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

doi:10.1016/j.sleep.2004.10.005

Sleep Medicine

Volume 6, Issue 3, May 2005, Pages 247-251

https://doi.org/10.1016/j.sleep.2004.10.005 Get rights and content

Abstract

Objective/background

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.

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.

Results

Multiple linear regression analysis did not find a significant relationship between total sleep time and daily caffeine intake less than 8 cups of coffee per day, after controlling for age, gender, alcohol intake, smoking status, and use of hypnotics. By contrast, time in bed was reduced as caffeine intake increased (β=−0.125; P<0.001). Higher caffeine intake was not related to a higher daytime somnolence.

Conclusion

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.

Introduction

Caffeine is a widely used substance. It has been estimated that adults living in western societies have an average all-source daily caffeine intake of about 200–300 mg [1]. Within this dose-range and above, caffeine is thought to increase alertness, reduce sleep propensity and produce adverse effects in the central nervous system, such as insomnia. To date, most studies on the effects of caffeine intake have indicated that it has deleterious effects on sleep (increasing sleep onset latency, decreasing total sleep time and adversely affecting sleep quality), but this research has usually involved the administration of acute doses of caffeine near bedtime. Other studies which examine caffeine intake early in the morning also found significant reductions in total sleep time and sleep efficiency [2], [3], [4]. One of the limitations of these studies is that they are usually performed in laboratory contexts [5], [6], [7], [8], [9] and do not take into account the development of tolerance to chronic caffeine use [10], [11]. Therefore, the effects of acute doses of caffeine on sleep may not accurately reflect the effects of its chronic daily use. In addition, there are considerable inter-individual differences in response to caffeine intake [12], [13], possibly related to pharmacogenetic variability of caffeine metabolism [14]. To date, epidemiological description of sleep patterns in habitual caffeine users is limited. We therefore decided to address this topic in a French working population from data included in a larger study of health and lifestyle habits.

Section snippets

Participants

Participants were recruited from the GAZEL cohort, a long-term prospective study started in 1989, whose aim was to monitor the evolution of several health indicators in employees of the National Electricity and Gas Company (EDF-GDF) [15]. Four thousand eight-hundred thirty GAZEL participants were asked by mail to fill in a 3-week sleep log to investigate sleep schedules during working days, and to respond to other questions concerning lifestyle [16], [17]. Two thousand two-hundred sixty-five

Characteristics of the study sample

The study sample did not differ from the source sample with respect to main demographic parameters.

In our sample, 64% were male. Mean age was 51 (3.2) years (range 44–58 years). Employees were classified into three subgroups according to employment grade: low (blue-collar workers, clerks and craftsmen), intermediate (supervisors, foremen, and mid-level professionals) and high (senior managers, engineers and other senior professionals). Forty-nine percent were classified in the high-grade group,

Discussion

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. This absence of relationship is not affected by age, gender, alcohol status, smoking status or the use of sleeping pills. In subjects who consumed more than 8 cups of coffee, their total sleep time brutally decreased; however, this concerns only 2% of the

Acknowledgements

We thank all the subjects who participated in the study. Funding: MSO was a visiting research fellow supported by a grant from University of Murcia.

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Indeed, in a large community-based adult sample (33–45 years), sleep disturbance – i.e., insomnia complaints and short sleep duration – was found associated with heightened systemic inflammation five years later as represented by plasma CRP and IL-6, independently of several covariates [2]. We investigated the link between sleep characteristics and the genetic of pro-inflammatory cytokines in healthy subjects adding the analysis of daily caffeine consumption, as this one can interfere respectively with sleep and the inflammatory status [17,19,46]. In a large sample (1498 persons) of a French middle-aged (51 (3.2) years) working population (64% were male), reported sleep duration decreased but when caffeine intake exceeded 8 cups/d (680 mg/d), after controlling for age, gender, alcohol intake, smoking status, and use of hypnotics [46].
Pro-inflammatory cytokines are involved in sleep-wake regulation and are associated with caffeine consumption. This is a cross-sectional study in 1023 active French workers investigating associations between self-reported sleep complaints (>3months) and total sleep time (TST) with nine single-nucleotide-polymorphisms (SNPs) including pro-inflammatory cytokines, according to caffeine consumption. Participants were characterized as low, moderate and high (0–50, 51–300, and >300 mg/day) caffeine consumers. After adjusting the odd ratios (OR) for age, gender, and smoking, the risk of sleep complaints was higher in subjects with genetic mutations in tumor necrosis factor alpha (TNF-α, rs 1800629) (ORa [95%CI] = 1.43 [1.07–1.92] for both G/A and A/A aggregate genotypes) or interleukin-1 beta (IL-1β, rs1143627) (ORa = 1.61 [1.08–2.44] for homozygous A/A genotype), and the risk was higher when subjects carry the mutations in TNF-α plus IL-1β regardless of caffeine consumption. When stratified with caffeine consumption, the risk of sleep complaints was higher in TNF-α A allele carriers in high caffeine consumers, and in homozygous A/A genotype of IL-1β in moderate and high consumers. None of the nine SNPs influence TST, with the exception of the mutation on CYP1A2 and only when stratified with caffeine consumption. Our results also indicated more caffeine side-effects when carrying mutation on IL1β. This study showed that polymorphisms in TNF-α and/or IL-1β influenced sleep complaints but did not influence total sleep time. This suggests that management of sleep complaints, which can be addressed by clinical interventions, should consider the influence of the genetic profile of pro-inflammatory cytokines.
Associations between high caffeine consumption, driving safety indicators, sleep and health behaviours in truck drivers
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This group were not specifically targeted in the analysis due to the small sample size. However, extreme high levels of caffeine consumption have been shown to result in a dramatic decrease in total sleep time (Sanchez-Ortuno et al., 2005). Future research may wish to consider safety and health implications for extreme caffeine consumption.
Truck drivers are vulnerable to driver sleepiness due to pressures of shift work and prolonged driving hours; this is a safety concern as sleepiness more than doubles crash risk. Caffeine is a commonly used countermeasure to driver sleepiness. Previous research with truck drivers has demonstrated a positive impact of caffeine consumption on crash risk. However, habitual use of caffeine has the potential to impair night time sleep resulting in increased sleepiness and safety risk. One group that may be particularly vulnerable to the potential negative impacts of high caffeine consumption are those truck drivers who consume ≥ 5 caffeinated drinks per day (≥90th percentile American average daily caffeine consumption).
1,653 self-reported low (1 caffeinated drink per day) and 1,354 high (≥5 caffeinated drinks per day) caffeine consumers were compared across a range of driving safety indicators, health and sleep variables. All drivers completed an initial background questionnaire including the Epworth Sleepiness Scale (ESS), Berlin Questionnaire (BQ) and Dula Dangerous Driving Index (DDDI). Crashes and driving violations were monitored for up to 3 years (depending on enrolment date). Medical Examination Reports were available for 83.0% of the 3,007 participants.
High caffeine consumers were more likely to report poor sleep outcomes: shorter average sleep time, (7.08 h compared to 7.41 h), higher prevalence of excessive daytime sleepiness (7.5% compared to 5.7%) and higher proportion at high risk of obstructive sleep apnoea (OSA) on the BQ (13.1% compared with 9.4%). The higher caffeine consumers were more likely to report negative health behaviours: smoking, alcohol consumption, poor diet and infrequent exercise. Poorer driving safety indicators (negative emotions and aggressive driving on the DDDI) and previous crashes (27.8% compared to 21.6%) were also more common in high than low caffeine consumers.
Caffeine is an effective countermeasure to driver sleepiness, however, high caffeine consumers do not exhibit any benefit to driving safety indicators. In fact, there is some evidence for safety concern because high caffeine consumers self-report more crashes and worse driving safety indicators than low caffeine consumers. High caffeine consumption was associated with poor health behaviours. Further research is needed to fully understand the implications of high caffeine use. Interventions aiming to reduce truck driver sleepiness should be cautious in promotion of caffeine in isolation; a wholistic approach to improve driver health would likely be more effective than focusing on sleep health alone.
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Sleep Hygiene refers to a set of recommendations designed to maximize the ability to, and opportunity for, sleep. Despite its extensive use in primary care, especially for people with insomnia, the use of sleep hygiene, as a stand-alone therapy, in this population has been questioned. The aim of this chapter is to introduce the reader to the historical definitions of sleep hygiene, from its original definition to how it is operationalized and implemented today. In the second half of the chapter, we will move on to a broader discussion on the prevention of chronic insomnia. Unfortunately, as you will see, there is very little information on this latter topic. However, we have a good starting point theoretically, which is outlined, from which we can understand the development and trajectory of insomnia. The chapter concludes with a series of recommendations for the use of sleep hygiene, among other aspects, as preventative strategies.
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To date, one of the most heavily cited assessments of caffeine safety in the peer-reviewed literature is that issued by Health Canada (Nawrot et al., 2003). Since then, >10,000 papers have been published related to caffeine, including hundreds of reviews on specific human health effects; however, to date, none have compared the wide range of topics evaluated by Nawrot et al. (2003). Thus, as an update to this foundational publication, we conducted a systematic review of data on potential adverse effects of caffeine published from 2001 to June 2015. Subject matter experts and research team participants developed five PECO (population, exposure, comparator, and outcome) questions to address five types of outcomes (acute toxicity, cardiovascular toxicity, bone and calcium effects, behavior, and development and reproduction) in four healthy populations (adults, pregnant women, adolescents, and children) relative to caffeine intake doses determined not to be associated with adverse effects by Health Canada (comparators: 400 mg/day for adults [10 g for lethality], 300 mg/day for pregnant women, and 2.5 mg/kg/day for children and adolescents). The a priori search strategy identified >5000 articles that were screened, with 381 meeting inclusion/exclusion criteria for the five outcomes (pharmacokinetics was addressed contextually, adding 46 more studies). Data were extracted by the research team and rated for risk of bias and indirectness (internal and external validity). Selected no- and low-effect intakes were assessed relative to the population-specific comparator. Conclusions were drawn for the body of evidence for each outcome, as well as endpoints within an outcome, using a weight of evidence approach. When the total body of evidence was evaluated and when study quality, consistency, level of adversity, and magnitude of response were considered, the evidence generally supports that consumption of up to 400 mg caffeine/day in healthy adults is not associated with overt, adverse cardiovascular effects, behavioral effects, reproductive and developmental effects, acute effects, or bone status. Evidence also supports consumption of up to 300 mg caffeine/day in healthy pregnant women as an intake that is generally not associated with adverse reproductive and developmental effects. Limited data were identified for child and adolescent populations; the available evidence suggests that 2.5 mg caffeine/kg body weight/day remains an appropriate recommendation. The results of this systematic review support a shift in caffeine research to focus on characterizing effects in sensitive populations and establishing better quantitative characterization of interindividual variability (e.g., epigenetic trends), subpopulations (e.g., unhealthy populations, individuals with preexisting conditions), conditions (e.g., coexposures), and outcomes (e.g., exacerbation of risk-taking behavior) that could render individuals to be at greater risk relative to healthy adults and healthy pregnant women. This review, being one of the first to apply systematic review methodologies to toxicological assessments, also highlights the need for refined guidance and frameworks unique to the conduct of systematic review in this field.
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Aging, female sex, and urbanization increase the risk of sleep impairment. Sleep in urban-dwelling elderly African women has been sparsely studied. We studied the characteristics and correlates of sleep quality and habitual sleep duration in a primary care population of urban-living Nigerian women.
Sleep quality and sleep duration over the previous 1 month were estimated using the Pittsburgh Sleep Quality Index (PSQI). Excessive daytime sleepiness, risk of obstructive sleep apnea (OSA), and depressive symptoms were also assessed.
Of the 428 subjects included, 117 (27.3%) were poor sleepers endorsing PSQI scores >5, whereas 126 (29.4%) slept <7 hours. The poor sleepers were more likely to be obese (P = .022), to have a high risk for OSA (P = .013), and to have clinically significant depressive symptoms (P = .001) compared with the good sleepers. Habitual sleep duration of <7 hours was associated with past oral contraceptive use (P = .025) and a trend toward a higher likelihood of high risk for OSA (P = .05) and coffee consumption (P = .05). On regression, the odds of high risk for OSA were higher with poor sleep quality and sleep duration <7 hours, respectively, whereas the odds of coffee consumption were higher with sleep duration <7 hours.
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2017, Sleep Medicine Reviews
Caffeine is the most widely consumed psychoactive substance in the world. It is readily available in coffee and other foods and beverages, and is used to mitigate sleepiness, enhance performance, and treat apnea in premature infants. This review systematically explores evidence from epidemiological studies and randomized controlled trials as to whether coffee and caffeine have deleterious effects on sleep. Caffeine typically prolonged sleep latency, reduced total sleep time and sleep efficiency, and worsened perceived sleep quality. Slow-wave sleep and electroencephalographic (EEG) slow-wave activity were typically reduced, whereas stage-1, wakefulness, and arousals were increased. Dose- and timing-response relationships were established. The sleep of older adults may be more sensitive to caffeine compared to younger adults. Pronounced individual differences are also present in young people, and genetic studies isolated functional polymorphisms of genes implicated in adenosine neurotransmission and metabolism contributing to individual sensitivity to sleep disruption by caffeine. Most studies were conducted in male adults of Western countries, which limits the generalizability of the findings. Given the importance of good sleep for general health and functioning, longitudinal investigations aimed at establishing possible causal relationships among coffee- and caffeine-induced changes in sleep quality and health development are warranted.

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View full text

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

Abstract

Objective/background

Methods

Results

Conclusion

Introduction

Section snippets

Participants

Characteristics of the study sample

Discussion

Acknowledgements

Brain Res Brain Res Rev

Neurosci Biobehav Rev

Neuropsychopharmacology

Brain Res

Food Chem Toxicol

Chest

Behav Res Ther

The consumption of coffee

Effect of caffeine on physiological sleep tendency and ability to sustain wakefulness at night

Psychopharmacology (Berl)

Dose-related sleep disturbances induced by coffee and caffeine

Clin Pharmacol Ther

The health consequences of caffeine

Ann Intern Med

A naturalistic investigation of the effects of day-long consumption of tea, coffee and water on alertness, sleep onset and sleep quality

Psychopharmacology (Berl)

Biochemical mechanism of caffeine tolerance

Arch Pharm (Weinheim)

Pharmacological rationale for the clinical use of caffeine

Drugs