"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," says Ingrid Stanciu, postgraduate student at Stockholm University and main author of the study.
Common forms of dementia often result in an impaired sense of smell. Researchers from Stockholm University are the first to have linked both objective olfactory impairment (i.e. performing under par in a smell test) and subjective olfactory impairment (to experience a less sensitive sense of smell than normal) to a diagnosis of dementia within ten years.

"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," says Ingrid Stanciu.

It is important to note that most people who experienced an olfactory impairment did not get dementia, even though their risk was elevated. Olfactory impairment should therefore be regarded only as a complementary measurement when making an evaluation of the risk of dementia.

In the study 1,529 people were followed during a ten-year period. During those ten years, 159 participants developed 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. The results were recently published in the Journal of the International Neuropsychological Society.