Caffeine consumption, insomnia, and sleep duration: Results from a nationally representative sample

Highlights

• Insomnia symptoms were associated with caffeine consumption in unadjusted models.

• Race/ethnicity and anxiety explain the association of insomnia symptoms and caffeine.

• Interaction between high caffeine and sleep duration was associated with non-restorative sleep.

Abstract

Objective

Insomnia symptoms have been individually associated with both caffeine consumption and sleep duration abnormalities in prior studies. The goal of this study was to determine whether caffeine consumption was associated with insomnia symptoms from a population perspective and whether this relationship depended on habitual sleep duration.

Methods

Data were extracted from the 2007-2008 National Health and Nutritional Examination Survey (N = 4730). Caffeine consumption was quantified as mg/d from 2 typical days of use, 7 to 10 d apart. Insomnia symptoms were evaluated using frequencies of difficulty falling asleep (DFA), difficulty staying asleep (DSA), non-restorative sleep (NRS), and daytime sleepiness (DS). Habitual sleep duration was assessed as the hours of sleep obtained on a typical night. Binomial logistic regression analysis evaluated the relationships of individual insomnia and sleepiness symptoms (DFA, DSA, NRS, and DS) with caffeine consumption and sleep duration variables, after adjusting for covariates.

Results

The mean ± SD caffeine consumption was 176.6 ± 201 mg/d. Mean habitual sleep duration was 6.8 ± 1.4 h. Insomnia symptoms were prevalent in 19.1% to 28.4% of the respondents. Although caffeine consumption was associated with all insomnia symptoms in the unadjusted models, the adjusted models demonstrated a trend toward significance with DSA. Sleep duration was inversely associated with the insomnia symptoms in unadjusted and adjusted analysis. Finally, NRS was associated with an interaction between increased caffeine consumption and sleep duration.

Conclusion

The association between caffeine use and insomnia symptoms depends on habitual sleep duration at a population level.

Introduction

Caffeine is one of the most frequently used psychoactive stimulant drugs. It is commonly used to ameliorate behavioral and cognitive performance deficits secondary to sleep deprivation [1], [2]. Caffeine's use has been associated with an improvement in performance in healthy individuals even at a low dose of 32 mg [3]. Caffeinated chewing gum at a dose of 100 mg showed an improvement in neurobehavioral functioning after subacute sleep deprivation when compared with placebo [4]. Caffeine has been shown to improve performance after sleep deprivation of ≥21 h [5], [6], [7], [8].

Despite its benefical effects on sleep deprivation, caffeine may have adverse sleep-related consequences on subsequent nights. These sleep disruptive effects may be broadly classified as insomnia symptoms and abnormalities of sleep disruption. Nocturnal use of caffeine may lead to increased worrying at night and sleeplessness [9]. Other subjective insomnia symptoms demonstrated after caffeine consumption in healthy individuals have included decreased total sleep time, difficulty falling asleep, increased nocturnal awakenings, and daytime sleepiness [10], [11], [12], [13]. Polysomnographic sleep abnormalities seen after caffeine consumption have included increased sleep latency, decreased stages 2 and 4 of non-rapid eye movement sleep, sleep fragmentation with brief arousals from sleep, and decreased sleep duration [11], [12], [13], [14], [15], [16], [17], [18]. These sleep-related problems may be amplified in individuals with insomnia.

In addition to the generation or aggravation of sleep continuity problems, consumption of coffee and other caffeinated drinks has been associated with insufficient duration of sleep or short sleep duration. Short sleep duration has been defined as a total sleep time of <6 h per night and has been associated with a wide range of medical and psychiatric comorbidities [19]. In college students, a mean caffeine consumption of 3 to 5 cups of coffee/d was associated with habitual sleep duration of ≤6 h a night [20]. Other studies have linked caffeine consumption to short sleep duration and insomnia symptoms in specific populations, such as deployed military personnel [2], middle-aged professional drivers (ages 49–64 y) [21], and college students [14]. In a study of military personnel, consumption of ≥3 caffeinated beverages was associated with a sleep duration of ≤3 h a night [2]. In another study, consumers of 5 cups/d of coffee had significantly reduced total sleep duration along with fragmented sleep [14]. These positive findings contrast with that of another epidemiologic study that showed no association between sleep duration and caffeine use in middle-aged women [22].

In summary, the relationship of daily caffeine use and sleep duration and insomnia symptoms is unclear, especially when both insomnia symptoms and sleep duration are considered simultaneously. Additionally, findings from laboratory-based studies may not be valid at the community level, where other covariates may play a role in this relationship. Thus, exploring these relationships at a population level will acquire significance for the following reasons:

• About one-tenth of the US population already suffers from insomnia [23], and insufficient sleep duration is a widely prevalent sleep-related condition.

• Caffeine is commonly used as a countermeasure for daytime consequences of inadequate sleep [2], [24].

• The population trends of caffeine consumption have increased exponentially over time since the arrival of and easy access to caffeinated energy drinks [25].

• Laboratory studies have demonstrated that caffeine consumption may be associated with insomnia symptoms, especially in individuals who report higher baseline anxiety levels.

Accordingly, in the present study, the relationship between habitual caffeine use and insomnia symptoms was evaluated using a nationally representative data set. We hypothesized the following:

• Heavier caffeine consumption, compared with light or no caffeine consumption, will be associated with higher insomnia symptoms and daytime sleepiness; and

• A higher probability of experiencing insomnia symptoms will be associated with an interaction between higher caffeine consumption and lower sleep duration.

The existence of such a complex relationship will expand the understanding of how caffeine consumption interacts with insomnia symptoms and sleep duration at a population level.