Get Involved
About Us
Our Members
Clinical Cognitive and Cerebral Blood Flow Effects of Greek Mountain Tea

Reviewed: 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.

The aerial parts of Greek mountain tea (GMT; Sideritis scardica, Lamiaceae) have been used traditionally to treat respiratory and digestive conditions. These uses are supported by in vitro studies that have demonstrated antioxidant, anti-inflammatory, and gastroprotective effects. GMT contains polyphenols (e.g., ferulic acid, chlorogenic acid, and apigenin) that are reported to affect blood flow, neurotransmitter reuptake, and cognition in animal and human studies. Several clinical trials have reported improvements in cognition and mood when GMT was tested in combination with B vitamins or an extract of bacopa (Bacopa monnieri, Plantaginaceae) aerial parts. However, no clinical trials have investigated the cognitive effects of GMT alone. The purpose of this randomized, double-blind, placebo-controlled trial was to assess the acute and chronic effects of two doses of GMT on cognition, mood, and cerebral blood flow in older adults.

Healthy adults (N = 155, aged 50-70 years) were enrolled at Northumbria University in Newcastle upon Tyne, 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, were taking medications other than contraceptives or hormone replacements, were taking dietary supplements that would interfere with the study, had a serious chronic condition, or had a current diagnosis of anxiety, depression, or a sleep disorder.

Participants were randomly assigned to one of four groups: low-dose GMT extract (475 mg), high-dose GMT extract (950 mg), active control (240 mg ginkgo [Ginkgo biloba, Ginkgoaceae] leaf extract; no additional details provided), or placebo. Participants took one capsule at breakfast and one capsule at dinner every day 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 the GMT or ginkgo extract.

On day one and day 28 of the trial, participants completed a battery of cognitive tests, filled out the State-Trait Anxiety Inventory (STAI) questionnaire, 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 large number of analyses performed.

Mean performance on the picture recognition task was significantly better in the high-dose GMT group compared to the ginkgo group on day one (P = 0.026) and on day 28 (P = 0.005). The number of false alarms (i.e., mistakes) 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). STAI test scores were significantly decreased (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). At several time points on day one, both GMT groups had significantly greater oxygen saturation while performing cognitively demanding tasks than the placebo group (P < 0.05 for all).

On day one, the high-dose GMT group had significantly greater total hemoglobin levels at all time points compared to the placebo group (P < 0.05 for all). 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 (P < 0.05 for all). 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 (P < 0.05 for all).

The main finding of this trial, according to the authors, was that 950 mg GMT extract significantly reduced anxiety after 28 days. The high dose of GMT improved performance on two cognitive tasks at the beginning and end of the intervention, suggesting an acute effect of high-dose 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 effects of other plant polyphenols and may be due to nitric oxide-induced vasodilation.

The authors note that the 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 ginkgo material may be responsible for the lack of effect. The authors explain the sample size was too small to allow for subgroup analyses based on gender. Future trials should examine gender differences in response to GMT and further explore the optimal dose, as the lower dose of GMT also showed some benefits. The authors did not discuss adverse events related to any interventions, and it is not clear if safety data were collected.