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Acute Low and Moderate Doses of a Caffeine-Free Polyphenol-Rich Coffeeberry Extract Improve Feelings of Alertness and Fatigue Resulting from the Performance of Fatiguing Cognitive Tasks

  • Rachelle A. Reed
  • Ellen Siobhan Mitchell
  • Caroline Saunders
  • Patrick J. O’Connor
Original Research

Abstract

Claims that ingested nutrients can enhance cognitive performance are common but rarely tested. Here, the influence of acute consumption of a polyphenol-rich, non-caffeinated coffeeberry extract on performance of a series of fatiguing cognitive tasks, motivation to do the cognitive tasks, and mood state responses were tested in 30 healthy adults using a block-randomized, double-blind, placebo-controlled, cross-over design. The effects of 300 and 100 mg coffeeberry extracts were compared to beverages without the extract (placebo) and with 75 mg caffeine (positive control). Outcomes were measured before and twice after beverage consumption. Significant self-reported mood effects were found for the positive control indicating sample responsiveness. The coffeeberry extract beverages had non-significant effects on the cognitive test battery performance and motivation to complete these cognitive tasks. The ingestion of the 300 mg and 100 mg coffeeberry extract beverages significantly attenuated perceptions of increased fatigue and decreased alertness resulting from the completion of the fatiguing cognitive tasks. The magnitude of these mental energizing effects was similar for the low and moderate dose extract beverages; thus, there was not support for a dose-response effect. It was concluded that beverages containing low (100 mg) and moderate (300 mg) amounts of a polyphenol-rich, non-caffeinated coffeeberry extract significantly attenuate both increases in self-reported fatigue and decreases in self-reported alertness resulting from the completion of a series of fatiguing cognitive tasks.

Keywords

Cognition Mental energy Mental fatigue Polyphenols 

Introduction

Ingested phenolic compounds, or their metabolites, have acute physiological effects that plausibly could influence human brain function. These effects include attenuating glucose absorption from the small intestine (Manzano and Williamson 2010; Bassoli et al. 2008), enhancing regional brain blood flow, perhaps through actions on nitric oxide (de Mejia and Ramirez-Mares 2014), or binding to adenosine (Karton et al. 1996), GABAA (Wasowski and Marder 2012), nicotinic (Lee et al. 2011), and opioid receptors (Katavic et al. 2007) or receptor tyrosine kinases (Figueira et al. 2017).

The fruit of coffee plants, also referred to as either coffeeberry or coffeecherry and within which resides the coffee bean, contains multiple phenolic constituents (Esquivel and Jimenez, 2011). The most prominent phenols in coffeeberry are chlorogenic acids and the dominant chlorogenic acid is 5-0-caffeoylquinic acid (Mullen et al. 2011; Tajik et al. 2017). Approximately one-third of coffee chlorogenic acids become bioavailable in plasma, after which they can cross the blood-brain barrier and act on the central nervous system (Kim et al. 2012).

Investigations examining the short-term psychological effects of coffeeberry consumption have not been published. However, two studies have documented the acute cognitive and mood effects of ingesting beverages with pure or supplemental chlorogenic acids (Cropley et al. 2012; Camfield et al. 2013).

In the first study of chlorogenic acids, 39 older adults, who habitually drank 1–8 cups of coffee per week, volunteered for a study that involved four treatments consumed on separate occasions across multiple weeks (Cropley et al. 2012). The participants completed a battery of cognitive and mood tests before and 40 min after consuming either a placebo, caffeinated coffee (containing 167 mg caffeine and 244 mg chlorogenic acids), typical decaffeinated coffee (containing 5 mg caffeine and 224 mg chlorogenic acids), or a decaffeinated green coffee blend (NESCAFÉ) which contained a high level of chlorogenic acids (11 mg caffeine and 521 mg chlorogenic acids). Compared to typical decaffeinated coffee, the decaffeinated green coffee blend resulted in significantly attenuated increases in feelings of fatigue that stemmed from the cognitive testing session (d = 0.31) and greater feelings of alertness (d = 0.44). The experimental manipulation, primarily of the level of chlorogenic acids, had no effect on cognitive outcomes. The small (6 mg) difference in caffeine between the conditions is unlikely to have caused the differences in alertness and fatigue but its potential effects cannot be completely ruled out.

A second study of the cognitive and mood effects of chlorogenic acids was conducted by the same research group (Camfield et al. 2013). The investigation was conducted with 58 older adults who were low-to-moderate consumers of caffeine. Comparisons of the acute effects of ingesting 530 mg of pure chlorogenic acids were made to effects that resulted from drinking the decaffeinated green coffee blend with a high level of chlorogenic acids (532 mg + 5 mg caffeine) used in the first study. The alertness and fatigue benefits found after drinking the decaffeinated green coffee blend in the first study were replicated in this follow-up study. Compared to placebo, similar improvements in feelings of fatigue were observed with both treatments. This suggested that beverages with an adequate level of chlorogenic acids improve mental fatigue. Beneficial effects for alertness were found after drinking the decaffeinated green coffee blend beverage but not the drink with pure chlorogenic acids, suggesting that another coffee-related ingredient in the decaffeinated beverage was likely responsible for the favorable alertness outcome. It was suggested that compounds produced in the process of roasting green coffee beans may have accounted for the alertness effect. Quinides produced during roasting, for example, can both bind to serum albumin and influence blood glucose levels (Sinisi et al. 2015; Tunnicliffe and Shearer 2008).

Two unpublished studies, conducted by a single research group (Kennedy et al. 2015; Kennedy and Haskell 2016), have examined the acute cognitive and mood effects of ingesting beverages that contained coffeeberries (extract®, VDF FutureCeuticals (2016)). The first study involved 32 healthy young adults (81% female, 84% Caucasian, mean ± SD age of 22 ± 4 years) who consumed a beverage containing a high dose (1.1 g) of coffeeberry extract standardized to contain 40% coffee polyphenols and combined with beetroot, ginseng, and sage extracts (Kennedy et al. 2015). Compared to a placebo, cognitive function was not significantly changed but the treatment beverage was associated with improved feelings of alertness, vigor, confusion, and mental fatigue.

The second study involved 46 healthy young adults (65% female, 80% Caucasian, mean ± SD age of 23 ± 6 years) (Kennedy and Haskell 2016). Comparisons were made among three beverage treatments: one with the same high dose of coffeeberry (1.1 g) used in the first study and no other added extracts or ingredients except a base containing water, sucralose, preservatives, and flavoring; a second beverage with the same base and coffeeberry dose plus 275 mg of an apple extract; and a third beverage with the same base, a low dose of coffeeberry (100 mg), and the apple extract. The high dose of coffeeberry alone improved feelings of alertness, vigor, fatigue, and increased accuracy on a test of rapid visual information processing at the expense of producing more false alarms but these effects were not replicated with the beverage in which apple extract was added to the high dose of coffeeberry, perhaps resulting from too high a dose of polyphenols (Scholey et al. 2010). The low-dose coffeeberry plus apple extract beverage did not result in large cognitive or mood effects.

The general purpose of the investigation summarized here was to extend what is known about the acute psychological effects of coffeeberry consumption. The aim was to determine if either a low (100 mg) or a moderate dose of coffeeberry (300 mg) alone would show short-term mood, motivation, or cognitive effects compared to a placebo (O'Connor 2006a). A treatment containing 75 mg caffeine was used as a positive control to document participants’ responsiveness to an established psychostimulant. The choice of 75 mg caffeine was based on published research. One review of the literature on the psychological effects of caffeine found most studies show better cognitive performance, indicated by faster reaction times to visual stimuli, after consuming caffeine in doses equal to and above 75 mg while a different review concluded there is an absence of strong evidence for dose-dependent effects of caffeine on cognitive performance (Einother and Giesbrecht 2013; EFSA-Panel 2014). Based on the research briefly summarized above, it was hypothesized that the 300 mg coffeeberry treatment would show beneficial effects on mental fatigue and alertness but have little effect on objectively measured cognitive performance or self-reported motivation to perform the cognitive tests.

Study Participants and Methods

Study Design

The experiment used a block-randomized, double-blind, placebo-controlled, cross-over design. Enrolled participants completed a series of four testing visits and consumed one of four beverages (labeled A, B, C, and D on the bottles) during each session. Specifically, participants were block-randomized to consume beverages in one of eight possible orders (ABCD, ADCB, BADC, BDCA, CADB, CBAD, DABC, or DCBA) using researchrandomizer.org. The beverages were manufactured in two large batches (PepsiCo, Valhalla, NY), poured into 10-oz plastic bottles, labeled with the appropriate randomization code, and shipped overnight to the study site in Athens, Georgia. All beverages were stored in a refrigerator at ~ 3–4 °C until consumed, and all beverages were consumed within 12 weeks of the manufacturing date.

All four beverage conditions contained a base liquid of water, sucralose, acesulfame potassium, preservatives, colors, and flavors. The placebo beverage, labeled treatment A, contained no added caffeine or coffeeberry extract. The positive control beverage, labeled treatment B, contained 75 mg of added caffeine and no extract. The remaining two beverages contained added coffeeberry extract in the amounts of 100 mg (treatment C) and 300 mg (treatment D), respectively, and no caffeine. The specific coffeeberry extract used in the present investigation, referred to as CFE2 (Mullen et al. 2011), contains approximately 51.0% chlorogenic acid, 17.0% 5-caffeoylquinic acid, 3.8% trigonelline, and 1.6% caffeine.

Participants

The University of Georgia’s Institutional Review Board approved all study protocols and materials. Participants were recruited from the local community via flyers placed on local bulletin boards, e-mails sent to selected campus listservs, recruitment announcements in college classrooms, and word of mouth. Participants were compensated at a rate of $15 per hour for study testing visits ($60.00 for each testing session, or $240 for successful study completion).

Sample Size Calculation

A sample size calculation was performed assuming a doubly repeated measures ANOVA design with four beverage treatments and three assessment times in which the measures were expected to be correlated at r = 0.50 across time, and alpha error was set to 0.05. Only beverage × time interactions effects were of interest. A sample size of 30 provided statistical power of 0.85 to detect a significant interaction with a change of 0.5 standard deviations (SD). An effect size of 0.75 SD was expected after consuming 75 mg caffeine while and effect of 0.50 SD was hypothesized after 300 mg coffeeberry based on alertness and mental fatigue responses to caffeine (Maridakis et al. 2009) and coffeeberry (Kennedy et al. 2015; Kennedy and Haskell 2016).

Inclusion/Exclusion Screening Criteria

Male and female adults were eligible for inclusion if they were between ages 18 and 49 years and self-reported good health. Exclusion criteria included self-report of (a) any prescription medication, including birth control; (b) hypersensitivity to caffeine; (c) visual impairment that could not be corrected with glasses or contact lenses; (d) excessive leisure time physical activity (> 7 strenuous bouts weekly); (e) the presence of current gastrointestinal, sleep, or psychiatric disorder; (f) current or recent pregnancy/lactation; (g) smoking or tobacco use; (h) failure to demonstrate adequate minimal performance on computer-based cognitive outcomes during study screening; and (i) participation in another clinical trial within the past 30 days. Inclusion/exclusion criteria were assessed first using online questions and then an in-person screening session was completed.

Online Screening

In response to recruitment efforts, interested persons gave online informed consent and completed screening questionnaires to determine initial eligibility. Questions regarding contact information, age, health status (e.g., medication use, history of psychological disorders), caffeine consumption, and caffeine sensitivity were presented. In order to calculate an estimate of subjective physical activity levels, the Godin Leisure Time Exercise questionnaire was also administered and scored as recommended (Godin et al. 2015). If deemed eligible to advance in the screening process, persons were scheduled for a 1-h in-person screening visit at the University of Georgia.

In-Person Screening

Eligibility from online screening was confirmed in-person, and eligible participants signed an approved informed consent form prior to additional data collection. Participants then completed both a sleep questionnaire and a practice cognitive testing and mood measure battery. The practice battery not only ensured understanding of the instructions and testing procedures but also was used to exclude those potential participants who were unable or unwilling to perform adequately on the cognitive tests. Finally, height (cm) and weight (kg) were obtained using a stadiometer and manual scale, and body mass index (BMI) was then calculated from height and weight measurements.

Experimental Testing Visits

Table 1 illustrates the structure of experimental testing visits. Upon arriving to the laboratory for testing, participants completed a 24-h history questionnaire. Participants confirmed they followed all pre-visit instructions, specifically (a) to eat a similar meal/snack prior to each visit and avoid fasting; (b) to avoid any after dinner or morning caffeine consumption prior to each visit; (c) to avoid moderate-to-vigorous physical activity prior to testing; and (d) to have a typical night of sleep prior to each visit (no more than + 1.5 h from usual amount of sleep that was reported at screening visit). Participants also completed a previous meal log, outlining everything they ate and drank in their most recent meal or snack. The 24-h history questionnaires and previous meal logs were verbally reviewed with participants for accuracy and completion prior to testing. When a participant did not report sufficient sleep or failed to follow other instructions, the testing visit was rescheduled (n = 2).
Table 1

Structure of testing visits. Total time for each visit was 4–4.5 h. Small variations in completion time stemmed from variations in the time taken to complete mood and motivation assessments and/or beverage consumption time

Time (hours:min)

Task

Test phase

0:00–0:05

Greet participant and 24-Hour History Questionnaire

Pre-testing

0:05–0:07

Word and Picture Presentation

Baseline

0:07–0:09

Serial 3 s Subtraction

Baseline

0:09–0:11

Serial 7 s Subtraction

Baseline

0:11–0:16

RVIP

Baseline

0:16–0:19

Mood and Motivation Assessment

Baseline

0:19–0:21

Serial 3 s Subtraction

Baseline

0:21–0:23

Serial 7 s Subtraction

Baseline

0:23–0:28

RVIP

Baseline

0:28–0:31

Mood and Motivation Assessment

Baseline

0:31–0:33

Serial 3 s Subtraction

Baseline

0:33–0:35

Serial 7 s Subtraction

Baseline

0:35–0:40

RVIP

Baseline

0:40–0:43

Mood and Motivation Assessment

Baseline

0:43–0:45

Serial 3 s Subtraction

Baseline

0:45–0:47

Serial 7 s Subtraction

Baseline

0:47–0:52

RVIP

Baseline

0:52–0:55

Mood and Motivation Assessment

Baseline

0:55–1:05

Consume Test Beverage

Beverage

1:05–2:05

60-min Quiet Rest Break

Quiet rest

2:05–3:00

Post Treatment 1 (same procedure as 0:07–0:55)

Post treatment 1

3:00–3:15

15-min Quiet Rest Break

Quiet rest

3:15–4:10

Post Treatment 2 (same procedure as 0:07–0:55)

Post treatment 2

4:10–4:11

Delayed Word Recall

Post treatment 2

4:11–4:13

Delayed Word Recognition

Post treatment 2

4:13–4:15

Delayed Picture Recognition

Post treatment 2

RVIP Rapid Visual Information Processing

Participants then began testing with a 50- to 55-min baseline testing battery. Following baseline testing, participants were given their assigned experimental beverage and asked to consume it fully within 10 min. This was followed by a 60-min quiet rest phase, to allow sufficient time for the beverages to become bioactive. During this 60-min quiet rest break, participants were given the option to watch a Planet Earth documentary or read; participants completed the same quiet rest activity at each testing visit and were asked to refrain from using cell phones during the break. Participants were also allowed to have a few sips of water and use the restroom if needed during the break. Next, post treatment 1 testing was completed, and this was followed by a 15-min break in which participants walked ~ 30 ft to an adjacent room to sit quietly. Finally, participants completed post treatment 2 testing. All testing sessions were conducted in a sound-dampened, isolated testing chamber while seated, and testing visits lasted for approximately 4–4.5 h each.

Cognitive Demand Battery

All testing, other than the 24-h history questionnaire and previous meal log, was completed using a Dell PC (Dell Optiplex 980) with participants seated in a chair with their eyes approximately 18 in. from a 15-in. computer monitor in the testing chamber. The cognitive demand battery (CDB) was delivered using COMPASS software (Version 4.2.1.1, Northumbria University). COMPASS has been used in numerous nutrition-cognition experiments (Scholey et al. 2010; Wightman et al. 2012; Kennedy and Scholey 2004). The Mental and Physical State Energy and Fatigue scales (O'Connor 2004, 2006b) were added to the CDB as was a measure of the degree of motivation to perform the cognitive tests. These scales and the CDB are explained in more detail below:
  1. a.

    Word Presentation: Participants were shown a total of 15 words (1 word at a time, word appeared in the middle of the screen, 1 s stimulus, 1 s inter-stimulus) and were asked to try their best to commit the words to memory, as they would be asked to recall the words later in the testing visit.

     
  2. b.

    Picture Presentation: Participants were shown a total of 15 pictures (1 picture at a time, picture appeared in the middle of the screen, 3 s stimulus, 1 s inter-stimulus) and were asked to try their best to commit the pictures to memory, as they would be asked to recall the pictures later in the testing visit.

     
  3. c.

    Serial 3 s Subtraction Task: A random number between 800 and 999 was displayed in the center of the computer screen, and participants were instructed to repeatedly subtract by 3 from this number for 2 min. Participants were asked to work as quickly and accurately as possible. If participants provided an error response (e.g., incorrect subtraction) but subsequently provided a correct response in relation to the new number, the later was scored as a correct response. Outcome variables included total number of subtraction attempts, total number of error responses, and total number of correct responses.

     
  4. d.

    Serial 7 s Subtraction Task: This task followed the same protocol as Serial 3 s Subtraction, except that participants were asked to subtract serially by 7 for 2 min.

     
  5. e.

    Rapid Visual Information Processing (RVIP): A series of numbers were displayed individually in the center of the screen in quick succession (at a rate of 100 numbers/min) for a continuous 5-min period, and participants were asked to respond when they saw three odd numbers in a row or three even numbers in a row. Participants responded by hitting the center button on a response pad (Cedrus RB-540, San Pedro, CA). Outcome variables included the percentage of strings correctly identified, the reaction time for responding, and the number of error responses or “false alarms.”

     
  6. f.

    Mental Fatigue, Alertness, and Motivation Visual Analogue Scales (VAS): Computerized single-item VAS were used to assess current feelings of mental fatigue, alertness, and motivation. The mental fatigue and alertness scales were anchored with “not at all” on the left and “extremely” on the right, while the motivation scale was “no motivation at all” to “strongest degree of motivation imaginable.” Scores ranging from 0 to 100 were produced.

     
  7. g.

    Mental and Physical State Energy and Fatigue Scales (EFS-State Scales) (O'Connor 2006b): Participants reported their current subjective feelings of physical energy, physical fatigue, mental energy, and mental fatigue by moving the mouse cursor along a visual analogue scale on the computer screen. Each EFS-State scale dimension was comprised of answers from three items that were presented and then summed to composite scores ranging from 0 to 300 mm. Energy items were (a) “I feel I have no energy” to “strongest feelings of energy ever felt”; (b) “I feel I have no vigor” to “strongest feelings of vigor ever felt”; and (c) “I feel I have no pep” to “strongest feelings of pep ever felt.” Fatigue items were (a) “I feel no fatigue” to “strongest feelings of fatigue ever felt”; (b) “I feel no exhaustion” to “strongest feelings of exhaustion ever felt”; and (c) “I have no feelings of being worn out” to “strongest feelings of being worn out ever felt.”

     
  8. h.

    Bond-Lader Scale: Derived from 16 scales that are anchored on each side by adjectives describing a mood, the Bond-Lader Scale provides three composite scores for Alert, Calm, and Content (Bond and Lader 1974). Participants use a computerized VAS to select the intensity of their current feelings on a scale of 0 (absence of feeling) to 100 (presence of feeling).

     
  9. i.

    Delayed Word Recall: Participants were given 60 s to write down as many of the words shown earlier as they can. The number of words correctly recalled, as well as the number or recall errors, was manually scored.

     
  10. j.

    Delayed Word Recognition: Participants were presented with a total of 30 words, one at a time, in the center of the screen. Fifteen of the words presented were presented at the start of each CDB, and the remaining 15 words were decoys. Participants indicated “yes” or “no” using the response pad as quickly and accurately as possible. Outcome variables included number of correct responses, reaction time for correct responses, number of incorrect responses, and reaction time for incorrect responses.

     
  11. k.

    Delayed Picture Recognition: This task followed the same protocol as Delayed Word Recognition, except that participants were shown 30 pictures (15 original and 15 decoys).

     
  12. l.

    Motivation to Perform Cognitive Tasks: Participants were asked to indicate their level of motivation to complete mental work on a VAS. Responses ranged from “0” indicating “No Motivation” to 100 indicating “Highest Motivation Imaginable.”

     

Final Sample

The enrollment and flow of participants through the trial are illustrated in Fig. 1. One hundred sixty-five individuals responded to recruitment efforts and contacted the laboratory to initiate online screening. Seventy-three successfully completed online screening and were eligible to advance to in-person screening. Of the 73 individuals eligible to complete in-person screening, 55 attended screening visits and gave written informed consent; the remaining 18 were lost to follow-up or declined to continue the screening process. Fifteen participants who completed in-person screening either declined to enroll (n = 4) or performed poorly on the screening CDB (n = 11). Forty participants were enrolled and completed at least one experimental testing visit; however, 10 participants were excluded from final analyses due to incomplete data (n = 8 withdrawal due to lack of time, n = 1 family emergency, n = 1 headache). In summary, 30 healthy volunteers completed the full protocol; Table 1 contains demographic information about the final sample included in analyses.
Fig. 1

Flow of participants through recruitment and experiment completion

Statistical Analyses

CDB data were downloaded directly from the COMPASS software and checked for completeness prior to analysis. All other data, including demographic information and previous meal logs, were hand-entered by trained research staff and quality control checked for accuracy and normality; there was an absence of outliers defined as ≥ 3 standard deviations from the mean. All statistical analyses were performed using SPSS (Version 22, IBM SPSS, Armonk, NY). For each outcome, a series of four beverage conditions × 3 time point and 2 beverage (coffeeberry versus placebo) × 3 time point repeated measures ANOVAs were completed. Adjustments for sphericity, when needed, were made using the Huynh-Feldt epsilon. The magnitude of effects from the ANOVAs is provided as partial eta-squared (n2p). Hypotheses were focused on the presence of statistically significant beverage × time interactions; main effects of beverage and time were of no interest. Significant interactions were followed up by one-way ANOVAs and simple effects tests to determine if changes resulting from the test beverage increased at post-beverage 1 or post-beverage 2 compared to baseline or if the test beverages differed from placebo at a specific time point. Cohen’s d effect sizes were also calculated to help interpret the clinical meaningfulness of the results. Alpha level was set a priori at 0.05.

Results

Participants

Selected participant characteristics are shown in Table 2. Thirty participants were 24.67 + 8.79 years old, 53.3% female, 53.3% white, and overweight on average based on BMI (25.01 + 5.56 kg/m2). Participants self-reported typical daily caffeine consumption of 101.17 + 98.47 mg (range 0–300 mg). As assessed by the Pittsburgh Sleep Quality Instrument, participants self-reported 7.27 + 0.70 h of usual sleep per night. Mean self-reported sleep durations the night before testing did not differ among beverage conditions (p = 0.56): placebo (7.28 + 0.87 h), 75 mg caffeine (7.40 + 0.95 h), 100 mg coffeeberry extract (7.33 + 0.85 h), 300 mg coffeeberry extract (7.44 + 0.87 h). A summary of descriptive nutrition data from the last snack/meal prior to testing is provided in Table 3. Mean self-reported energy intake did not differ significantly across the conditions (p = 0.07): placebo (539.37 + 357.05 kcal), 75 mg caffeine (504.30 + 293.37 kcal), 100 mg coffeeberry extract (424.67 + 256.47 kcal), 300 mg coffeeberry extract (487.43 + 324.52).
Table 2

Participant demographics

Variable

Percent/Mean + SD

Range

Age

24.67 + 8.79

19–47

Gender (%)

 Female

53.3

 Male

46.7

Race (%)

 White

53.3

 Black

23.3

 Asian

23.3

Body mass index category (%)

 Normal weight

66.7

 Overweight

23.3

 Obese

10.0

Weight (kg)

72.62 + 17.53

52.16–141.52

Height (cm)

170.98 + 8.71

156.72–191.77

Body mass index (kg/m2)

25.01 + 5.56

19.00–45.80

Usual sleep (hours/night)a

7.27 + 0.70

6.00–9.00

7-day moderate physical activity (h)b

4.60 + 3.35

0.0–12.0

7-day hard physical activity (h)b

1.75 + 2.92

0.0–12.0

7-day very hard physical activity (h)b

2.08 + 2.35

0.0–11.0

7-day physically inactive (h)b

159.56 + 4.68

148.0–167.0

aFrom Pittsburgh Sleep Quality Index administered during screening

bFrom 7-day physical activity recall questions administered during screening

Table 3

Self-reported snack/meal nutrition data. These data represent self-reported intake of food and beverages at the last snack/meal prior to the testing session

Variable

Placebo

100 mg CB

300 mg CB

75 mg caffeine

Total calories (kcal)

539.37 + 357.05

424.67 + 256.47

487.43 + 234.52

504.30 + 293.37

Calories from fat (%)

30.22 + 14.71

33.21 + 18.00

27.89 + 12.63

28.86 + 14.36

Calories from carb (%)

54.63 + 18.73

49.73 + 22.27

56.02 + 17.36

55.13 + 18.56

Calories from pro (%)

14.91 + 8.06

17.06 + 8.34

16.08 + 8.93

15.80 + 8.67

Vitamin E (mg)

3.10 + 4.12

2.51 + 4.06

2.79 + 4.13

3.55 + 4.37

Vitamin B1 (mg)

0.45 + 0.31

0.42 + 0.33

0.51 + 0.38

0.53 + 0.37

Vitamin B2 (mg)

0.55 + 0.46

0.55 + 0.49

0.60 + 0.41

0.74 + 0.73

Vitamin B3 (mg)

6.16 + 8.3

4.62 + 4.32

6.03 + 5.94

6.03 + 5.07

Vitamin B6 (mg)

0.56 + 0.60

0.39 + 0.42

0.49 + 0.45

0.65 + 0.64

Vitamin B12 (mg)

1.08 + 1.55

1.07 + 1.43

1.03 + 1.07

1.06 + 2.69

Lutein/zeaxanthin (mcg)

938.0 + 3002.45

628.40 + 2334.5

1002.76 + 3014.83

959.97 + 3052.32

Zinc (g)

2.52 + 1.81

2.15 + 1.43

2.23 + 1.63

2.9151 + 3.067

mg milligrams, mcg micrograms

Measurements of Compliance

The treatment beverages were consumed in the laboratory by participants under direct supervision of the research team. Therefore, compliance with beverage consumption during testing visits was 100%. No adverse events were observed by the investigators or reported by the participants that could be attributed to beverage consumption. One participant reported a headache at the start of beverage consumption, before it was fully consumed and before enough time had elapsed for it to have become bioavailable. The participant withdrew (Fig. 1).

Cognition, Motivation, and Mood Outcomes

Descriptive statistics for the mood and motivation outcomes are provided in Table 4. Descriptive statistics for the cognitive outcomes are provided in Table 5.
Table 4

Mean (+ SD) scores for subjective mood and motivation variables across beverage conditions and time, and significance of the interaction from the 4 beverage × 3 time ANOVA

Outcome variable

Beverage condition

Baseline (BL)

Post 1 change from BL

Post 2 change from BL

Beverage × time p value

Mental fatigue (VAS within CDB)

Placebo

46.78 + 20.98

1.83 + 15.84

10.54 + 21.44

0.177

75.0 mg C

44.26 + 20.91

− 4.54 + 15.18

2.18 + 24.80

100 mg CB

41.65 + 19.94

2.28 + 9.21

8.17 + 13.97

300 mg CB

45.55 + 19.83

− 3.74 + 15.76

4.28 + 18.37

Alertness (VAS within CDB)

Placebo

48.83 + 20.26

0.50 + 17.62

− 5.58 + 21.59

0.014

75.0 mg C

50.30 + 21.24

10.56 + 17.12

3.79 + 22.99

100 mg CB

53.35 + 19.43

− 1.20 + 12.65

2.73 + 15.98

300 mg CB

49.15 + 19.91

5.28 + 14.91

− 0.94 + 14.48

Motivation (VAS within CDB)

Placebo

49.97 + 17.43

− 0.09 + 13.88

− 6.81 + 17.91

0.009

75.0 mg C

51.11 + 20.07

6.98 + 14.42

3.09 + 20.36

100 mg CB

52.88 + 18.24

− 1.75 + 10.23

− 4.95 + 13.31

300 mg CB

50.48 + 18.60

4.50 + 14.37

− 0.88 + 12.86

Physical energy (EFS State Scale)

Placebo

139.68 + 57.79

9.20 + 38.26

1.55 + 44.09

0.035

75.0 mg C

149.74 + 55.21

28.81 + 42.39

9.48 + 46.04

100 mg CB

156.86 + 54.53

− 1.14 + 27.70

− 6.07 + 37.33

300 mg CB

146.17 + 51.14

11.80 + 37.80

1.47 + 42.97

Physical fatigue (EFS State Scale)

Placebo

126.87 + 54.44

− 2.02 + 35.76

9.41 + 55.43

0.275

75.0 mg C

117.27 + 52.98

− 17.33 + 42.29

− 6.08 + 49.35

100 mg CB

116.03 + 53.12

3.31 + 23.32

7.72 + 37.79

300 mg CB

119.61 + 44.16

− 12.83 + 37.91

2.28 + 45.36

Mental energy (EFS State Scale)

Placebo

136.48 + 58.94

4.46 + 37.27

− 10.91 + 51.51

0.021

75.0 mg C

139.73 + 58.69

28.19 + 47.71

9.51 + 56.55

100 mg CB

151.37 + 58.25

− 1.67 + 27.70

− 10.03 + 36.93

300 mg CB

138.82 + 55.88

16.13 + 44.47

0.03 + 47.03

Mental fatigue (EFS State Scale)

Placebo

141.84 + 57.24

1.53 + 40.86

19.59 + 57.97

0.033

75.0 mg C

136.03 + 56.63

− 24.70 + 43.31

− 1.33 + 56.79

100 mg CB

128.59 + 58.64

3.74 + 28.72

12.58 + 36.16

300 mg CB

137.32 + 54.25

− 13.86 + 44.94

1.75 + 50.01

Alertness (Bond-Lader)

Placebo

52.04 + 20.36

0.37 + 14.19

− 5.59 + 16.67

0.014

75.0 mg C

55.55 + 19.63

7.88 + 13.84

3.08 + 15.19

100 mg CB

54.89 + 19.39

− 0.22 + 8.35

− 1.24 + 14.54

300 mg CB

53.27 + 19.35

4.18 + 14.50

1.31 + 14.84

Calmness (Bond-Lader)

Placebo

66.88 + 12.49

− 2.83 + 8.62

− 2.93 + 12.44

0.485

75.0 mg C

68.40 + 13.65

0.88 + 38.38

− 4.11 + 11.82

100 mg CB

65.18 + 14.24

− 0.24 + 9.26

0.98 + 13.79

300 mg CB

69.39 + 12.62

− 3.83 + 9.04

− 0.59 + 10.04

Contentedness (Bond-Lader)

Placebo

65.21 + 15.08

− 0.37 + 10.71

− 4.09 + 13.34

0.090

75.0 mg C

65.05 + 15.47

3.71 + 6.41

0.97 + 10.25

100 mg CB

63.66 + 19.63

1.48 + 5.83

0.53 + 11.50

300 mg CB

64.97 + 17.46

2.67 + 10.03

2.26 + 8.49

VAS Visual Analogue Scale, CDB cognitive demand battery, C caffeine, CB coffeeberry extract, BL baseline

Table 5

Mean (+ SD) scores for objective cognitive variables across beverage conditions and time, and the significance of the interaction from the 4 beverage × 3 time ANOVA

Outcome variable

Beverage condition

Baseline (BL)

Post 1 change from BL

Post 2 change from BL

Beverage × time p value

Serial threes (number attempted)

Placebo

54.88 + 23.45

6.57 + 8.62

6.6 + 14.47

0.736

75.0 mg C

56.40 + 20.77

6.68 + 9.66

7.27 + 10.04

100 mg CB

57.37 + 22.53

5.74 + 8.87

8.66 + 10.39

300 mg CB

53.69 + 19.55

5.94 + 9.05

5.30 + 10.28

Serial threes (correct attempts)

Placebo

53.59 + 24.11

5.83 + 8.77

5.54 + 14.87

0.568

75.0 mg C

53.83 + 21.15

7.26 + 11.19

6.90 + 11.58

100 mg CB

55.86 + 23.81

4.65 + 10.01

7.39 + 11.63

300 mg CB

51.63 + 19.91

6.82 + 10.90

4.35 + 11.27

Serial threes (errors)

Placebo

1.94 + 1.36

0.07 + 1.43

− 0.13 + 1.36

0.311

75.0 mg C

2.81 + 3.03

− 0.83 + 2.91

− 0.79 + 3.06

100 mg CB

2.03 + 1.87

0.42 + 1.91

− 0.10 + 1.75

300 mg CB

2.30 + 1.83

0.06 + 1.58

− 0.23 + 1.87

Serial sevens (number attempted)

Placebo

30.933 + 18.33

1.98 + 5.08

4.24 + 5.84

0.253

75.0 mg C

31.52 + 14.88

4.32 + 5.39

5.21 + 6.13

100 mg CB

33.76 + 18.66

3.28 + 5.57

5.10 + 8.08

300 mg CB

31.43 + 15.87

2.31 + 3.82

2.41 + 8.12

Serial sevens (correct attempts)

Placebo

28.52 + 18.95

1.38 + 5.07

4.38 + 6.04

0.138

75.0 mg C

29.05 + 15.03

4.55 + 5.70

5.68 + 6.29

100 mg CB

31.58 + 19.09

3.24 + 6.59

5.21 + 8.62

300 mg CB

29.21 + 16.13

2.53 + 3.98

2.53 + 8.10

Serial sevens (errors)

Placebo

2.52 + 2.27

0.60 + 4.34

− 0.14 + 1.99

0.381

75.0 mg C

2.57 + 1.52

− 0.54 + 1.43

− 0.48 + 1.32

100 mg CB

2.28 + 1.82

0.03 + 1.53

− 0.11 + 1.31

300 mg CB

2.32 + 1.51

− 0.22 + 1.18

− 0.12 + 1.04

RVIP (percent correct)

Placebo

47.06 + 24.35

0.54 + 13.96

0.10 + 13.28

0.226

75.0 mg C

47.54 + 23.19

5.49 + 11.61

5.75 + 12.52

100 mg CB

47.23 + 23.88

6.60 + 12.66

3.27 + 15.03

300 mg CB

46.13 + 22.83

3.67 + 14.20

0.08 + 13.21

RVIP (response time to correct answers)

Placebo

540.40 + 71.78

− 1.57 + 44.79

17.38 + 56.92

0.112

75.0 mg C

557.30 + 54.81

− 18.34 + 39.42

− 14.94 + 37.95

100 mg CB

533.98 + 90.57

14.72 + 76.39

12.58 + 65.77

300 mg CB

551.72 + 69.62

− 2.72 + 48.88

4.90 + 49.78

RVIP (false alarms)

Placebo

5.81 + 7.39

− 0.88 + 5.66

− 1.75 + 6.22

0.394

75.0 mg C

4.81 + 5.22

0.29 + 5.12

− 1.13 + 4.76

100 mg CB

6.12 + 5.49

− 2.94 + 5.19

− 2.79 + 4.47

300 mg CB

6.40 + 7.37

− 2.02 + 5.87

− 2.37 + 5.23

Word Recognition (percent correct)

Placebo

75.89 + 12.34

− 3.44 + 12.87

− 1.78 + 13.01

0.701

75.0 mg C

77.89 + 10.85

− 3.89 + 10.97

− 2.56 + 11.86

100 mg CB

80.33 + 11.32

− 6.44 + 13.59

− 2.77 + 9.87

300 mg CB

76.44 + 11.90

− 1.97 + 9.34

1.11 + 11.42

Word Recognition (overall response time)

Placebo

1247.83 + 339.53

− 90.54 + 408.96

− 193.62 + 362.04

0.116

75.0 mg C

1249.51 + 338.19

− 56.12 + 379.40

− 195.14 + 352.73

100 mg CB

1130.63 + 392.81

− 39.37 + 244.94

− 53.97 + 192.57

300 mg CB

1230.08 + 353.24

− 197.5 + 318.12

− 124.39 + 463.76

Word Recognition (correct response time)

Placebo

1262.93 + 396.46

− 134.93 + 473.0

− 238.33 + 435.14

0.090

75.0 mg C

1209.07 + 318.88

− 58.10 + 392.50

− 189.34 + 339.90

100 mg CB

1083.71 + 391.07

− 7.67 + 287.05

− 30.04 + 186.80

300 mg CB

1159.22 + 317.32

− 162.50 + 264.8

− 74.07 + 406.28

Picture Recognition (percent correct)

Placebo

90.89 + 8.89

− 3.78 + 12.37

− 2.44 + 12.28

0.880

75.0 mg C

91.10 + 9.28

− 5.33 + 10.60

− 2.78 + 9.39

100 mg CB

89.56 + 9.50

− 2.22 + 8.89

− 1.56 + 9.74

300 mg CB

89.44 + 8.26

− 3.33 + 7.63

− 1.66 + 8.57

Picture Recognition (overall reaction time)

Placebo

1057.93 + 251.77

− 62.58 + 226.97

− 104.17 + 246.94

0.712

75.0 mg C

1023.57 + 191.65

− 0.73 + 180.38

− 74.92 + 165.48

100 mg CB

1046.43 + 198.92

− 35.25 + 205.90

− 72.90 + 181.25

300 mg CB

1079.95 + 278.22

− 85.75 + 217.75

− 115.23 + 209.98

Picture Recognition (correct reaction time)

Placebo

1020.75 + 231.65

− 50.28 + 230.10

− 88.41 + 223.79

0.727

75.0 mg C

989.95 + 162.90

− 5.57 + 147.20

− 70.72 + 1239.49

100 mg CB

1014.55 + 184.93

− 47.13 + 200.29

− 56.42 + 192.02

300 mg CB

1044.34 + 263.56

− 80.77 + 202.20

− 104.70 + 209.41

Word Recall (number correct)

Placebo

2.10 + 1.99

− 1.43 + 1.71

− 1.33 + 1.84

0.133

75.0 mg C

2.32 + 2.13

− 1.40 + 2.21

− 1.03 + 7.78

100 mg CB

3.53 + 2.03

− 0.62 + 1.67

0.50 + 1.58

300 mg CB

2.21 + 2.10

− 1.45 + 2.26

− 0.57 + 2.39

Word Recall (number of errors)

Placebo

0.50 + 0.82

0.07 + 0.74

0.20 + 0.85

0.125

75.0 mg C

0.77 + 1.07

0.47 + 1.14

0.40 + 1.16

100 mg CB

0.50 + 1.07

− 0.20 + 1.06

− 0.10 + 0.92

300 mg CB

0.87 + 1.07

0.43 + 0.94

0.27 + 0.98

C caffeine, CB coffeeberry extract, BL baseline

Positive Control Beverage

The beverage with 75 mg caffeine had insignificant effects on the cognitive outcomes. This beverage significantly increased motivation to perform the cognitive tasks as well as feelings of alertness, mental energy, and physical energy, while reducing feelings of mental fatigue (all interaction p values < 0.035). Thus, as expected, the group showed responsiveness to caffeine; however, significant effects of the positive control for the group were restricted to the self-reported mood and motivation outcomes.

Coffeeberry Extract Beverages

Statistical details are provided only for the statistically significant results.

100 mg Coffeeberry Extract

Mental Fatigue (CDB)

Compared to placebo, the 100 mg extract beverage resulted in lower mental fatigue at time 3 (Fig. 2). Mental fatigue scores from the CDB were lower at time 3 for the 100 mg extract beverage (t = 2.227, df = 29, p = 0.034) compared to placebo.
Fig. 2

Mean (± SE) self-reported feelings of mental fatigue at baseline (1) and both post-treatment testing times (2 and 3). Visual analogue scores were presented as part of the cognitive demand battery and can range from 0 (no feelings of mental fatigue) to 100 (strongest feelings of fatigue)

Alertness (CDB)

Alertness scores from CDB were higher at time 3 for the 100 mg extract beverage (t = − 2.142, df = 29, p = 0.041) compared to placebo (Fig. 3).
Fig. 3

Mean (± SE) self-reported feelings of alertness fatigue at baseline (1) and both post-treatment testing times (2 and 3). Visual analogue scores were presented as part of the cognitive demand battery and can range from 0 (no feelings of mental fatigue) to 100 (strongest feelings of fatigue)

Delayed Word Recall Accuracy

Compared to placebo, the 100 mg extract beverage attenuated the reduction in delayed word recall performance and the group results are illustrated in Fig. 4. The interaction for the 2 beverage (100 mg coffeeberry extract vs. placebo) × 3 time ANOVA was significant (F2, 58, n2p = 0.128, p = 0.019). One-way ANOVA post hoc tests show that the interaction stemmed from a significant decrease in recall accuracy after the placebo beverage (F2, 58, n2p = 0.312, p < 0.001) that did not occur after consumption of the 100 mg extract beverage (p = 0.074). There was a significant difference between the two beverages at time 3 (t = − 4.014, p < 0.001) but not time 2 (p = 0.54). The size of the effect at time 3 was moderate (1.38 + 1.89 more words were accurately recalled; Cohen’s d effect size = 0.67 standard deviation).
Fig. 4

Mean (± SE) responses of number of words correctly recalled on the Word Recall task at baseline (1) and twice post-treatment (testing times 2 and 3)

300 mg Coffeeberry Extract

Mental Fatigue (CDB)

At time 3, CDB mental fatigue scores were lower after consuming the 300 mg extract beverage compared to placebo (group means Fig. 2, p = 0.032).

Mental Fatigue (EFS)

For the EFS mental fatigue scores, a 4 × 3 ANOVA showed a significant beverage × time interaction (F6, 174, n2p = 0.75, p = 0.033). The difference in mental fatigue between the placebo condition and 300 mg coffeeberry extract at time 2 was insignificant, but the EFS mental fatigue scores were lower after the 300 mg coffeeberry extract beverage compared to placebo at time 3 was significant (t = 2.755, df = 29, p = 0.01; 139.1 ± 61.2 vs. 161.4 ± 56.8).

Alertness (CDB)

For alertness, a 4 × 3 ANOVA showed a significant beverage × time interaction (Fig. 3; F6, 174, n2p = 0.087, p = 0.014). Feelings of alertness were higher for 300 mg extract than the placebo at time 3 (t = − 3.175, df = 29, p = 0.04; 48.2 ± 21.1 vs. 43.2 ± 19.8).

Contentedness (Bond-Lader)

For contentedness, a 2 beverage (placebo vs. 300 mg coffeeberry) × 3 time ANOVA showed a significant interaction (F1.748, 172.899, n2p = .147, p = 0.013) which was explained in a follow-up one-way ANOVA by insignificant increases in contentedness after consuming 300 mg coffeeberry extract and insignificant decrease in placebo over time. At time 3, contentedness was higher after ingesting the 300 mg extract than placebo (p = 0.03).

Discussion and Conclusion

The primary finding of the present investigation was that the ingestion of beverages containing low (100 mg) and moderate (300 mg) amounts of coffeeberry extract significantly attenuated increases in fatigue and decreases in alertness resulting from the completion of a series of fatiguing cognitive tasks. The magnitude of these mental energizing effects was similar for the low and moderate dose extract beverages; thus, there was not support for a dose-response effect on alertness or fatigue in the range of 100 to 300 mg extract. These findings extend, to low and moderate coffeeberry extract doses, the observation that drinking a beverage with a high amount of coffeeberry extract (1.1 g) can improve reduced feelings of alertness and increased feelings of fatigue that occur in response to sustained performance of fatiguing cognitive tasks (Kennedy and Haskell 2016). The improvements in alertness and mental fatigue could not have resulted from constituents in the vehicle/base (i.e., water, sucralose, preservatives, and flavoring) because these ingredients were included in the placebo drink and the only difference between the placebo and extract drinks was the coffeeberry extract.

The effects of coffeeberry extract on alertness and fatigue became statistically significant 2 to 3 h after beverage consumption; however, inspection of the figures shows that the beverages began to exert mental energizing effects from 1 to 2 h post-ingestion. This information about the time course is potentially useful to researchers interested in examining potential mechanisms for the short-term psychological effects of coffeeberry extract. This study was not designed to directly test a plausible biological mechanism through which coffeeberry extract could influence feelings of alertness and fatigue. However, the psychological effects of coffeeberry extracts observed here 2 to 3 h after consumption were moderately related to the associated changes in alertness and fatigue that resulted from consuming a beverage containing 75 mg of caffeine. These results suggest that some, ~ 16 to ~ 33%, of the variability in alertness and fatigue response to coffeeberry extract can be explained by associated responses to caffeine but most of the variability is independent of how the participants responded to caffeine. This observation indirectly supports the idea that coffeeberry extract produced mental energizing effects that were at least in part independent of CNS adenosine receptors, the mechanism through which caffeine exerts its effects (Kaster et al. 2015; Fredholm 1995), and suggests the possibility that combining coffeeberry extract with caffeine might yield synergistic effects. The present findings also indirectly support that coffeeberry extract may be the key ingredient in improvements in alertness and fatigue resulting from drinking a beverage containing 1.1 g extract combined with beetroot, ginseng, and sage extracts (Cropley et al. 2012; Camfield et al. 2013; Futureceuticals 2016).

Consumption of the coffeeberry extract, in either the low or moderate amount, did not have a significant effect on working memory or sustained attention as assessed from performance on serial three, serial seven, and rapid visual information processing (RVIP) tasks. A larger amount of coffeeberry extract appears to be needed to impact sustained attention given that a beverage containing 1.1 g of coffeeberry extract has been shown to improve RVIP accuracy (Kennedy and Haskell 2016).

Here, the consumption of a beverage containing 100 mg coffeeberry extract attenuated the reduction in delayed word recall performance that occurred over time. This outcome may be a consequence of the alerting effect of the coffeeberry extract on brain circuits involved in memory because arousing stimuli, including energy drinks, can impact delayed memory. If that were the case, however, then delayed word recall performance improvements also should have been found after consumption of the 300 mg coffeeberry extract. A beverage containing 1.1 g of coffeeberry extract also did not improve delayed word recall (Kennedy and Haskell 2016). Given that improvements in delayed word recall were not hypothesized a priori, replication of the delayed word recall performance results is needed to have confidence that the effects were not a chance observation.

Another novel observation of the present study was that the beverage with a moderate amount of coffeeberry extract produced improvements in contentedness scores in response to completing cognitive tests that produced fatigue over time. These results are inconsistent with one prior study of chlorogenic acid which found that there was a trend for lower contentedness after this treatment compared to placebo (Camfield et al. 2013). A meta-analysis of 11 randomized placebo-controlled human studies of acute effects of the tea constituents L-theanine and epigallocatechin gallate found no significant short-term effects on contentedness. As with delayed word recall, the replication of the contentedness results is needed to have confidence that the effects were not a chance observation.

Although the present study was not designed to test hypotheses as to why the subjective responses to the treatments were larger than the objective responses, given the finding a brief discussion is warranted. Prior studies of 100 mg and 200 mg caffeine found similar sensitivity to change for subjective measures of energy and fatigue compared to objective measures of fatigue in response to vigilance tasks (Maridakis et al. 2009). No similar coffeeberry study has been conducted. Multiple factors could account for the larger subjective findings in the present investigation, including variation in unmeasured psychological (e.g., expectations, personality) or biological variables (e.g., sex hormones or poorly understood differences in the action of chlorogenic acid or its major metabolites on cognitive compared to mood neural circuitry) (Temple and Ziegler 2011; Sun et al. 2007; Rebai et al. 2017). Even though the specifics of how chlorogenic acid and its metabolites act on the brain are currently unknown, there is substantial evidence brain circuits that generate affective states such as feelings of energy and fatigue are distinct from the neural circuitry underlying cognitive attentional processes (Lindquist et al. 2012; Fortenbaugh et al. 2017). Thus, a plausible speculation is that the bioactive ingredients from coffeeberry consumption had greater influence on affective compared to the cognitive neural circuitry. This observation may be analogous to the effects sleep deprivation which results in greater negative effects on mood than cognitive performance (Pilcher and Huffcutt 1996).

Limitations

Like all studies, the one summarized here had several limitations. Data from potential confounding variables were self-reported, including food and beverage intake, sleep, exercise, and caffeine intake prior to each testing visit; self-reported data are subject to bias including both recall bias and social desirability bias. Further, no objective measurement of caffeine avoidance, like salivary assessment, was collected in our protocol. Additionally, participants were primarily college-aged and graduate students who were free of chronic health conditions and were not taking prescription medications; thus, our results may not be generalizable to other groups. Lastly, the absence of statistically significant effects of 75 mg caffeine on the cognitive performance measures clouds the ability to interpret the null cognitive findings. Our choice of 75 mg caffeine as the positive control was based on (i) the results of prior studies which indicated that beverages containing caffeine in doses of greater than or equal to 75 mg result in improved performance (reaction time) on cognitive tests and (ii) that reviewers of this literature concluded there is not strong evidence for a dose-response effect. Therefore, we selected a dose likely to produce cognitive effects but less likely to result in adverse effects (e.g., heart palpitations, shakiness). Although the absence of statistically significant effects of 75 mg caffeine on the cognitive tests could be interpreted as a failed study, the general pattern of results suggests otherwise. The results presented in Table 5 show that there was a mean improvement on most of the cognitive outcomes (11 of 17 [65%] cognitive test results) after the consumption of 75 mg caffeine even though the magnitude of these changes were not large enough to achieve statistical significance given the sample size. Experiments investigating treatments with established positive effects also fail to confirm such effects by chance 5% of the time. The inclusion/exclusion criteria may have contributed to responses in the present study that were muted compared to results found in the literature.

Conclusion

It is concluded that beverages containing low (100 mg) and moderate (300 mg) amounts of coffeeberry extract significantly attenuated both increases in self-reported fatigue and decreases in self-reported alertness resulting from the completion of a series of fatiguing cognitive tasks. The coffeeberry extract beverages had no effect on self-reported motivation to complete the cognitive tasks or either working memory or sustained attention performance. Conclusions regarding apparent coffeeberry extract induced improvements in delayed word recall and contentedness should be viewed cautiously because these effects were not hypothesized prior to the start of the study and are less well supported by the extant literature.

Notes

Acknowledgements

The authors thank the participants for their efforts. The hard work of Katie Fritz and Brian Huong is acknowledged for assistance with data collection, entry, and cleaning. The current address for Caroline Saunders is Suntory Beverage & Food Europe LTD, Reading, UK.

Funding Information

The University of Georgia received funding from PepsiCo, Inc. to support this investigation (Contract No. 61660).

Compliance with Ethical Standards

Informed consent was obtained from every participant in the study. The University of Georgia’s Institutional Review Board approved all study protocols and materials.

Conflict of Interest

Drs. Reed and O’Connor have no conflicts of interest. Dr. Saunders has no current conflict of interest but was previously employed as a nutrition scientist at PepsiCo. Dr. Mitchell has a conflict of interest because she is currently senior principal scientist for PepsiCo Global Nutrition R&D.

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© Springer Nature Switzerland AG 2018

Authors and Affiliations

  1. 1.University of GeorgiaAthensUSA
  2. 2.PepsiCo Global Nutrition R&DPurchaseUSA

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