Study Title and Description
Night-time thoughts in high and low worriers: reaction to caffeine-induced sleeplessness.
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||Night-time thoughts in high and low worriers: reaction to caffeine-induced sleeplessness.|
|Author||S Omvik,S Pallesen,B Bjorvatn,J Thayer,IH Nordhus,|
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)?||Therefore, a study was conducted investigating the causal relationship between sleeplessness and nocturnal worry. A 2_x0002_2 (Worry_x0002_Induced sleeplessness) analysis of covariance design was used. The first factor consisted of a subject variable defined by scoring either high or low on a trait measure of worry (the Penn State Worry Questionnaire) and the second factor consisted of 300mg caffeine or placebo|
|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)||Subjects Initially a total of 116 female students at the University of Bergen were recruited. Twenty were excluded due to equipment failure, missing data, or dropout. Ninety-six subjects completed the study (mean age = 21.2, SD = 4.1). Eleven of the participants in the study had incomplete data sets. However, they were included in those analyses where they had complete data. The subjects reported to drink on average one cup of coffee on a daily basis (M = 1.0, SD = 1.4). There were no differences between the high-worry and the low-worry group on caffeine consumption (t(94) = 0.60, p = 0.548). The mean weight of the sample was 64.7 kg (SD = 9.5). Design A 2_x0002_2 analysis of covariance (ANCOVA) design was employed (Worry_x0002_Induced sleeplessness). Worry had the characteristic of a subject variable and the two levels were defined as low-worry and high-worry. The other independent variable, Induced sleeplessness, had its two levels defined as caffeine and placebo. The dependent variables comprised measures of objective and subjective sleep parameters and frequency of nighttime worry. Frequency was selected over other possible dimensions, such as severity or intrusiveness of worrying, based on the finding that it sufficiently predicts pathological worrying (Ruscio et al., 2001). The dependent variables were measured both prior to and following the experimental manipulation. Apparatus and materials Penn State Worry Questionnaire The Penn State Worry Questionnaire is a 16-item self-report measure of trait worry. Each item is rated on a 5-point scale where 1 = ‘‘not at all typical of me’’ and 5 = ‘‘very typical of me’’, thus the total range of scores is between 16 and 80 where an increasing score reflects an increasing amount of reported worry. An example of an item would be: ‘‘When I am under pressure, I worry a lot’’. The Penn State Worry Questionnaire has shown sound psychometric properties with Cronbach alpha coefficients reported in the range from 0.91 to 0.95 (Meyer, Miller, Metzger, & Borkovec, 1990). In the present sample, the Cronbach alpha coefficient was 0.71. Sleep diary A sleep diary was used as a subjective measure of sleep deriving the following parameters: SOL, wake time after sleep onset (WASO), total sleep time (TST) and sleep efficiency (SE), as defined by the formula: ([TST/ total time in bed]_x0002_100). Actigraphy Actigraphy was used as an objective measure of sleep. An Actiwatch Plus unit (Cambridge Neurotechnology, 1999) is worn like a watch on the wrist, and it stores data about time and body movements. These data are later analysed and scored according to specific algorithms in order to be converted into sleep parameters. Actigraphy has been validated against polysomnography (Hauri & Wisbey, 1992) and sleep diary measures (Usui et al., 1999). Night-Time Thoughts Questionnaire The Night-Time Thoughts Questionnaire was used to register nightly worries. The questionnaire comprises 20 items measuring the content of night-time thoughts. Subjects are asked to rate how much they have thought about different topics during the night on a 5-point scale, where 1 = ‘‘not at all’’ and 5 = ‘‘a lot’’, and an increasing score reflects an increasing level of night-time thinking. A sample item from the questionnaire would be: ‘‘Worries about family’’. The questionnaire has six subscales: Mental activity and rehearsal, Thoughts about sleep, Family and long-term concerns, Positive concerns and plans, Somatic pre-occupations, and Work and recent concerns (Watts et al., 1994). Procedures Recruitment took place at lectures held in undergraduate courses at the University of Bergen. All the students, both males and females, were instructed to complete the Penn State Worry Questionnaire and to calculate their own sum scores. The sum scores were controlled by the researcher afterwards. Only female students who scored below or above a given cut-off value on the Penn State Worry Questionnaire were invited to participate in the study. The upper cut-off score (55) and the lower cut-off score (42) were set at approximately a half standard deviation above and below the mean score of the Penn State Worry Questionnaire (M = 48.3, SD = 12.5) according to the Norwegian norms for female students (Pallesen, Nordhus, Carlstedt, Thayer, & Johnsen, 2006). The cut-offs were set at a moderate level to secure a difference between the two groups of one standard deviation. The rationale for recruiting females only was to secure equivalent groups since the Norwegian norms for the Penn State Worry Questionnaire have been found to differ significantly between female and male students in a Norwegian sample (Pallesen, et al., 2006). The resulting two groups consisted of subjects who scored 55 or higher on the Penn State Worry Questionnaire, the high-worry group, and subjects who scored 42 or lower, the low-worry group. The high-worry group had a mean score of 62.0 (SD ¼ 5.3, range ¼ 55–79) and the low-worry group had a mean score of 34.4 (SD = 5.6, range = 19–42). The mean difference between the groups was significant (t(94) ¼ _x0003_24.9, p<0.001). Subjects who were pregnant or breastfeeding, or who reported that they were suffering from a heart or abdominal disease, were excluded from the experiment. The students who fulfilled the inclusion criteria were given an oral explanation of the procedures involved, hereunder answering the Night-Time Thoughts Questionnaire on two consecutive mornings, completing a sleep diary about how their sleep had been on these two nights, wearing an actigraph for the two nights, and taking three pills one hour before bedtime on the second night. They were informed that the pills would contain either 300 mg caffeine or placebo, and that they might experience a poor night’s sleep and/or some side-effects after taking the pills, e.g. headache or nausea. The ratio between the caffeine intake and the subjects mean weight (300 mg/64.7 kg) was 4.6 mg/kg. This represents a strong dose of caffeine (Schapkin, 2000). The subjects were told not to drink any alcohol on the two nights the experiment lasted, and not to complete the experiment during a weekend unless they had the same sleep schedule on the weekend as during the rest of the week. They were also told to go to bed as planned after taking the pills and to press a button on the actigraph when entering the bed at night and when leaving it in the morning so that these times could be registered objectively. Furthermore, they were informed that the experiment was designed to explore how different people react to a poor night’s sleep, and that they would receive 150 NOK as a compensation for participating. Students who agreed to participate were asked to read and sign an informed consent. Eventually, the participants were delivered all the material they needed in an envelope including a written instruction of the procedures, and they were asked to complete the experiment during the following week. The subjects were randomized into a placebo or a caffeine group by a double-blind procedure. Compliance to taking the pills was controlled for when the participants handed in the questionnaires after participation. Statistics SPSS for Windows (Version 13.0) was used in all the statistical analyses. Independent samples t-tests were used to investigate whether the groups differed on various subject characteristics and outcome variables. Independent samples t-tests were also used to investigate whether sub-groups of the sample differed on the discrepancy between subjective and objective sleep measures. A one-way multivariate analysis of covariance (MANCOVA) was used to investigate whether the manipulation was effective in inducing sleeplessness. ANCOVA, using baseline measures as covariates, were run for all the outcome measures to investigate the effects of the manipulation on the repeated measures.|
|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||sleep includes measures of efficiency, latency, duration; Worry was measured by the nighttime thoughts questionnaire and may have been driven by the sleeplessness induced by caffeine|
|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||Actigraphy and sleep diaries were used to measure sleep; Night-Time Thoughts Questionnaire used to measure nighttime worry|
|Caffeine (general)||Caffeine (general)|
|What was the reference, comparison, or control group(s)? (e.g. high vs low consumption, number of cups, etc.)||placebo (no caffeine) vs 300 mg caffeine|
|What were the listed confounders or modifying factors as stated by the authors? (e.g. multi-variable components of models. Copy from methods)||Subjects were not screened for sleep problems before entering the study, so it cannot be ruled out that some of the participants in the study suffered from insomnia or other sleep problems. However, since the study had a repeated measure design, potential individual differences in sleep were controlled for.|
|Provide a general description of results (as reported by the authors).||Statistically significant effects of Induced sleeplessness were found on both the actigraphic variables (F(3,79) = 5.41, p<0.01) and on the sleep diary variables (F(3,87) = 10.95, p<0.001) indicating that caffeine, as compared to placebo, led to increased difficulties initiating and maintaining sleep. SOL increased according to the sleep diary, while WASO increased according to the actigraph. TST decreased both according to the sleep diary and the actigraph. The magnitude of the increase on the various variables can be expressed as effect sizes, such as Cohen’s d. For the sleep diary parameters Cohen’s d was 1.1 for SOL, 0.5 for WASO, 0.9 for TST, and for the atigraphic parameters, Cohen’s d was 0.1 for SOL, 0.5 for WASO, and 0.6 for TST. Significant effects were observed on the sum score of the Night-Time Thoughts Questionnaire and on four of its subscales, respectively on Mental activity and rehearsal, Thoughts about sleep, Positive concerns and plans, and Somatic pre-occupations (See Tables 2 and 3). This means that subjects who received caffeine, as opposed to placebo, thought more about these matters during the experimental night.|
|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?||The results confirmed previous findings that caffeine impairs sleep (e.g. Bonnet & Arand, 1992; Bonnet et al., 2005). The magnitude of the effects, as measured by Cohen’s d, were moderate to high for all but one (SOL according to the actigraph) of the sleep parameters. On these grounds, it could be concluded that that the manipulation had a significant adverse impact on the sleep of the participants. Induced sleeplessness caused an overall increase in the frequency of night-time thoughts, though the finding did not apply to all the subscales of the Night-Time Thoughts Questionnaire. The subscales that did increase were Mental activity and rehearsal, Thoughts about sleep, Positive concerns and plans, and Somatic preoccupations. Taken together, the findings give tentative support to the hypothesis that nocturnal cognitive activity occurs as an epiphenomenon of sleeplessness. Caffeine was effective in inducing sleeplessness. The amount of night-time thoughts increased as a consequence of the manipulation. This finding supports the assumption that nocturnal cognitive activity may represent an epiphenomenon of wakefulness. The effect may be caused by the caffeine itself, by the sleeplessness that was caused by the caffeine, or by an interaction of the two. Taken together, the findings indicate that people with excessive worry may respond more adversely to sleeplessness. Finally, the data give some support to the notion that worry may contribute to overestimation of poor sleep quality.|
|What were the sources of funding?||The study was supported by the Norwegian Research Council.|
|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.||sleep - LOAEL = 300 mg/day (total sleep time, latency to fall asleep) worry - LOAEL = 300 mg/day|
|Notes regarding selection/listing of endpoints and exposures/doses to be compared to Nawrot.||single dose sleep includes adverse effects on both subjective and objective measures (total sleep time, latency to fall asleep)|
|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.