As we get older, our memory declines. What if I told you there was now a “simple” and “easy” successful method to boost your memory, the result of research from genuine scientists at a university which has produced five Nobel laureates? One of the researchers is even the former associate dean of undergraduate education. With those credentials in tow, you might just believe me.
The findings from this study were published last July, and its university’s press office released a whopper of a write-up, saying participants’ memories “skyrocketed” following the intervention. Is it a miracle pill or a memory-boosting game for your smartphone? No. It’s the wafting of essential oils for two hours each night.
Reading the hyped-up press release, I am reminded of the carnival barker whose job is to sell tickets by stretching the truth. A person missing both arms is described as the Seal Man; the dried carcass of a ray is declared to be a basilisk whose glance would kill you on the spot. So much fanfare for such a limp reality.
The link between our sense of smell and neurological conditions is very real and fascinating. This latest study on essential oils, though? Not worth the razzmatazz of the carnival barker.
Smells like a warning
Odours can be powerful triggers for distant memories, a fact which is sometimes referred to as the Proust phenomenon. French novelist Marcel Proust famously described in his book Swann’s Way how eating a piece of madeleine cake dipped in lime-blossom tea flooded his narrator’s mind with childhood memories. (Interestingly enough, the specifics were altered during drafting of the novel’s manuscript, from toasted bread mixed with honey to the now-legendary and very French madeleine and tea mix.)
There is also a strange and persistent connection between olfaction and brain problems, which often goes unremarked. Losing your sense of smell can be an early warning sign for a variety of neurological conditions like Alzheimer’s disease and Parkinson’s disease. This change may be perceived as affecting not smell but taste: that’s because the distinct taste of what we eat and drink is often dictated by volatile molecules that float, as we swallow, from the back of our throat to our nose. Actual taste is limited to sweet, sour, bitter, salty and savoury, and to detecting textures like chalkiness and qualities like the metallic sting of blood.
Not everyone who partially loses their sense of smell is bound to develop a neurological condition like dementia, however. Over half of people between the ages of 65 and 80 see their sense of smell altered, and that fraction goes up to three quarters for those over the age of 80. It is, unfortunately, a common consequence of aging. There are also other culprits besides aging and neurological conditions, like respiratory infections such as COVID-19.
But this loss of smell as an early warning sign for brain disorders is not to be ignored. For Alzheimer’s disease, this olfactory impairment is progressive and often happens early on. It can be seen in over 90% of patients. In Parkinson’s disease, smell dysfunction is common and relatively stable, regardless of the stage of the disease. It also occurs in over 90% of patients and often appears years before the disease starts to affect movements. This peculiar symptom has also been tied to other disorders, such as Down syndrome and Lewy body disease.
And it has been associated with a higher rate of death in multiple studies, although it is not fully clear exactly what is happening here. As we get older, we tend to lose the full use of our nose and we get closer to death, so an association between the two is to be expected. But in one study, an impoverished sense of smell was specifically tied to more deaths due to neurodegenerative and cardiovascular diseases. More studies, as always, are needed.
Given this association between loss or altered smell with disease and death, we are left wondering if there is a way to preserve our sense of smell as we get older. And that’s where this latest study on aromatherapy comes in. There is evidence that olfactory enrichment—meaning to surround yourself with different smells—improves brain activity in both laboratory animals and humans.
Thus, the idea that smelling different essential oils as we fall asleep might act as a sort of tonic for the brain to ward off memory loss.
But what did this study actually show?
Results that fail the smell test
The researchers behind the trial, which comes out of the University of California, Irvine, gave older adults with no diagnosis of cognitive impairment an aroma diffuser. Each night, these adults would fit the diffuser with a specific vial that contained one of seven undiluted essential oils, one for each night of the week: rose, orange, eucalyptus, lemon, peppermint, rosemary, and lavender. When they went to sleep, the diffuser would release one aroma into the air for two hours before shutting down. The idea was to enrich their lives with these seven smells to keep the brain active, and a different scent each night was meant to register as “new” in the brain, to keep it engaged. Participants who were randomized to the control group instead received vials of mostly water, with barely any essential oil in them. The entire study lasted six months.
The press release claims that the participants who got to smell the undiluted essential oils “reaped a 226% increase in cognitive capacity compared to the control group.”
In reality, four tests were administered to the participants both before the experiment began and at the end of it. They were given strings of numbers which they had to repeat in the same order (e.g. 4-2-9-1). They were given strings of numbers which they had to repeat backwards (e.g. 3-8-4-2 becomes 2-4-8-3). They were given series of letters and numbers all mixed up and had to repeat them, with the letters now in alphabetical order followed by the numbers in ascending numerical order (e.g. 21-B-11-X becomes B-X-11-21). Allow me to be clear: there was no difference on any of these tests between the essential oil group and the control group.
In the fourth test, a researcher read out a list of 15 words to each participant, who was asked to repeat them back in any order. The same list was read a second, third, fourth, and fifth time, and each time the participant had to remember the words and recall as many as they could. On the fifth trial—and only on the fifth trial—the people in the essential oil group did better than those in the control group.
How many were in each group, you may be wondering? While an early registration of the study shows the aim was to recruit 200 people, 43 people were recruited initially. Then, the COVID-19 pandemic interrupted the study and forced the scientists to follow up with the participants virtually. Compliance was variable. In the end, when it came time to calculate which group did better on these cognitive tests, data from only 23 participants was used: 12 in the essential oil group and 11 controls.
To refer to this lackluster finding—that 3 of 11 controls improved versus 6 of 12 people exposed to essential oils on the fifth trial of only one of four cognitive tests—as “memories skyrocketed,” transforming the link between smell and memory “into an easy, non-invasive technique for strengthening memory and potentially deterring dementia,” as the press release does, borders on impropriety. This finding is very much in keeping with what you expect to find by chance alone. Test small enough groups of people for enough variables and you are bound to find an association through the roll of the dice.
There have been other attempts at showing that aromatherapy can help with memory, and there too the quality is inadequate. A 2014 review on the use of sage demonstrates significant deficiencies in sample size, study design, and transparency. A 2020 review on rosemary erroneously lists studies done in animals—the totality of the evidence looked at—as “clinical studies,” a term only meant for human experimental data. As for lavender, two studies were identified by a 2022 review. They lacked proper blinding, did not recruit many participants, and came to opposite conclusions.
As Rachel Herz, who holds a doctorate in psychology and is an expert on the psychology of smell, remarked in her review article on the role that odour-evoked memories play on our health, the potential that smells have to be used as therapy “is not a testament to aromatherapy,” which has been mostly unsuccessful “due to a lack of scientific rigour and confusion regarding the mechanisms involved.” Sure, the scent of vanilla or lavender wafting through your house may be pleasant and temporarily improve your mood, but it’s unlikely to ward off dementia.
The problem with hype, though, is that it accelerates the separation of consumers from their hard-earned cash. The UC Irvine study has a commercial angle. It was funded by Procter and Gamble, the American multinational whose brands include Febreze, Olay, Ivory, Old Spice, and Herbal Essences. Two of the study authors declare having received travel expenses and compensation from the multinational for presentations they made there, and four employees of Procter and Gamble are thanked by name in the paper “for their support and helpful discussions.”
The press release tells the rest of the story: “A product based on their study and designed for people to use at home is expected to come onto the market this fall.” The scientists noted in their paper a limitation: that the diffuser could only release a single scent each night. I guess Procter and Gamble have designed a solution.
So, there we have it. I can already hear the crisp voice of the carnival barker grabbing our attention this coming autumn: “Help maintain your healthy brain function in old age with this simple trick! A state-of-the-art machine, backed by real science, tickles your brain with seven smells at night! Rosemary! Peppermint! Lavender! Boost your memory! Restore your senses! Support your brain! Step right up!”
Take-home message:
- Loss of or altered smell can be an early sign of neurological disease like Alzheimer’s disease and Parkinson’s disease, although it is also commonly seen with old age and can be triggered by other factors, like a respiratory infection
- A study from UC Irvine claims to show that smelling essential oils at night dramatically improves memory, but the study was tiny and the improvement was only seen on the fifth trial of only one of four cognitive tests
- The study was funded by the multinational Procter and Gamble, which is reported to be releasing an essential oil diffuser this fall based on these mediocre findings
