Rosemary (Rosmarinus officinalis) looks lovely in the herb garden, tastes great on chicken, and is an aromatic essential oil used for a variety of conditions, including hair care, dull skin and even aching muscles. According to researchers at the Brain, Performance and Nutrition Research Centre at Northumbria University, U.K., a whiff of the perennial plant may also favorably influence brain performance. 

In a study published in the February issue of Therapeutic Advances in Psychopharmacology, researchers Mark Moss, Ph.D., and Lorraine Oliver, MSc, found that compounds absorbed from rosemary aroma affect cognition and subjective states independently through different neurochemical pathways. To confirm their hypothesis, the researchers designed an experiment to investigate the pharmacology of 1,8-cineole (1,3,3-trimethyl-2-oxabicyclo[2,2,2]octane), one of rosemary’s main chemical components.
 
The investigators tested cognitive performance and mood in a cohort of 20 subjects, who were exposed to varying levels of the rosemary aroma. Four drops of the Tisserand brand pure essential oil were applied to a diffuser pad and placed under the bench inside of each testing cubicle. The “aroma steam” was switched on for five minutes to produce an ambient aroma prior to the introduction of each participant. Participants were randomly assigned to be exposed to the aroma in the cubicle for four, six, eight or 10 minutes prior to complet­ing cognitive tests.
 
None of the participants were told that the scent of rosemary in their cubicle was related to the study; rather they were informed that the study was investigating the relationship between mood and cognitive performance. At the conclusion of the testing, none of the participants indicated that they felt that the aroma had affected them in any way.
 
The subjects performed serial subtraction and visual information processing tasks in a cubicle diffused with the aroma of rosemary. Using blood samples to detect the amount of 1,8-cineole participants had absorbed, the researchers applied pre- and post-testing speed and accuracy tests, as well as mood assessments to judge the rosemary oil’s affects. Venous blood was sampled at the end of the session. Pearson correlations were carried out between serum levels of 1,8-cineole, cognitive performance measures and change in mood scores.
 
According to Dr. Moss and Ms. Oliver, the results indicated “for the first time in human subjects that concentration of 1,8-cineole in the blood is related to an individual’s cognitive performance—with higher concentrations resulting in improved performance.”
 
Specifically, both the speed and accuracy of the performed tasks were improved, which suggested that the relationship is not describing a speed–accuracy trade off. Likewise, the chemical also had an effect on mood, though the effect was less pronounced. However, the researchers explained the mood outcome was “a negative correlation between changes in contentment levels and blood levels of 1,8-cineole,” a fact they found particularly interesting because it suggested that compounds given off by the rosemary essential oil affect subjective state and cognitive performance through different neurochemical pathways. The oil did not appear to improve attention or alertness, however.
 
Terpenes like 1,8-cineole can enter the bloodstream via the nasal or lung mucosa. As small, fat-soluble organic molecules, terpenes are easily able tocross the blood–brain barrier. In addition to rosemary, volatile 1,8-cineole is found in many aromatic plants, including eucalyptus, bay, wormwood and sage, and has already been the subject of several studies, including research that suggests it inhibits acetylcholinesterase (AChE) and butyrylcholinesterase enzymes, which are important in brain and central nervous system neurochemistry—rosemary components may prevent the breakdown of the neurotransmitter acetylcholine.
 
“Only contentedness possessed a significant relationship with 1,8-cineole levels, and interestingly to some of the cognitive performance outcomes, leading to the intriguing proposal that positive mood can improve performance whereas aroused mood cannot,” said Dr. Moss.
 
Typically comprising 35-45% by volume of rosemary essential oil, 1,8-cineole may possess direct pharmacological properties. However, it is also possible that detected blood levels simply serve as a marker for relative levels of other active compounds present in rosemary oil, such as rosmarinic acid and ursolic acid, which are present at much lower concentrations.