A Fragrant Memory

Tea olive trees smell of neither tea nor olives. Instead, the tiny, white blossoms smell like my great-grandmother’s yard in springtime, bursting with sweetness and warmth. They smell like summer on the patio in the house of my middle-school years, alluring and deceptively fresh in the South Carolina heat. And some mild winters, they smell like the first home I ever bought, comforting me among the newness of adulthood. A tea olives’ fragrance is so strong and specific that a breeze that catches it triggers memories as clear as an image on a new smartphone.

As the only cranial nerve that sees the outside world (yes, CN II, we get it, but that’s not what I meant), the olfactory nerve is now widely accepted as a key contributor to the creation of memories. In fact, increasing evidence has shown a correlation between the loss of the sense of smell and death from diseases of memory like Parkinson’s and dementia. A recent study in Annals of Internal Medicine by Liu and colleagues again showed this relationship and was the first to suggest a possible mechanism.

Like previous studies, the authors found that anosmia preceded dementia and Parkinson’s diagnoses as a type of “prodromal symptom” and in fact was more strongly correlated with mortality in patients whose health at baseline was reported as excellent or good. The patients, who were 70 to 79 years old and could walk a quarter-mile and up 10 steps without difficulty, were followed for 13 (!!) years. (I think my great-grandmother, who smelled of tea olives and looked like an angel with her halo of fine white hair, was bedbound nearing her 80s. I couldn’t imagine her walking to the end of her bedroom, let alone a quarter-mile to participate in a medical study!)

Liu and colleagues “found that poor olfaction was associated with 46% higher mortality at year 10 and 30% higher mortality at year 13 compared with good olfaction,” which was not explained by clinical or demographic confounders. They also showed no difference in olfaction-related mortality between sexes and races. Unlike previous studies, they also performed a mediation analysis to determine what associated variables might contribute and suggest a mechanism by which olfaction leads to dementia- and Parkinson’s-related mortality. Mediation analysis further suggested that 30% of the higher mortality may be due to dementia and Parkinson’s with weight loss.

The obvious correlation is that anosmia leads to decreased appetite. Food is not as appealing when it’s tasteless. Exceptions exist, of course. (For example: My middle school cafeteria served Frito pies—those deliciously terrible heart attacks in a bag that consisted of ground meat, cheese, and sour cream, in an opened bag of Frito Lay’s. The warm meat and the cool cream on the thick crunch might have convinced me to eat on days when my nose was too stuffy to really taste anything.) Even the study found that weight loss might be attributable to only 30% of that anosmic dementia and Parkinsonian mortality.

It is still unclear what that other 70% increase in mortality is due to, which means we’re still a far cry away from figuring out how to prevent the diseases or the anosmia that precedes them. At the very least, it’s a good reminder to stop and smell the tea olives.

Reference

1. Liu B, Luo Z, Pinto JM, et al. Relationship between poor olfaction and mortality among community-dwelling older adults: a cohort study. Ann Intern Med. 2019;170:673-681. [PMID: 31035288] doi:10.7326/M18-0775