril.

Those with probable Alzheimer’s disease had to get on average 10 centimetres closer with the left nostril than the right.

In 2020, Chinese researchers found that people with cognitive deficiencies or Alzheimer’s had lower odour detection scores.

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The proportion of subjects with an olfactory dysfunction was particularly high among those with Alzheimer’s.

The goal, Ramassamy said, is to see “just how far back we can go in time to detect this dysfunction, which could be predictive for the disease a few years, five or 10 years before the onset of Alzheimer’s disease.”

While the loss of a sense of smell is not unique to Alzheimer’s (it’s also a symptom of COVID-19, for example), it could be a “value added” diagnostic tool, he said.

Only 11 per cent of patients with moderate cognitive problems but without olfactory dysfunction, eventually contract Alzheimer’s disease.

The dysfunction is believed to be related to changes in the brains of patients with Alzheimer’s. Imaging studies showed, for example, that the brains of patients with undiagnosed Alzheimer’s but who have olfactory dysfunction had similar changes to those of patients where the disease was diagnosed.

“The changes in the brain could begin 10, 20, 30 years before the first symptoms,” Ramassamy said. “The more we can identify early markers, the more we can turn on this little red light that will tell us to pay attention.”