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

CATEGORY: BRAIN & MENTAL HEALTH

Your sense of smell is wired directly into brain regions that Alzheimer’s disease attacks early—which is why losing it can be an early warning sign. A 2024 study found that a quick, inexpensive scratch-and-sniff test, combined with a brief memory check, predicted future cognitive decline and dementia about as well as costly brain scans.¹

Smell Nerves Feed Brain Areas Alzheimer’s Hits First

The nerves that carry smell information feed into the same parts of the brain—including the areas handling memory—where the earliest changes of Alzheimer’s tend to appear. Because of this, a fading ability to identify everyday odors can show up years before obvious memory problems, making smell a useful window into brain health.

647 Older Adults Followed for Eight Years

Researchers in the Mayo Clinic Study of Aging followed 647 older adults for an average of about 8 years. At the start, each person took a 12-item Brief Smell Identification Test—a roughly 5-minute scratch-and-sniff card—along with a short cognitive test, and also underwent expensive MRI and PET brain scans that detect Alzheimer’s-related changes. The researchers then tracked who went on to develop cognitive decline or dementia.¹ During follow-up, cognitive decline developed in 102 participants and dementia in 34.¹

Two Low-Cost Tests Matched Scans Costing Thousands

The combination of the brief smell test and the brief cognitive test predicted who would decline about as accurately as the high-tech brain imaging. In other words, two simple, low-cost tools performed comparably to scans that can cost thousands of dollars and require specialized equipment. The authors concluded that pairing a short odor-identification test with a quick cognitive screen deserves consideration as a practical, affordable way to flag people at higher risk.¹

Colds, Allergies and Medications Also Dull Smell

A poor smell-test score does not mean you have or will get dementia. Smell fades for many ordinary reasons—colds, allergies, sinus problems, past COVID-19 infection, certain medications, and normal aging. This research points to smell testing as a low-cost screening signal that can help identify who might benefit from closer follow-up, not as a stand-alone diagnosis. The promise is earlier, cheaper risk detection—which matters most now that treatments work best when started early.

Impaired Smell, 2.4 Times the Risk in 13,165 Adults

The broader evidence backs the link but narrows it. A meta-analysis of eight studies covering 13,165 older adults found that people with impaired smell were about 2.4 times as likely to later develop cognitive decline or dementia—though the association was strongest in the 60s and 70s and was no longer clear past age 80.² A Swedish study following 2,418 adults for 12 years likewise linked shortened smell-identification tests to higher dementia risk.³

Key Takeaways

• Simple, inexpensive smell and memory tests may flag cognitive risk nearly as well as costly brain scans, making early screening more accessible.
• The tests looked at a noticeable, 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, so a low score is a prompt for follow-up, not a diagnosis.

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.