Clinical Cognitive and Cerebral Blood Flow Effects of Greek Mountain Tea
Greek mountain tea (GMT; ironwort; Sideritis scardica, Lamiaceae) aerial parts are a traditional medicine used for respiratory and digestive conditions. Traditional uses of the plant are supported by in vitro studies demonstrating antioxidant, anti-inflammatory, and gastroprotective effects. GMT contains polyphenols (ferulic acid, chlorogenic acid, and apigenin) shown to affect blood flow, neurotransmitter reuptake, and cognition in animal and human studies. Several clinical trials found improvements in cognition and mood when GMT was tested in combination with B vitamins or bacopa (Bacopa monnieri, Plantaginaceae) aerial plant extract. However, no clinical trials have tested the cognitive effects of GMT alone. The purpose of this randomized, double-blind, placebo-controlled trial was to investigate the acute and chronic effects of two doses of GMT on cognition, mood, and cerebral blood flow in healthy older adults.
Healthy adults (n = 155, aged 50-70 years) were enrolled at Northumbria University, Newcastle upon Tyne, the UK from February to August 2017. Included participants were non-smokers and had a body mass index of 18-35 kg/m2. Excluded participants were pregnant or breastfeeding, had a history of substance abuse or psychiatric illness, had a current diagnosis of anxiety, depression, or sleep disorders, were taking medications other than contraceptives or hormone replacements, were taking dietary supplements that would interfere with the study, or had a serious chronic condition. Participants were randomly assigned to one of the four following treatment groups: (1) low-dose GMT extract (475 mg/day), (2) high-dose GMT extract (950 mg/day), (3) active control (240 mg/day ginkgo [Ginkgo biloba, Ginkgoaceae] leaf extract), and (4) placebo. Participants took one capsule at breakfast and one capsule at dinner for 28 days. The GMT extract was a 20% ethanol extract with a total phenolic content of 6.25%. No additional information was provided about the source or processing of GMT or ginkgo extract.
On day one and day 28 of the trial, participants completed a battery of cognitive tests, completed the State-Trait Anxiety Inventory (STAI), and had blood pressure and heart rate measured before and after taking the capsules. A subset of participants (n = 57) underwent near-infrared spectroscopy (NIRS) testing at various time points to measure markers of cerebral blood flow in the prefrontal cortex (total hemoglobin, oxygenated hemoglobin, deoxygenated hemoglobin, and oxygen saturation) before and after taking the capsules.
The authors did not report if there were any significant clinical or demographic differences among the four groups at baseline. Three participants withdrew from the trial due to personal reasons, and one participant in the placebo group withdrew due to illness. The authors discussed only statistically significant results because of the very large number of statistical analyses performed. Mean performance on the picture recognition task was significantly better in the high-dose GMT group compared to the gingko group on day one (P = 0.026) and on day 28 (P = 0.005). The number of false alarms on the Rapid Visual Information Processing test was significantly lower in the high-dose GMT group compared to the placebo group on day 28 (P = 0.017). State anxiety scores on the STAI were significantly lower (improved) from day one to day 28 in the high-dose GMT group compared to the placebo group (P = 0.022) and the ginkgo group (P = 0.028) on day 28. At several time points on day one, both GMT groups had significantly greater oxygen saturation while performing cognitively demanding tasks than the placebo group (all P < 0.05). The low-dose GMT had a greater effect than the high-dose GMT. On day one, the high-dose GMT group had significantly greater total hemoglobin levels at all time points compared to the placebo group (all P < 0.05). The low-dose GMT group had significantly greater total hemoglobin levels at some time points compared to the placebo group (P < 0.05). Both GMT groups had significantly higher oxygenated hemoglobin levels at most time points on day one compared to the placebo group (all P < 0.05). The ginkgo group had significantly lower total hemoglobin levels at all time points and lower oxygenated hemoglobin levels at most time points on day 28 compared to the placebo group (all P < 0.05).
The main finding of this trial was that 950 mg/day GMT significantly reduced anxiety after 28 days. This is consistent with mood-enhancing effects observed for fruit polyphenols and phenolic acids and may be due to inhibition of monoamine oxidase B, an enzyme that breaks down certain neurotransmitters. The high dose of GMT improved performance on two cognitive tasks at the beginning and end of the intervention, suggesting an acute effect of GMT. The cognitive effects of GMT observed on the first day coincide with increased cerebral blood flow. This modulation of cerebral blood flow is consistent with the effects of other plant polyphenols and may be due to nitric oxide-induced vasodilation. The authors note reduced cerebral blood flow and lack of cognitive effects observed for the ginkgo group are not consistent with the literature. The short duration of the intervention or composition of the gingko material may be responsible for the lack of effect. The authors explain the sample size was too small to allow for subgroup analysis based on sex. Future trials should examine sex differences in response to GMT and further explore the optimal dose of GMT, as the lower dose of GMT had some benefits. The authors do not discuss adverse events related to any interventions. It is not clear if safety data were not collected or if they were not reported in the article.
The study was funded by Finzelberg GmbH & Co. KG., Martin Bauer Group. Three authors (Heiner, Feistel, and Suarez) are employees of Finzelberg GmbH & Co. KG. The other authors declare no conflict of interest.
Wightman EL, Jackson PA, Khan J, et al. The acute and chronic cognitive and cerebral blood flow effects of a Sideritis scardica (Greek mountain tea) extract: a double-blind, randomized, placebo-controlled, parallel groups study in healthy humans. Nutrients. July 24, 2018;10(8). doi: 10.3390/nu10080955.