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Study Title and Description

Sleep duration and caffeine consumption in a French middle-aged working population.



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*?
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Primary Publication Information
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TitleData
Title Sleep duration and caffeine consumption in a French middle-aged working population.
Author M Sanchez-Ortuno,N Moore,J Taillard,C Valtat,D Leger,B Bioulac,P Philip,
Country
Year 2005
Numbers

Secondary Publication Information
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Extraction Form: Behavior - Design Details - INCLUDED Studies
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Design Details
Question... Follow Up Answer Follow-up Answer
Refid 15854855
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What outcome is being evaluated in this paper? Behavior
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What is the objective of the study (as reported by the authors)? To explore the association between sleep duration and daily caffeine intake in a working population. Caffeine acutely disrupts sleep in the laboratory, but the inter-relations between sleep and caffeine intake in daily life are ill-known.
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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) Questionnaire and diary based survey of 1498 persons from the GAZEL cohort of employees of the National Electricity and Gas Company (EDF-GDF) working in various locations in the Paris and South-West France areas. We analyzed total sleep time, our primary measure, and time in bed, both by sleep logs. We assessed daily intake of caffeine, consumption of alcohol and tobacco, use of hypnotics, and daytime somnolence, all by questionnaire.
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How many outcome-specific endpoints are evaluated? 1
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What is the (or one of the) endpoint(s) evaluated? (Each endpoint listed separately) sleep
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List additional health endpoints (separately).
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List additional health endpoints (separately)
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Notes measured as total sleep time (including time in bed, sleep latency, duration, and nocturnal awakenings).
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Clinical
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Physiological Physiological
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Other
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What is the study design? Cohort
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Randomized or Non-Randomized?
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What were the diagnostics or methods used to measure the outcome? Subjective
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Optional: Name of Method or short description questionnaire, self-report on sleep latency
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Caffeine (general) Caffeine (general)
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Coffee
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Chocolate
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Energy drinks
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Gum
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Medicine/Supplement
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Soda
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Tea
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Measured
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Self-report Self-report
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Children
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Adolescents
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Adults Adults
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Pregnant Women
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What was the reference, comparison, or control group(s)? (e.g. high vs low consumption, number of cups, etc.) caffeine was assessed as a total in mg by adding all the sources, but also converted into a number of cups of coffee
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What were the listed confounders or modifying factors as stated by the authors? (e.g. multi-variable components of models.  Copy from methods) age, gender, alcohol intake, smoking status and use of hypnotics
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Provide a general description of results (as reported by the authors). There were significant negative correlations between total sleep time and age (Pearson’s coefficient r=-0.081, P<0.01) and the number of daily cups of coffee (Pearson’s coefficient r=-0.058, P<0.05). To further examine the relationship between caffeine intake and total sleep time, we plotted the data (Fig. 1). On visual inspection, total sleep time remained unchanged for caffeine intake less than 8 cups/day, representing 97.8% of the population (Table 1). When caffeine consumption was less than 8 cups per day, there was no relationship between total sleep time and the number of daily cups of coffee (r=-0.004; P=0.87). Multiple linear regression analysis showed that the number of cups of coffee/day had no significant effect on total sleep time, after controlling for age, gender, alcohol intake, smoking status, and use of hypnotics. Only gender was a significant covariate in this model (Beta=0.064, P<0.05) (Table 3), but we found no interaction between caffeine intake and this variable. For subjects whose caffeine consumption was less than 8 cups/day, there was a significant negative Pearson’s correlation (r=-0.13; P<0.001). The multiple regression analysis (Table 3), adjusted for the same set of variables, showed that as caffeine increased, time in bed decreased (Beta=-0.125; P<0.001). Interactions with caffeine intake and the other variables were not significant. Sleep efficiency increased linearly (P<0.01) for caffeine intake increase from one to 7 cups per day (Table 1) in the multivariate analysis, as expected from the data concerning total sleep time and time in bed. For subjects whose caffeine consumption was more than 7 cups/day, mean sleep efficiency values were less consistent.
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Did the authors perform a dose-response analysis (or trend/related analysis)? No
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What were the authors's observations re: trend analysis?
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What were the author's conclusions? Our study shows that, in a working population of persons employed in the National Electricity and Gas Company (EDF-GDF), increasing caffeine intake up to 7–8 cups of coffee per day was not associated with a decreasing total sleep time. In subjects who consumed more than 8 cups of coffee, their total sleep time brutally decreased; however, this concerns only 2% of the population (31 persons). By contrast, the time subjects spent in bed was reduced as caffeine intake increased. As a result, sleep efficiency increased with caffeine intake. Despite the well-known acute effects of caffeine on sleep, habitual use of up to 7 cups of coffee (or 600 mg of caffeine equivalent) per day was not associated with decreased duration of sleep.
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What were the sources of funding? MSO was a visiting research fellow supported by a grant from University of Murcia.
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What conflicts of interest were reported? N/A
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Does the exposure (dose) need to be standardized to the SR? Multiple metrics
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Provide calculations/conversions for the exposure based on the decision tree in the guide (for all endpoints/exposure levels of interest). Authors state most analyses in terms of cups of coffee defined as 85 mg/cup. 7 cups coffee/day x 85 mg/cup = 595 mg/day 8 cups coffee/day x 85 mg/cup = 680 mg/day
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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 - NOAEL = 595 mg/day; LOAEL = 680 mg/day (decreased sleep duration)
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Notes regarding selection/listing of endpoints and exposures/doses to be compared to Nawrot. adverse effects on total sleep time seen at higher levels than in Nawrot.
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What is the importance of the study with respect to the adverseness of the outcome? Important
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