Acute and Chronic Effects of Green Oat ( Avena sativa) Extract on Cognitive Function and Mood during a Laboratory Stressor in Healthy Adults: A Randomised, Double-Blind, Placebo-Controlled Study in Healthy Humans

David O Kennedy, Bernd Bonnländer, Stefanie C Lang, Ivo Pischel, Joanne Forster, Julie Khan, Philippa A Jackson, Emma L Wightman, David O Kennedy, Bernd Bonnländer, Stefanie C Lang, Ivo Pischel, Joanne Forster, Julie Khan, Philippa A Jackson, Emma L Wightman

Abstract

Green oat (Avena sativa) extracts contain several groups of potentially psychoactive phytochemicals. Previous research has demonstrated improvements in cognitive function following a single dose of these extracts, but not following chronic supplementation. Additionally, whilst green oat extracts contain phytochemicals that may improve mood or protect against stress, for instance species-specific triterpene saponins, to date this possibility has not been examined. The current study investigated the effects of a single dose and four weeks of administration of a novel, Avena sativa herbal extract (cognitaven®) on cognitive function and mood, and changes in psychological state during a laboratory stressor. The study adopted a dose-ranging, double-blind, randomised, parallel groups design in which 132 healthy males and females (35 to 65 years) received either 430 mg, 860 mg, 1290 mg green oat extract or placebo for 29 days. Assessments of cognitive function, mood and changes in psychological state during a laboratory stressor (Observed Multitasking Stressor) were undertaken pre-dose and at 2 h and 4 h post-dose on the first (Day 1) and last days (Day 29) of supplementation. The results showed that both a single dose of 1290 mg and, to a greater extent, supplementation for four weeks with both 430 mg and 1290 mg green oat extract resulted in significantly improved performance on a computerised version of the Corsi Blocks working memory task and a multitasking task (verbal serial subtractions and computerised tracking) in comparison to placebo. After four weeks, the highest dose also decreased the physiological response to the stressor in terms of electrodermal activity. There were no treatment-related effects on mood. These results confirm the acute cognitive effects of Avena sativa extracts and are the first to demonstrate that chronic supplementation can benefit cognitive function and modulate the physiological response to a stressor.

Keywords: Avena sativa; brain; cognition; green oat extract; phytochemicals; polyphenols; stress; triterpenes; working memory.

Conflict of interest statement

The study was sponsored by Anklam Extrakt GmbH, by whom BB and SCL are employed. However, the sponsors had no input into the data-collection, analysis or interpretation of the results of the study. The authors declare no other conflicts of interest.

Figures

Figure 1
Figure 1
Participant dispositions throughout the trial.
Figure 2
Figure 2
Cognitive and Observed Multitasking Stressor (OMS) assessment. Participants completed a cognitive assessment (Numeric Working memory, Stroop, RVIP, Corsi Blocks) in the general laboratory and then moved to the interview room. They provided a saliva sample (cortisol/α-amylase) and then completed the STAI-state and Bond–Lader mood scales before and after the completion of three four-minute verbal serial subtraction tasks (serial 3 s, 7 s, 17 s, completed in counterbalanced order) and a concomitant computerised tracking task. Heart rate (HR) and galvanic skin response (GSR) were measured throughout performance of the tasks.
Figure 3
Figure 3
Schedule of each testing session (Day 1, Day 29). Participants completed the POMS and GHQ-12, followed by the pre-dose cognitive/OMS assessment. After this, they took their day’s treatment, and then completed further identical cognitive/OMS assessments commencing 2 h and 4 h post-dose. Before departing, they completed the POMS and GHQ-12.
Figure 4
Figure 4
Corsi Blocks working memory task. The effects of treatment from the acute (Day 1) analysis (top panels) and the chronic (Day 29) analysis. Data are estimated means (plus SE) derived from the ANCOVA/LMM analysis, using pretreatment (Day 1 pre-dose assessment) data and participant’s age as covariates. The left-hand panels show the results of planned comparisons between placebo and each dose of green oat extract using data averaged across the day, and the right-hand panels shows planned comparisons during each individual assessment. t, p < 0.1; *, p < 0.05; **, p < 0.01; ***, p < 0.001 in comparison to placebo.
Figure 5
Figure 5
Acute (Day 1) treatment related change in multitasking performance averaged across 2 h and 4 h post-dose assessments. Left panel: subtractions accuracy (errors) and tracking accuracy, Right panel: subtraction speed (total number) and tracking accuracy. Scores for each measure were converted into standardised Z score, with a positive score indicating improved performance in order to analyse data together. Data shown are estimated means (plus SE) derived from the LMM analysis, using pretreatment baseline data and age as covariates. The data for tracking represented in both panels is the same, with differences in the planned comparisons relating to differences in variance across both tasks. t, p < 0.1; *, p < 0.05 in comparison to placebo at that time point.
Figure 6
Figure 6
Chronic (Day 29) treatment related change in multitasking performance averaged across pre-dose, 2 h and 4 h post-dose assessments. Scores for each measure were converted into standardised Z score with a positive score indicating improved performance in order to analyse data together. Data shown are estimated means (plus SE) derived from the LMM analysis, using Day 1 pretreatment baseline data and age as covariates. The Z scores are plotted with an increased score indicating improved performance. The top panels show subtraction accuracy (errors) and tracking accuracy data; the bottom panels show subtraction speed (total number) and tracking accuracy data. In both top and bottom panels the left-hand panels show comparisons of mean Day 29 data averaged across the two concomitantly performed task outcomes (serial subtractions/tracking), and the right-hand panel shows comparisons conducted on the separate task outcomes. The data for tracking is the same in both analyses. t, p < 0.1, *, p < 0.05; ***, p < 0.001 in comparison to placebo.
Figure 7
Figure 7
Chronic (Day 29) treatment related change in multitasking performance (accuracy of subtractions and tracking) during the OMS pre-dose and during the 2 h and 4 h post-dose assessments. Data are estimated means (plus SE) of Z score data, derived from the LMM analysis, using pretreatment (Day 1 pre-dose assessment) data and participant’s age as covariates. The Z scores are plotted with an increased score indicating improved performance. The top panels show subtraction accuracy (errors) the bottom panels show tracking accuracy data from a single LMM analysis. t, p < 0.1, *, p < 0.05; **, p < 0.01; ***, p < 0.001 in comparison to placebo.
Figure 8
Figure 8
Chronic (Day 29) treatment-related change in the electrodermal galvanic skin response to the stressor. Data are change from resting baseline estimated means (plus SE) derived from the LMM analysis, using pretreatment (Day 1 pre-dose assessment) data and age as covariates. The left-hand panel shows planned comparisons between group means averaged across the testing day, and the right panel shows planned comparisons during each individual assessment. *, p < 0.05 in comparison to placebo.

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