Study Title and Description
Naturalistic effects of five days of bedtime caffeine use on sleep, next-day cognitive performance, and mood
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||Naturalistic effects of five days of bedtime caffeine use on sleep, next-day cognitive performance, and mood|
|Author||E. K. Keenan, B. Tiplady, C. M. Priestley and P. J. Rogers|
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 main aim was to assess the effects of bedtime caffeine use on sleep and subsequent daytime performance and mood. A secondary aim was to assess effects of caffeine on sleep over time, that is, tolerance. A further aim was to assess aspects of caffeine use as a model of short-term poor sleep and associated daytime consequences.|
|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)||Nineteen participants (14 women and 5 men aged 32 – 12.9 years) assessed as good sleepers using the statements ‘‘I am satisfied with my sleep’’, ‘‘I feel very tired in the morning’’, ‘‘My sleep is refreshing,’’ and ‘‘I feel very tired during the day’’ from the Bristol Sleep Questionnaire (BSQ)27 were recruited from the Bristol area. Additional criteria included habitual consumption of no more than two cups of caffeinated drink per day, the last one taken at least 4 hours before bedtime. Participants spent 0.47 – 0.57 hours in bed before falling asleep and slept for 7.75 – 1.17 hours and habitually consumed 65 – 53.7 mg/day caffeine (range 0–141 mg/day). Study design and procedure The study was carried out in the field (participants’ normal everyday environment). Participants took part in a randomized, double-blind 2-week counterbalanced crossover study. Caffeine was administered for five nights consecutively for one week and placebo for five nights consecutively the other week, although participants were informed that it was random as to whether they would receive caffeine or placebo on any particular night. Each morning, participants were required to provide a saliva sample, which was not analyzed, but taken to encourage compliance with the study requirements. The weekend acted as a washout when there was no drug administration or testing. Half of the volunteers were instructed to take their caffeine capsule one hour before their usual bedtime, and the other half to take their capsule at lights out. Participants were asked to keep a regular routine throughout the study and to refrain from daytime naps. They were required to complete a Food and Activity Diary before the initial training session to allow discussion of the importance of keeping a regular routine for the duration of the study. Each testing day (Monday–Friday), participants completed tasks assessing mood and cognitive performance (see below) in the morning before showering or eating breakfast and again in the afternoon. They were allowed to continue their usual habitual caffeine intake after they had completed the morning tests to prevent any potential effects of caffeine withdrawal later on.30,31 Drug administration Participants were provided with ten 250mg capsules, five of which contained caffeine BP (caffeine anhydrous powder; Courtin and Warner) and five contained placebo (corn flour). Capsules were a white vegetarian format and were purchased from Capsuline_x0002_ with a disintegration time of < 15 minutes. Sleep analysis Actiwatch Actigraphy Monitors (AW4; Cambridge Neurotechnology) were worn on the nondominant wrist and measured several sleep parameters (sleep efficiency, sleep latency, total activity score, and fragmentation index) by recording the number of changes in state per epoch (30 seconds). Participants were also provided with a sleep diary that contained the items ‘‘difficulty getting to sleep’’, ‘‘quality of sleep’’, ‘‘ease of waking’’, how many times participants woke up restless during the night, and if they were troubled by waking early and not being able to get back to sleep again. Participants also rated how clear-headed/alert/refreshed/ awake they felt upon awakening, how they performed, and how tired and alert they were during the day. Questionnaires The BSQ27 is a 23-item questionnaire that assesses the aspects of quality of sleep, including sleep initiation, maintenance, troubled sleep, and dreams, consequences associated with sleep such as feeling tired the next day and daytime naps, items that can be used to identify possible sleep disorders such as movement disorders, sleep apnea, parasomnias, and possible reasons for poor sleep such as partner’s snoring and young children. The DASS-2129 is a 21-item questionnaire assessing depression, anxiety, and stress, which also provides a total mood score. It has internal consistencies for each factor (Depression [a = 0.91], Anxiety [a = 0.84], Stress [a = 0.90]), which correlate well with other similar measures. Data editing and analysis Determination of the appropriate sample size was difficult due to lack of effect sizes reported in similar previous studies, although three studies most similar to the current one that found significant disruptive effects of caffeine used sample sizes of 6,20 12,16 and 1719 participants. Mood scales presented on the mobile phones were combined, and the resulting components labeled energetic arousal (energetic and alert vs. tired and sleepy) and tense arousal (tense, stressed, miserable, and irritable vs. relaxed) based on Thayer.35 The scale item cheerful was analyzed separately. Three factors were identified using principal component analysis on sleep diary questions: daytime performance and energy, quality of sleep, and awakening. The remaining variables were analyzed separately. Three actiwatches failed to record any data. The questions from the BSQ were grouped into four factors: daytime sleep, troubled sleep (dreams), disturbed sleep, and morning tiredness, based on a factor analysis from a larger study. The scores from the DASS-21 were grouped into three factors (stress, anxiety, and depression) based on previous research from a large nonclinical sample.36 Data were averaged over the week, as reduced performance has also been found after recovery sleep.6 To evaluate differences between caffeine and placebo administration, mixed analyses of variance with within-subject factors of day (1–5) and week (caffeine or placebo) and a between subject factor of order (placebo first or caffeine first) were conducted. The data from the first day only were also analyzed. For analysis of cognitive performance and mood, the time of testing session (morning or afternoon) was also included as a within-subject factor, and the Huynh-Feldt correction was applied when the sphericity assumption was violated. To compare the number of times participants were troubled by waking up early over the week, a McNemar exact test for paired samples using the binomial distribution was used for data at day 1, and t-tests were employed to compare the number of times participants were troubled by waking early over the week.|
|How many outcome-specific endpoints are evaluated?||2|
|What is the (or one of the) endpoint(s) evaluated? (Each endpoint listed separately)||Sleep|
|List additional health endpoints (separately).|
|List additional health endpoints (separately)|
|Notes||Tense was described as 'tense arousal' and consisted of tense, stressed, miserable, and irritable vs. relaxed|
|What is the study design?||Controlled Trial|
|Randomized or Non-Randomized?||RCT|
|What were the diagnostics or methods used to measure the outcome?||Both|
|Optional: Name of Method or short description||sleep diary; questionnaire; actiwatch (activity monitor)|
|Caffeine (general)||Caffeine (general)|
|What was the reference, comparison, or control group(s)? (e.g. high vs low consumption, number of cups, etc.)||counter-balanced cross-over study; subjects either took a 250 mg capsule or a placebo|
|What were the listed confounders or modifying factors as stated by the authors? (e.g. multi-variable components of models. Copy from methods)||none listed|
|Provide a general description of results (as reported by the authors).||Sleep analyses Table 1 shows that after the first night of administration, caffeine resulted in higher total activity and fragmentation index scores, and marginally insignificant lower sleep efficiency scores. There was a trend for subjective quality of sleep to be rated as worse after caffeine (see also Fig. 1), and significantly more participants were troubled by waking early after they had consumed caffeine. Figure 1 shows that caffeine had a particularly striking effect on sleep quality of three participants who subsequently withdrew from the study. Over days 2–5, caffeine administration resulted in significantly lower sleep efficiency scores compared to placebo. There were no other effects of caffeine on days 2–5, including no effect of caffeine on sleep quality (Fig. 1). Mood Cheerfulness was significantly lower over days 2–5 of the caffeine week, but not on the first day (Table 1). [ no comment on tense mood] Effect of habitual caffeine intake Habitual caffeine intake was significantly negatively correlated with fragmentation index scores averaged over days 1–5 that participants were administered caffeine before bedtime r =_x0002_0.658, p = 0.008, n = 13 (with age as covariate), higher restlessness scores being associated with lower habitual caffeine intake (Fig. 3).|
|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?||Although caffeine disrupted sleep objectively and somewhat subjectively in habitually low- and noncaffeine consumers, on the surface, the next-day performance appeared better after bedtime consumption of caffeine as compared to placebo, presumably due to the presence of residual caffeine still present in the morning and beyond. Even though this study was not designed to assess whether effects of caffeine are related to a net benefit or reversal of withdrawal effects, the most plausible explanation here is that bedtime caffeine use was preventing the adverse effects of overnight caffeine withdrawal that would likely have occurred during placebo administration. Furthermore, partial tolerance developed to the effects of caffeine on sleep. Due to this tolerance over repeated testing, withdrawal of participants most affected by caffeine, and residual effects of caffeine the following morning, the use of caffeine in low- and noncaffeine nonsumers in a naturalistic field setting is not recommended for modeling the effects of poor sleep on the next-day performance and mood.|
|What were the sources of funding?||This research was supported jointly by the Biotechnology and Biological Sciences Research Council (student grant reference number BBSRC DTC/PSYC SG1421.6525) and Glaxo-SmithKline.|
|What conflicts of interest were reported?||None|
|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.||Sleep (subjective quality and efficiency) - LOAEL = 250 mg Tense - NOAEL = 250 mg|
|Notes regarding selection/listing of endpoints and exposures/doses to be compared to Nawrot.||single dose Effects on sleep below levels in Nawrot|
|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|
No quality dimensions were specified.
No quality rating data was found.