Sense of Smell, While Poorer, May Help Patients in Enjoying Meals

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by Steve Bryson, PhD |

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Sniffin' Sticks | Parkinson's News Today | test of smells with Parkinson's | illustration of assorted herbs

People with Parkinson’s disease recognized food odors in a test called Sniffin’ Sticks better than they recognize the smell of natural spices used in food, a study showed.

They were less able to recognize smells than healthy individuals, but the work demonstrated that patients could identify selected scents.

These findings, its researchers noted, are a first step toward patient-appropriate approaches to enhance flavor, food enjoyment, and nutrition among people with Parkinson’s.

The study, “Odor Identification by Parkinson’s Disease Patients Tested by Using Sniffin’ Sticks versus Natural Spices,” was published in the journal Parkinson’s Disease.

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A poorer or absent sense of smell is a common non-motor symptom of Parkinson’s disease, and one that can occur many years before the onset of motor symptoms.

This loss can affect quality of life by increasing insecurities around personal hygiene and a lack of awareness for smells that raise risks, such as something burning or a gas leak. They can also affect a person’s ability to enjoy food or want to eat.

“Although previous studies showed odor identification deficits in [Parkinson’s disease] patients compared with age-matched healthy controls (HC), various studies also demonstrated that some odorants are still recognized by PD patients,” the research team with the Flanders Research Institute for Agriculture in Belgium wrote.

Sniffin’ Sticks is a validated test containing a variety of everyday smells that allows a semi-objective assessment of a person’s olfactory abilities, and one that can be used in olfactory training.

Researchers evaluated the identification of Sniffin’ Sticks odors compared with real-life spice odors in 80 adults with Parkinson’s and a group of 105 healthy adults. Both groups had a mean age of around 68 (range, 55 to 84), and patients’ disease duration had a mean of eight  years.

“This is the first study, to our knowledge, to evaluate real-life food odor identification in PD patients,” the team wrote.

Participants were asked not to smoke, eat, or drink — except for water — for one hour before the test. A 16-item Sniffin’ Sticks was used, with one of 16 fragrance pens given one at a time and people choosing what they were smelling from among four options presented. A correctly identified odor received a score of one point, with a total score ranging from zero to 16.

A score lower than eight was defined as anosmia (no sense of smell), between eight and 11 was hyposmia (reduced sense of smell), and a score above 11 was defined as normosmia (normal sense of smell).

Scores of the Sniffin’ Sticks test showed 73.8% of those with Parkinson’s had anosmia, 23.8% had hyposmia, and 2.5% had normosmia. In comparison, 21.9% of the control adults had anosmia, 43.8% had hyposmia, and 34.3% had normosmia.

No group differences were evident for scents of cinnamon, lemon, and pineapple, but other smells were better identified by healthy adults than patients.

In the Parkinson’s group, orange, peppermint, rose, and fish odors were best recognized, whereas apple, lemon, and coffee were least recognized. With control adults, orange, banana, rose, peppermint, fish, and leather odors were best recognized, while apple, lemon, pineapple, coffee, and cinnamon were the least recognized.

Statistical analysis revealed a lower mean Sniffin’ Stick score was significantly associated with a Parkinson’s diagnosis, male sex, and older age.

Across all participants, there was a nonsignificant trend toward an association between Sniffin’ Sticks scores and the use of antidepressant medication. Among healthy adults specifically, the researchers found  “an inverse association … between Sniffin’ Sticks test score and intake of anti-inflammatory medication and medication for high cholesterol levels.”

Among Parkinson’s patients, there was a trend toward an association between lower Sniffin’ Sticks scores and longer disease duration as well as a higher intake of Parkinson’s medications.

The spice odor test, which included 14 scents and one blank or no odor sample, was given to 34 adults with Parkinson’s and 53 control adults. There were no differences between groups for cardamom, rosemary, sage, oregano, marjoram, caraway, and the blank sample.

Garlic and blank were best recognized in Parkinson’s patients, while pepper, caraway, and mint were the least correctly identified. Among controls, the blank sample, garlic, cinnamon, and clove were the best identified odors, whereas oregano, caraway, and marjoram were the least recognized. Participants who correctly identified odors reported them as more familiar.

Across patients, lower spice odor test scores were significantly related to male sex and older age. For healthy adults, the spice test scores correlated with age only.

Among Parkinson’s patients who underwent both tests, the mean total Sniffin’ Sticks score was significantly higher than the mean total score of the spice odor test (40.8% versus 8.2%). Similar results were seen for controls (64.7% versus 29.7%).

“Our results showed that 97.6% of [Parkinson’s] patients had a reduced sense of smell (73.8% anosmic and 23.8% hyposmic),” the researchers wrote. “However, an overall association between pleasantness and identification, regardless of odorant, was found.”

People with Parkinson’s also clearly recognized “some food odorants, both Sniffin’ Sticks [and] natural odorants,” the researchers concluded, although “Sniffin’ Sticks odorants were better recognized compared with real-life odorants, by both [controls] and [Parkinson’s disease] patients.”

While no formal study has evaluated the use of aroma or flavor boosters for people with Parkinson’s, the use of familiar or preferred herbs or spices “may increase food enjoyment and food intake,” the team added, noting a need for more research.

“If such an intervention showed positive results … a patient-tailored approach may be useful to improve [patients’ quality of life] by diet optimization,” they wrote.