Smelling Alzheimer's Disease with Peanut Butter

Scientists have found a way to detect Alzheimer's disease using a patient's sense of smell.

Marsha Lewis, Contributing Producer

(Inside Science TV) -- Some like peanut butter creamy; others like it crunchy, with a little jelly, or straight out of the jar. But scientists have recently discovered that the classic spread could help detect early Alzheimer's disease symptoms.

Once fully validated, the peanut butter test could provide a cheap, rapid test for Alzheimer’s disease, a form of dementia that affects as many as 5 million Americans. "You need a ruler and some peanut butter, and that's it," said Jennifer Stamps, a neuroscientist at the University of Florida in Gainesville, FL.

Alzheimer’s disease is perhaps most infamous for its cruel toll on thought, language and memory, but "your olfactory cortex, the part of the brain that processes smell, is the first area of the brain to deteriorate in Alzheimer’s," Stamps said. Scientists first started researching the relationship between smell and Alzheimer’s in the 1980s, with the hopes that odors could help with early diagnoses. But using peanut butter could make these tests cheaper and perhaps even more effective. For one, "peanut butter is not a smell lost during typical aging," said Stamps. It’s also a complex odorant, containing hundreds of types of molecules that exclusively trigger the nerves leading to the olfactory cortex.

After ruling out other problems such as prior sinus infections – which could damage a person’s sense of smell – Stamps says that in less than two minutes, she can determine if there is a problem with the olfactory cortex. First, the patient is blindfolded and holds one of their nostrils closed. Stamps then holds up a ruler beside the patient's open nostril and places an open sample of peanut butter on the bottom of the ruler, twelve inches from the patient’s nose. She then slowly raises the sample until the patient detects the odor and measures the distance between the peanut butter and the patient's nostril. The test is then repeated with the other nostril.

Differences between the left and right nostrils’ sensitivity are normal, but a large difference may be an early indication of Alzheimer's. In a 2013 study co-authored by Stamps, she found that 18 patients who likely had Alzheimer’s disease couldn’t smell peanut butter out of their left nostrils until the samples were only 5 cm (2 inches) away, some 12 cm (5 inches) closer than samples under their right nostrils.

While this test isn't the first to use smell to diagnose early-stage Alzheimer's – and bigger evaluations of the test are needed – it has been very accurate thus far.

"The sensitivity is 100 percent in the early Alzheimer's group," said Stamps. The peanut butter test also might help correct false diagnoses of Alzheimer’s, she said. "We get a lot of patients in our practice that are told they have Alzheimer’s, and a lot of times they don’t."

Even though there is currently no cure for Alzheimer's, confirming a diagnosis early could be life-changing. "I think it would be something that you could easily do in a geriatric practice that might make you look harder at their lab work," said Stamps, and hasten the treatment of Alzheimer’s symptoms. “The sooner you slow down the progression, the better."