A Smell Test Plus a Memory Check Predicted Decline Nearly as Well as Brain Scans

CATEGORY: BRAIN & MENTAL HEALTH

A scratch-and-sniff card paired with a short memory quiz predicted who would go on to cognitive decline or dementia about as accurately as MRI and PET brain scans did. The two tests take minutes and cost almost nothing. The scans cost thousands and need specialized equipment. That comparison comes from a 2024 study that followed 647 older adults for about eight years.¹

Smell Nerves Run Into the Rooms Alzheimer’s Enters First

The nerves carrying smell information feed into the same brain regions where the earliest changes of Alzheimer’s tend to appear, including the areas handling memory. So a fading ability to name everyday odors can surface years ahead of obvious memory trouble. That is what makes smell a usable early window on brain health.

647 Adults, Eight Years, Both Kinds of Test

Participants came from the Mayo Clinic Study of Aging. At the start, each took a 12-item Brief Smell Identification Test, a scratch-and-sniff card that runs about five minutes, along with a short cognitive test. Each also underwent MRI and PET scans capable of detecting Alzheimer’s-related changes. Then the researchers waited. Over an average of roughly eight years, 102 participants developed cognitive decline and 34 developed dementia.¹ The question was which baseline measures had called it. The cheap pair did about as well as the imaging, and the authors wrote that a short odor-identification test alongside a quick cognitive screen deserves attention as a practical, affordable way to flag people at higher risk.¹

A Low Score Is Not a Diagnosis

Smell fades for plenty of ordinary reasons. Colds, allergies, sinus problems, a past COVID-19 infection, certain medications, plain aging. A poor score on an odor test does not mean dementia is present or on the way. It is a screening signal, not a verdict, and the wider evidence sets bounds on how far the signal reaches. Pooling eight studies of 13,165 older adults, people with impaired smell were about 2.4 times as likely to later develop cognitive decline or dementia, though the link was strongest in the 60s and 70s and no longer clear past 80.² A Swedish study of 2,418 adults followed for 12 years likewise tied shortened smell-identification tests to higher dementia risk.³

Key Takeaways

• A five-minute scratch-and-sniff test paired with a brief memory check predicted later cognitive decline and dementia about as well as MRI and PET imaging did in this study of 647 adults.
• What the tests pick up is a lasting decline in identifying familiar smells, not the temporary loss that comes with a cold, allergies or a stuffy nose.
• Smell loss has many harmless causes, and a low score is not a diagnosis.
• Across eight pooled studies, impaired smell carried roughly 2.4 times the likelihood of later decline, though the link was no longer clear past age 80.

References

1. Devanand DP, Lee S, Luchsinger JA, Knopman D, Vassilaki M, Motter JN. Comparison of brief olfactory and cognitive assessments to neuroimaging biomarkers in the prediction of cognitive decline and dementia in the MCSA cohort. Alzheimers Dement. 2024 Dec;20(12):8346-8358. link
2. Chen Z, Xie H, Yao L, et al. Olfactory impairment and the risk of cognitive decline and dementia in older adults: a meta-analysis. Brazilian Journal of Otorhinolaryngology. 2021;87(1):94–102. link.
3. Dickmänken E, Larsson M, Ekström I, et al. Odor identification and progression to dementia: the role of odor characteristics and set size. Alzheimer’s & Dementia: Diagnosis, Assessment & Disease Monitoring. 2024;16(4):e70035. link.