Read with care: when scientific research is NOT evidence for essential oil therapeutic effects.

By E Joy Bowles, PhD, BSc Hons.
As a scientist, I have mixed feelings about the way scientific research is being used to support the claims for essential oil use. On the one hand, I am delighted that essential oil users are curious about how their oils work, and are keen to seek out more information. On the other hand, I am alarmed that they are happy to settle for summaries of research and claims made in abstracts without going to the source articles or reading the full papers to double-check the claims made.
As an example, two papers have come to my attention recently, both posted on Facebook by well-meaning essential oil enthusiasts.
 
Valid or invalid: exposure to essential oils for more than 1 hour may be harmful to cardiovascular health?
A report in the European Journal of Preventive Cardiology “The effect of essential oil on heart rate and blood pressure among solus por aqua workers” published in 2014 claims in the abstract “Prolonged exposure for longer than 1 hour to essential oils may be harmful to cardiovascular health among spa workers”. The person posting it on Facebook was alarmed, and wanting to caution their friends about using essential oils safely.
 
Their trial involved 100 healthy young spa workers inhaling vaporised Bergamot oil over a 2-hour period, and having their blood pressure taken every 15 minutes. The experiment was repeated 3 times, and there were no statistically significant results between the results from each occasion. Initially participants experienced a small decrease in mean systolic and diastolic blood pressure and pulse rate, but in the measurements taken during the second hour of the experiment, they experienced a small increase in means for these measures, compared to baseline. The mean decrease in systolic BP was -2.1 mmHg (at the 45-minute measure), the mean increase was + 2.19 mmHg (at the end of the 2 hours).  
 
However, there was no control group, so there is no way of knowing whether the changes in BP were due to the Bergamot oil, or not. Conceivably, people’s BP could drop just by sitting still for 45 minutes, and could rise again as they got stressed by being bored during the second hour!
 
In their discussion, although they acknowledge that “it is still unknown whether small, short-term fluctuations of BP and HR are associated with a higher risk of clinical cardiovascular diseases even if elevated BP and HR can serve as markers for increased risks of cardiovascular diseases”, they go on to make their unfounded statement that prolonged exposure may be harmful to cardiovascular health.  And the title and abstract claim the research is about “essential oils” in general rather than Bergamot essential oil specifically.
 
So, in my opinion, the conclusions are invalid, and the article should not be shared as evidence of effects of essential oils on human health.
 
Valid or invalid: Essential Oils can help ADHD?
The other shared article titled “Essential Oils Can Help ADHD” posted on the internet by osteopath Dr Joseph Mercola claims that “Research by the late Dr Terry S. Friedmann, a physician who believed in treating the body, mind and spirit as one, showed that vetiver oil was beneficial for children with ADHD.”
On reading the paper by Dr Friedmann (not from a peer-reviewed scientific journal, just from a Meetup website), it turns out that Dr Friedmann’s conclusions about vetiver were based on 4 subjects only, and fails to mention whether the changes in beta-theta wave ratio that he observed were measured while the subjects were being challenged with a task requiring focused attention or not. Dr Friedmann also fails to comment on the fact that the 16 children in the control group (who had no essential oil treatment) also experienced positive changes in their beta-theta wave ratios. It is not valid to make claims of a generalisable therapeutic effect based on results from just 4 subjects.

The other papers Dr Mercola cites as possible evidence for Vetiver being good for ADHD are from an experiment done on sleep-wake hours in rats exposed to vaporised vetiver oil, and one done on alertness of 18 adults without ADHD exposed to vapour from fresh roots of vetiver, not the essential oil!

It would be great if there really was evidence that inhaling essential oils had measurable effects on focus in children with ADHD. However, none of these articles provide sufficient evidence for me. I would not share any of these articles as evidence that essential oils help ADHD.

How to determine quality of a scientific paper
To determine the quality of a scientific paper, two things need to have been done: firstly, the trial needs to have been designed and carried out appropriately; secondly, the report needs to contain sufficient detail for readers to be able to fully understand the trial design, results, discussion and conclusions, including any limitations noted by the authors.
Essential oil users wanting to find out if a scientific paper provides real evidence to support therapeutic claims for an essential oil need to become “quality detectives”. The first question to ask is “Is the full-text available anywhere, rather than just the abstract?” Try Google Scholar or Research Gate, https://www.researchgate.net/ where a lot of researchers publish pre-print versions of their articles.
Once you have the full-text ask these questions:

• Does the report clearly identify the nature of the participants (including age, sex, health condition measures, any inclusion or exclusion criteria)
• Was there a control group who had everything done to them in the same way, except having the essential oils, and was there also a no-treatment group who were only measured at the start and the end?
• How many people received the treatment? If it was fewer than 30 people, it’s unlikely the results can be generalised. Preferably there should be at least 100 people receiving the treatment, especially if the effect size of the treatment is small.
• Were baseline measures taken, and were the descriptive statistics of each of the groups of people in the trial the same (mean, standard deviation of the mean, range and distribution of values), or at least not significantly different when compared statistically?
• Is the dose reported adequately?
• Is there a listing of the botanic name and percentage of essential oil constituents in the oil(s) used in the trial?
• Were the tests or scales used the best ones that could have been used (gold standard, or at least widely accepted and used in medical/ nursing research?)
• Do the results make sense clinically, if it’s a clinical effect being researched? A statistically significant result does not necessarily mean a clinically significant result (as in the second paper discussed above).
• When you read the paper and look at the results tables, are there any unanswered questions you have about how the trial was done, and what the results really mean?

The need for rigour in design and reporting applies to all forms of scientific research, not just complementary therapies research. The CONSORT group (CONsolidated Standards Of Reporting Trials) is an independent body of researchers that has developed checklists and guidelines for researchers to use to ensure their research design and reporting is of good quality. There are several variants of the original CONSORT statement, including one on non-pharmacological treatments (which aromatherapy trials usually fit into).
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My dream is to have people using essential oils become scientifically literate enough to critically evaluate scientific papers themselves. Maybe we could start a journal club, where we go through various papers on aromatherapy/ essential oils and critique them as a group?
​Please contact me if you’re interested @DrEJoyB or [email protected]