A surprising symptom that could be an early warning of Alzheimer’s disease is loss of smell, according to a new study. The study showed that this could be particularly prevalent among those people who have a specific genetic predisposition to Alzheimer’s.
The new study by researchers at the University of Chicago showed that people who carry the gene variant APOE e4, linked with an increased risk for Alzheimer’s disease, could lose their sense of smell first, signalling Alzheimer’s disease, according to Earth.com. This gene’s primary function is to transport cholesterol and other fats through the bloodstream.
The findings, published in Neurology, showed that the gene variant causes a decline of odour sensitivity earlier than odour identification or cognition. Hence, testing odour sensitivity could help predict future impaired cognitive function.
Notably, the study showed that reductions in odour detection can be observed between the ages of 65 to 69 but changes in the ability to identify the odour did not appear until the age of 75 to 79, according to Healthline. Furthermore, after losing the ability to identify odours, those with the gene variant also showed quicker loss of cognitive skills.
Loss of smell has become a familiar symptom since the Covid-19 pandemic, wherein many people affected by the disease temporarily lost their sense of smell. Loss of smell's connection with the brain has been studied by various studies. For instance, in April, a study by University College London, researchers found that individuals living with long Covid who suffered loss of smell showed different patterns of activity in certain regions of the brain, according to a press release. Another 2023 study, published in the journal EClinicalMedicine, has also shown that brain activities decline in people affected by Covid who have lost their sense of smell for a longer duration.
Talking about the link between loss of smell and early detection of Alzheimer’s, Dr Leah Alexander, a board-certified paediatrician in New Jersey told Healthline, “This may be due to the fact that olfactory neurons (or those that detect odours) are among the most vulnerable to damage from beta-amyloid, one of the proteins associated with Alzheimer’s disease.”
Alexander also added that the findings show how using loss of sense of smell as a warning sign can help people prevent further decline through lifestyle changes.