One of the main reasons I wanted to start this blog was to give myself a reason to research topics in the field of food and nutrition that I’m genuinely interested in, and take a look at some traditional beliefs about nutrition and examine if they are accurate or not. Hopefully I’ll find out some interesting things and be able to share them with you in a digestible way!
Although slightly outside of the realm of nutrition and dietetics, a topic I’ve been interested in for the last couple of months is the therapeutic effects of certain plants, as used in herbal medicine. Herbal medicine has been around for thousands of years, and I’ve assumed that the plants used in herbal medicine have stuck around because they do provide some therapeutic effects (even if the mechanisms of why are not fully understood). However, I haven’t considered if there are any scientific studies out there to back up anecdotal and observational claims - or if any benefits are only a placebo.
I figured the easiest way to approach this subject (as someone with no background in herbalism) was to pick one herb to examine at a time, reviewing the literature and seeing whether there is evidence of therapeutic effects. And so we get the topic of this blog post: rosemary!
Traditionally, rosemary has had a wide range of use cases, from improving memory to reducing pain and anxiety (Grieve, 1931).
We probably know rosemary best as a culinary herb, but did you know that it also has a long history as a medicinal herb too? Traditionally, rosemary has had a wide range of use cases, from improving memory to reducing pain and anxiety (Grieve, 1931). Interestingly another historical use of rosemary was to stimulate hair growth and prevent early baldness - and rosemary oil as a hair-growth treatment remains one of the most popular non-culinary uses of rosemary today!
As I wrote earlier, I like to think that plants have been used as medicine because they do contain some therapeutic properties (even if the mechanisms weren’t understood or have been exaggerated in historical texts). To start my investigation, I looked at existing scientific literature to see if there are any texts out there to back up (or contradict) these claims. I was pleasantly surprised to see that there is a decent amount of recent research into the medicinal attributes of rosemary and other plants, showing that sections of the scientific community are keen to investigate herbal and traditional medicines.
However, a lot of the research I found is in early stages, with many studies conducted on animals or cultured cells. These types of study aren’t applicable to humans (due to the incredibly complex way in which our bodies work), but positive results from these studies definitely support further research in the area.
Most research on rosemary has narrowed down the most potent active compounds to rosmarinic acid and carnosic acid (with oleanolic acid, caffeic acid and several others also being of note).
I’ve discussed a couple of common traditional use cases of rosemary below (effects on memory/brain health, and stress and anxiety relief), to investigate whether there’s scientific research that supports these uses.
There are many more purported benefits of rosemary - I may do a follow-up blog post to discuss other therapeutic properties of rosemary and any scientific literature on those topics!
Memory
In Ancient Greece, students used rosemary to help them study and prepare for exams (both eating the herb and wearing garlands made from it). Rosemary’s reputation for improving memory has persevered to today and some researchers are investigating the effects of rosemary on brain health. A study published in Phytomedicine in 2018 found that taking an extract of rosemary, sage and lemon balm for two weeks improved delayed memory recall (recalling a list of words ten minutes after initially seeing them) in adults under 62 (Perry et al, 2017). Granted, this study is not without its limitations - the sample size was small (44 participants in total) and the results initially showed no improvement in the test group before the analysis was made age-range specific. But these tentatively positive results for the brain-protective function of these herbs definitely warrant further research in the area.
Several other studies on mice and rats have found memory and brain-protective functions of rosemary - although interesting it is important to remember that research on animals can’t be directly applied to humans without further research (Rahbardar and Hosseinzadeh, 2020).
Stress and anxiety relief
Rosemary is often traditionally used as a calming agent. A study on rats found that those who had been injected with rosemary extract were less anxious and stressed when placed in a stressful situation compared to a control group receiving no treatment. The rats who received high doses of rosemary exhibited anxiety and stress reducing effects similar to diazepam (De Oliveira, Camargo, and De Oliveira, 2019).
The exact method by which rosemary (or compounds within rosemary) can reduce stress is unknown. In a review of the literature on rosemary’s therapeutic effects on nervous system disorders, Rahbardar and Hosseinzadeh (2020) highlighted a mouse study that tentatively proposed that rosemary (in essential oil form) modulates the hypothalamus-pituitary-adrenal (HPA) axis.
Separate from either of the therapeutic uses of rosemary discussed earlier, another interesting journal article I read discusses how rosmarinic acid and carnosic acid (two active compounds within rosemary) have the ability to distinguish between very specific ion channels in the central nervous system (Manville, Hogenkamp & Abbott, 2023). This class of ion channels help to moderate when action potentials are fired in the brain - when one brain cell is stimulated enough to send a message on to the next cell. The exact role of the ion channels that the rosemary compounds interact with is not fully known, but not many molecules have this much specificity for one class of ion channel. It’s therefore pretty interesting that a naturally occurring compound in a common plant is able to interact with the parts of the nervous system in such a specific way. Although the mechanisms are far from known, it is easy to hypothesise that this could partially explain why rosemary has traditionally been used to treat and soothe conditions linked to the brain and nervous system.
From my research, I’m pleasantly surprised that there has been scientific investigation into therapeutic uses of rosemary, even if studies are small scale or on animal or cultured cells. It amazes me at how resourceful humans in the past were - identifying through trial and error which plants are best for treating which conditions and passing down the knowledge through generations all the way to today.
References
Grieve, M. (1931) A Modern Herbal. Available at: https://botanical.com/. (Accessed 26 July 2023).
Perry, N. S. L., Menzies, R., Hodgson, F., Wedgewood, P., Howes, M. J. R., Brooker, H. J., Wesnes, K. A., and Perry, E.K. (2017) ‘A randomised double-blind placebo-controlled pilot trial of a combined extract of sage, rosemary and melissa, traditional herbal medicines, on the enhancement of memory in normal healthy subjects, including influence of age’, Phytomedicine, 39, pp. 42-48.
Rahbardar, M. G. and Hosseinzadeh, H. (2020) ‘Therapeutic effects of rosemary (Rosmarinus officinalis L.) and its active constituents on nervous system disorders’, Iranian Journal of Basic Medical Sciences, 23(9), pp. 1100-1112.
Manville, R. W., Hogenkamp, D. and Abbott, G. W. (2023) ‘Ancient medicinal plant rosemary contains a highly efficacious and isoform-selective KCNQ potassium channel opener’, Communications Biology, 6(644), published online. doi: 10.1038/s42003-023-05021-8.
De Oliveira, J.R., Camargo, S.E.A., and De Oliveira, L.D. (2019) ‘Rosmarinus officinalis L. (rosemary) as therapeutic and prophylactic agent’, Journal of Biomedical Science, 26(5), published online. doi:10.1186/s12929-019-0499-8.