Study Title and Description
Caffeine can decrease subjective energy depending on the vehicle with which it is consumed and when it is measured.
Key Questions Addressed
|1||For [population], is caffeine intake above [exposure dose], compared to intakes [exposure dose] or less, associated with adverse effects on behavior*?|
Primary Publication Information
|Title||Caffeine can decrease subjective energy depending on the vehicle with which it is consumed and when it is measured.|
|Author||HA Young,D Benton,|
Secondary Publication Information
There are currently no secondary publications defined for this study.
Extraction Form: Behavior - Design Details - INCLUDED Studies
No arms have been defined in this extraction form.
|Question... Follow Up||Answer||Follow-up Answer|
|What outcome is being evaluated in this paper?||Behavior|
|What is the objective of the study (as reported by the authors)?||The objective of this study was to consider the influence on interstitial glucose levels, mood and cognition of drinks differing in their caffeine content and glycaemic load.|
|Provide a general description of the methods as reported by the authors. Information should be extracted based on relevance to the SR (i.e., caffeine related methods)||Ninety minutes after a standard breakfast, a yoghurt-, glucose- or water-based drink, with or without 80 mg of caffeine, was consumed. Three hundred and forty-five undergraduates were recruited when they responded to a circular e-mail and were randomly and blindly allocated to one of the six conditions. There were 175 men and 162 women, with mean age of 21.78 (3.51)years. Subjects were excluded if they were diabetic, suffered from any food allergies/intolerances or if their BMI was outside the healthy range (18.5–25.0). The six experimental groups did not differ in the proportion of each gender, BMI or their average age. The sample was randomly divided into six groups (numbers in parentheses) that mid-morning consumed one of the following 250-ml drinks. 1. Yoghurt-based (GL=3.6) with no caffeine (N=60) 2. Yoghurt-based (GL=3.6) with 80 mg caffeine (N=56) 3. 39 g glucose (GL=30) with no caffeine (N=57) 4. 39 g glucose (GL=30) with 80 mg caffeine (N=61) 5. Flavoured water with no caffeine (N=55) 6. Flavoured water with 80 mg caffeine (N=56) A single serving of the yoghurt-based drink provided 3.25 g fat, 6.25 g protein, 22.5 g available carbohydrate and 5.6 g of soluble fibre. Variants 1–4 contained 155 kcal, and all drinks were orange-flavoured. The water-based drinks were artificially sweetened using sucralose so that they matched the sweetness of the glucose-based drinks. All the drinks were provided in opaque plastic bottles. Subjects were blind as to the nature of the drink that they consumed and were unaware that their drinks may have differed from others. The researcher was blind as to the nature of the drinks. The subjects were given a maximum of 10min to consume the drink, after which they sat quietly reading or watching television. Mood Subjects were asked to report how they feel ‘at this moment’ using visual analogue scales. The pairs of adjectives used at the ends of 100-mm lines reflected the dimensions used in the Profile of Mood States Questionnaire: Composed/Anxious; Hostile/Agreeable; Elated/Depressed; Unsure/Confident; Energetic/Tired; Confused/Clearheaded. In all cases, a higher score reflected a more positive mood. Statistical analysis Data were analysed using appropriate analysis of covariance. The basic approach involved a vehicle (yoghurt, glucose, water)×caffeine (0 or 80 mg)×test session (30, 90 and 150 min) design. Performance in the test session prior to consuming a drink was used as a covariate. Another factor was added where there was more than one level of a variable, for example mood before and after a test session, or with reaction times the responses to the various number of lights.|
|How many outcome-specific endpoints are evaluated?||6|
|What is the (or one of the) endpoint(s) evaluated? (Each endpoint listed separately)||anxious|
|List additional health endpoints (separately).||tired|
|List additional health endpoints (separately)||confused|
|What is the study design?||Controlled Trial|
|Randomized or Non-Randomized?||RCT|
|What were the diagnostics or methods used to measure the outcome?||Subjective|
|Optional: Name of Method or short description||Visual analogue scale based on Profile of Mood states|
|Caffeine (general)||Caffeine (general)|
|What was the reference, comparison, or control group(s)? (e.g. high vs low consumption, number of cups, etc.)||no caffeine vs caffeine (80 mg)|
|What were the listed confounders or modifying factors as stated by the authors? (e.g. multi-variable components of models. Copy from methods)||Statistical analysis Data were analysed using appropriate analysis of covariance. Performance in the test session prior to consuming a drink was used as a covariate. Another factor was added where there was more than one level of a variable, for example mood before and after a test session, or with reaction times the responses to the various number of lights.|
|Provide a general description of results (as reported by the authors).||Energetic/tired The interaction vehicle×caffeine×test session reached statistical significance [F(4,636)=2.65, p<0.03], which reflected a range of differences (Fig. 4). 1. There were no differences in ratings of being energetic 30 min after the consumption of any drink irrespective of the type of vehicle or caffeine consumption. 2. With the water-based drinks, at both 90 min (p<0.008) and 150 min (p<0.002), those receiving caffeine reported being more tired. 3. In those consuming the yoghurt-based drink, the adding of caffeine increased reports of energy at 90 min (p<0.02), and there was a similar trend after 150 min (p<0.06). 4. Adding caffeine to the glucose-based drink did not influence ratings of energy at any stage throughout the morning. 5. In those who received caffeine, a yoghurt- rather than a glucose-based drink resulted in feeling more energetic (p<0.03) at 90 min. In addition, adding caffeine to yoghurt rather than a water-based drink resulted in reports of greater energy at both 90 min (p<0.0001) and 150 min (p<0.0001). At both 90 min (p<0.005) and 150 min (p<0.002), adding caffeine to a glucose rather than water vehicle resulted in feeling more energetic. There was also a vehicle×caffeine×before/after test session interaction [F(2,318)=3.33, p<0.04] that considered the influence of the drink on changes in perceived energy over the duration of the testing sessions (Fig. 5): that is, the extent to which energy was maintained, rather than fatigue induced, by performing the test battery. 1. Adding caffeine to a water-based drink resulted in a greater fall in energy levels over the testing session; that is, subjects felt more tired than when caffeine had not been taken (p<0.02). 2. With the glucose-based drinks, there were no differences between those who did and did not consume caffeine. 3. Adding caffeine to the yoghurt drink resulted in the testing session inducing less tiredness; that is, subjects reported feeling more energetic when tested 90 min after consumption (p<0.02), with a similar trend at 150 min (p<0.06). 4. There were no differences in the response to vehicles in those who did not consume caffeine. 5. When caffeine had been consumed, those who drank glucose became less tired over the testing session than those who consumed water (p<0.03). 6. Similarly, after caffeine consumption, those who drank yoghurt reported feeling less tired after testing than those who had consumed water (p<0.0001). Given the unexpected negative response to caffeine in water-based drinks, the immediate influence of caffeine 30 min post-consumption, before taking any tests, was considered. Ratings of being energetic/tired were examined by subtracting the rating before a drink to ratings 30 min after a drink, but before a test battery was performed. The main effect of caffeine was not significant [F(1,331)=0.01, n.s.]; however, the interaction vehicle×caffeine reached statistical significance [F(2,331)=3.21, p<0.04]. Table 1 reports the interaction, with a positive score indicating feeling more energetic and a negative score feeling more tired. Those who drank caffeine in combination with water reported being significantly more energetic than those who drank caffeine with glucose (p<0.03) or yoghurt (p<0.03). There were no differences between the glucose and yoghurt conditions when caffeine was taken. There were also no significant differences between the three drinks in those consuming no caffeine [F(2,165)=0.52, n.s.]. In summary, there was a short-term benefit of consuming caffeine when it was taken with water. Elated/depressed Ratings of feeling elated rather than depressed were not influenced by the nature of the drink. Vehicle [F(2,315)= 0.64, n.s], whether caffeine was consumed [F(1,315)=1.03, n.s] and the interaction between these factors did not achieve statistical significance [F(2,315)=0.95, n.s]. Anxious/composed Similarly, when ratings of being composed/anxious were examined, the vehicle [F(2,316)=1.15, n.s.] and caffeine main effects [F(1,316)=1.19, n.s.] were not significant, and neither was the interaction between these factors [F(2,316)=2.20, n.s.]. Confident/unsure With ratings of being confident/unsure, there was a four-way interaction [F(4,632)=2.51, p<0.04], but as these higher-order interactions appeared to reflect a chance difference in one cell, it was not further considered. Agreeable/hostile With ratings of being agreeable/hostile, the interaction vehicle×caffeine×test session reached statistical significance [F(4,640)=4.07, p<0.003], although post hoc tests failed to find any statistically significant differences between conditions. There was also a vehicle×caffeine×before/after test session interaction [F(2,321)=7.32, p<0.02]. When changes in ratings over the testing sessions were considered, when no caffeine was included, the nature of the vehicle did not influence the findings. However, when caffeine was added to yoghurt, subjects reported being statistically more agreeable when finishing the test session [+6.69 (3.42)] than if a water and caffeine had been drunk [−5.96 (3.21), p<0.008]. Similarly, caffeine added to glucose had a more positive influence [+4.86 (3.29), p<0.02] than with the water and caffeine combination. With both yoghurt and glucose, adding caffeine did not alter the response to the testing sessions. However, water by itself [+7.87 (4.38)] differed from water plus caffeine [−5.96 (3.21), p<0.007]; that is, caffeine increased reports of hostility. Clearheaded/confused With reports of feeling clearheaded/confused, the interaction vehicle×caffeine×test session reached statistical significance [F(4,578)=3.47, p<0.007], although post hoc tests failed to find statistically significant differences.There was also vehicle×caffeine×before/after test session interaction [F(2,317)=3.17, p<0.04] that reflected a negative reaction to caffeine in water-based drinks. When changes in ratings over the testing sessions were considered, the water-based drink without caffeine resulted in higher levels of clearheadedness [+9.80 (4.77)], whereas adding caffeine to water resulted in reports of increased confusion [−4.76 (4.27), p<0.02].|
|Did the authors perform a dose-response analysis (or trend/related analysis)?||No|
|What were the authors's observations re: trend analysis?|
|What were the author's conclusions?||Caffeine as such produced no consistent change in mood over the morning; rather, the response depended on the vehicle to which it was added and the time when it was assessed (Figs. 4 and 5). Those who consumed a caffeine- rather than a non-caffeine-containing waterbased drink reported in the later morning being more tired, hostile and confused. In contrast, adding caffeine to a yoghurt-based drink resulted in reports of being more energetic, agreeable and clearheaded. Consistently, those who had taken caffeine were in a better mood when it was associated with yoghurt- rather than water-based drinks, whereas without caffeine the nature of the vehicle was unimportant. Such findings contrast with the received wisdom that in "low to moderate doses, caffeine has been quite consistently shown to increase positive affect" (Smith et al. 2004). The present short-term positive response to caffeine (Table 1) is consistent with this summary. These comments, however, reflect almost entirely studies of the short-term response to consumption rather than the effect after 2–3 h. It appears that rather than making generalizations about caffeine, comments need to be placed in the context of the diet and the timescale of its action. As expected, caffeine, when taken with water, when compared with water alone, increased reported energy after 30 min. However, when caffeine was combined with glucose, no such benefit was observed, suggesting that in this respect the consumption of glucose antagonised the effect of caffeine.|
|What were the sources of funding?||None listed|
|What conflicts of interest were reported?||N/A|
|Does the exposure (dose) need to be standardized to the SR?||No|
|Provide calculations/conversions for the exposure based on the decision tree in the guide (for all endpoints/exposure levels of interest).|
|List all the endpoint(s) followed by the dose (mg) which will be used in comparison to Nawrot. Characterize value as LOAEL/NOAEL, etc. if possible.||Caffeine in Water: Tired - LOAEL = 80 mg Depressed - NOAEL = 80 mg Anxious - NOAEL = 80 mg Unsure - NOAEL = 80 mg Hostile - LOAEL = 80 mg Confused - LOAEL = 80 mg Caffeine in yogurt: Tired - NOAEL = 80 mg Depressed - NOAEL = 80 mg Anxious - NOAEL = 80 mg Unsure - NOAEL = 80 mg Hostile - NOAEL = 80 mg Confused - NOAEL = 80 mg Caffeine plus sugar: Tired - NOAEL = 80 mg Depressed - NOAEL = 80 mg Anxious - NOAEL = 80 mg Unsure - NOAEL = 80 mg Hostile - NOAEL = 80 mg Confused - NOAEL = 80 mg|
|Notes regarding selection/listing of endpoints and exposures/doses to be compared to Nawrot.||single dose Caffeine in yogurt actually improved ratings of tiredness|
|What is the importance of the study with respect to the adverseness of the outcome?||Important|
No baseline characteristics have been defined for this extraction form.
Results & Comparisons
No Results found.
|Arm or Total||Title||Description||Comments|
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No quality rating data was found.