The research, published in the Journal of the International Neuropsychological Society, is the first of its kind to focus on self-reported olfactory impairment in healthy aging people before the onset of dementia.
“Our study is important because it shows that self-reported olfactory impairment can be an early sign of, for example, Alzheimer’s disease. Earlier studies have implied a connection between olfactory impairment and dementia but have not looked at how people experience their own sense of smell,” said lead author Ingrid Stanciu, postgraduate student at Stockholm University.
The study followed 1,529 people for a 10 year period. During that time, 159 of them would eventually develop dementia. The risk of dementia was affected by information provided at the beginning of the study such as older age, reduced cognitive ability, and objective and subjective olfactory impairments.
It is important to note that most people who experience a diminished sense of smell do not go on to develop dementia, even when their risk is elevated. Olfactory impairment should be thought of as only one risk factor when making an evaluation of the risk of dementia.
“We believe that self-reported olfactory impairment should be complementary to other factors when the risk of developing dementia is evaluated. Future studies must go further and, among other things, examine which olfactory evaluation procedures are most useful to evaluate the risk of dementia,” said Stanciu.
Several types of dementia are associated with an impaired sense of smell. This study is the first to link both objective olfactory problems (performing poorly in a smell test) and subjective olfactory problems (to experience a less sensitive sense of smell than normal) to a diagnosis of dementia within 10 years.
Source: Stockholm University