caffeine consumption, exercise, and sleep patterns final paper

The Relationship Between Exercise, Sleep Patterns, and Caffeine Consumption 1

The Relationship Between Exercise, Sleep Patterns, and Caffeine Consumption

Among 3rd Year College Undergraduates

Rob Errico

Psychology Department, Seattle University,

Seattle, WA

2011


Abstract

The current study examined the relationship between caffeine consumption, exercise routines,

and sleep patterns among 16 junior-standing undergraduate students enrolled full-time at a university in

northwestern Washington. General demographic information was gathered along with the participants'

average weekday caffeine consumption, number of hours slept on school nights, and average hours

exercised during the week. Employment information and extracurricular involvement was also included.

Running Spearman's rho analyses showed a significant positive association between number of hours

exercised and number of hours slept during the school week; Spearman's rho analyses also showed a

significant negative association between caffeine consumption and number of hours slept during the

school week. There was no significant association between caffeine consumption and number of hours

exercised. Future research could account for more factors such as participants' intensity of exercise,

caffeine content of beverages consumed, and confounding variables such as prescription medications

and physical disabilities. Lastly, future research should pool information from a much large sample size.


Introduction

There exists an intricate relationship between sleep patterns, exercise routines, and the quantity

of caffeine consumed by an individual. Each influences the other in ways that dramatically affect a

person’s overall physical and psychological health. Inadequate exercise leads to fatigue and poor

psychological functioning; poor psychological functioning may drive a person towards excessive caffeine

consumption which in turn leads to poor sleep. On the other hand, caffeine can boost psychological

performance, and can also increase exertion effort when exercising which lends to improved sleep

quality. For optimal health, a balance must be found. The relationships between caffeine, exercise and

sleep will now be examined more closely using relevant research.

Exercise positively affects sleep quality and diminishes sleep disturbances (Sin, Ho, & Chung,

2008; Digdon, 2007; Brand, et al., 2009) in addition to improving cognitive functioning (Brand et al.,

2009; Sin et al., 2008), emotional well-being (Brand et al., 2009; Digdon, 2007), and overall physical

health (Brand et al., 2009; Doherty & Smith, 2004). Better sleep generates improved cognitive

functioning (Brand et al., 2009), emotional well-being (Brand et al., 2009; Digdon, 2007), and physical

health (Brand et al., 2009; Doherty & Smith, 2004). Caffeine commonly serves as a method of coping

with sleepiness and general fatigue (Digdon, 2007; Sin et al., 2008). For some people, caffeine helps to

wake them up in the morning, especially 'night owls' - people with a late-night circadian preference

(Digdon, 2007). Caffeine attaches to adenosine receptors in the brain and inhibits their uptake of

adenine (Doherty & Smith, 2004). Adenosine receptors are partly responsible for our sleep-wake cycle

and also control levels of neural activity (Doherty & Smith, 2004). Caffeine acts as an ergogenic

(performance enhancing) and analgesic (pain suppressing) substance for both physical and mental

activity (Doherty & Smith, 2004). Caffeine is utilized more efficiently by a regular exerciser due to the


production of adenosine receptors throughout the body during and after physical exercise, thus resulting

in more receptors for caffeine to bind to (Doherty & Smith, 2004). With more receptors to bind to,

caffeine wakes up the user more and for a longer period as well as suppresses pain and improves

physical and cognitive performance more effectively. Excessive consumption of caffeine can cause poor

sleep or insomnia (Sin et al., 2008; Digdon, 2007). Based on the above articles, the most beneficial

interaction of all three factors involves a regular exercise regiment, a routine sleep pattern concordant

with personal circadian preference, and moderate caffeine consumption at least 4 hours before bedtime

to prevent sleep disturbances.

Because college students are the population in this study, the sample will likely comprise of

sleep-deprived individuals (Harris, 2009; Digdon, 2007). College is an obligation-filled and stressful

period in life and time-management has not always been mastered yet. In addition to time-

management, methods of coping with sleepiness are varied and not always conducive to physical and

mental health (Harris, 2009; Digdon, 2007). College students' ability to maintain healthy habits regarding

exercise, sleep, and caffeine may be frequently compromised by imposing priorities such as academic,

occupational, and extracurricular commitments.

Current research by Brand et al. (2009) on the relation between exercise and caffeine use

supports the theory that regular exercise facilitates healthy sleep patterns, improved psychological

functioning, and a decreased dependence on substances. However, a curious byproduct of researching

this relationship has revealed that caffeine has a marked positive affect on exercise endurance (Doherty,

2004). Nonetheless, the strong correlation between caffeine use and poor sleep quality should incite

special consideration when using caffeine for physical performance-enhancing purposes. With poor

sleep, reliance on substance abuse may follow, “either to induce sleep (alcohol, cannabis) or to reduce


daytime sleepiness (caffeine)” (Brand, et al., 2009, p. 133).

Despite the depth of each of the studies cited here regarding sleep patterns, exercise routines,

and caffeine consumption, there is a scarcity of research examining the interdependence of all three. The

present study seeks to reveal more about the delicate balance involved between healthy caffeine use,

exercise, and sleep patterns. College students vary in circadian preference, amount of sleep necessary

for normal psychological functioning, and tolerance to caffeine (Digdon, 2007). Despite these differences,

I hope to illustrate strong negative correlations between caffeine consumption and sleep as well as

strong positive correlations between exercise and sleep.

Methods

Participants

Junior year full-time college students enrolled at a private four-year university responded to a

questionnaire that was distributed through a combination of social networking sites, email

correspondence, and classroom visits. A total of 61 people were contacted and 16 questionnaires were

returned with signed consent forms. The data from all 16 questionnaires was complete and was used in

the present study; however, exercise information and caffeine consumption for 2 cases (#1 & #16) were

excluded from the analyses due to containing extreme scores.

The average age of the sample was 20.50 years (SD = .966). There were 6 males (37.5%) and 10

females (62.5%) who participated. The average GPA for fall quarter was a 3.19 on a 4.0 scale (SD = 2.43).

The average GPA for winter quarter increased to a 3.28 on a 4.0 scale (SD = 2.03). Participants in the

current study worked an average of 13.63 hours per week (SD = 9.71) and were involved in

extracurricular activities for an average of 8.69 hours (SD = 10.14).


Measures

Participants provided the hours of sleep they get for each night of the week. Only the hours slept

on nights during the school week were included in the data analysis. A School Night Sleep scale was

developed for the current study. It had good internal consistency, with a Cronbach’s alpha coefficient

reported of .771.

Information regarding exercise habits was gathered by asking participants the number of times

they exercise per week as well as the total number of hours they exercise per week.

The questions regarding caffeine were partitioned by beverage type (because of variations in

caffeine content) and when, during the week, they were consumed (during the school week or over the

weekend). This information was compiled to obtain a score that represented each participant’s overall

caffeine consumption during the school week. Weekend caffeine consumption was not included in the

data analysis.

The weekday caffeine consumption questions were investigated for internal consistency. The

scale earned a Cronbach’s alpha of .56. However, 25 cases were automatically excluded. In situations

where so few cases are considered, the mean inter-item correlation value can substitute as a reliable

determinant of a scale’s internal consistency. The inter-item correlation shows a score of .66 with values

ranging from .31 to 1.0. All scales' scores were averaged.

Procedure

The 27-item questionnaire asked about general demographic information, employment status,

and extracurricular involvement. Questions regarding caffeine consumption, sleep patterns, and exercise

habits were all aimed at gathering information about participants’ most recent trends in these areas.


Results

Preliminary Analyses

While the study began with the intention of having an equal distribution of males and females, it

later became apparent that this would not have made sense to do with the limited number of cases

collected. Therefore, no consideration was given to differences between genders despite literature

suggesting that males and females respond differently to caffeine consumption, exercise, and sleepiness

(Brand, et al., 2009; Doherty & Smith, 2004).

Case 16 had more than one declaration in two separate colleges (i.e., had 2 majors and 2

minors), so this information was excluded from the analysis due to the data analysis plan not having a

score that could account for this. Case 1's 'total number of hours exercised' score was excluded because

it appeared to be an outlier.

Hypothesis #1: Exercise is Associated with School Night Sleep Patterns

The relationship between the number of hours exercised per week and the total hours of sleep

during the school week was investigated using the Spearman’s rho correlation coefficient. There was a

strong, positive correlation between the variables, r(14) = .55, p <.05. See Figure 1 for a depiction of the

association. The number of hours exercised per week helps to explain nearly 30.25% of the variance in

participants' total hours of sleep during the school week.

Hypothesis #2: School Week Caffeine Consumption is Associated with School Night Sleep Patterns

The relationship between the total number of caffeinated drinks consumed during the school

week and the total number of hours of sleep during the school week was investigated using the

Spearman’s rho correlation coefficient. There was a strong, negative correlation between the variables,

r(14) = -.51, p <.05. See Figure 2 for a depiction of the association. The total number of caffeinated drinks


consumed during the school week helps to explain 26.01% of the variance in participants' total number

of hours of sleep during the school week.

Discussion

The current study's findings supported existing research that adequate exercise encourages

healthy sleep patterns. Research points to the positive impact regular exercise has on psychological

functioning, emotional well-being, and perceived levels of energy (Brand et al., 2009) suggesting that

those who get adequate exercise would desire smaller average quantities of caffeine – although there

are many exceptions to this extrapolation. Digdon (2008) says that some people are considered evening

types, also known as 'night owls', according to their circadian preferences. Night owls prefer to stay up

late and wake up late, so, for them, caffeine serves as a crucial component for early-morning functioning.

The majority of college students fall in the night owl category (Digdon, 2008) and caffeine is very

important for them, especially those with early classes. However, the effects of caffeine fade after 4

hours (Sin et al., 2008) so morning-time caffeine consumption alone does not explain how caffeine is

such a prevalent culprit of sleep disturbance (Digdon, 2008). The current study showed that people who

exercised less also slept less and that people who slept less consumed more caffeine.

Research indicates that sleepiness is the most common reason for caffeine consumption (Digdon,

2008). Personal traits that cause poor sleep for college students include an unfavorable attitude toward

life, poor self-confidence, negatively oriented mental and physical arousal (i.e. tense, irritable, or

nervous), unfavorably aggressive behavior (i.e. internalizing, over-controlling, or evasive), negative self-

perception of body sensations, unfavorable focusing habits, and unfavorable rumination habits (Brand et

al., 2009). According to Brand (2009), athletes who engage in vigorous exercise on a regular basis

experience less daytime sleepiness, less depression and anxiety, more positive psychological well-being,


and have higher self-esteem. These findings suggest that the psychological causes of poor sleep are

remedied by the powerful benefits exercise has on quality of sleep. This may be because exercise causes

an increase in slow wave sleep, a reduction in light sleep, and shortened sleep onset latency (the time it

takes to fall asleep after closing one's eyes) (Brand et al., 2009). Accordingly, those who do not get

adequate exercise would need to resort to other means to get these benefits. This helps to explain the

link between exercise and caffeine consumption, despite the current study failing to find a significant

association between the two. If participants were not getting adequate exercise, they appeared to rely

more on caffeine to make up for poorer psychological functioning, less energy, and poorer sleep

patterns.

Literature on the topic of exercise and sleep generally advocates for athleticism (being on a

sports team, or having an exercise regimen that is strictly adhered to by the individual on his or her own)

(Brand et al., 2009; Doherty & Smith, 2004). Athletes may experience better sleep quality due to “a more

structured wake/sleep pattern, which normally promotes healthy sleep” (Brand et al., 2009, p. 140).

Athletes often have trainers, physicians, psychologists, or various other forms of social support that

“contribute to a more structured life, very likely including sleep patterns” (Brand et al., 2009, p. 140).

These aspects ultimately play into the theme of the importance of time-management. A structured life

allows for a more efficient utilization of time and can prevent the disruption of sleep patterns and

exercise routines. Lastly, athletes are usually knowledgeable about the importance of good sleep for

physical and mental recovery after exhausting exercise (Brand et al., 2009). This is in concordance with

the current study's findings showing that participants involved in sport-related extracurricular activities

or those who were committed to 5 hours or more of weekly exercise reported regular sleep patterns (i.e.

a consistent 7 or 8 hours of sleep over the entire week) as opposed to other participants who reported


irregular sleep patterns.

Digdon (2007) explores the topic of being knowledgeable about personal physical and mental

health in an article examining how circadian preference can determine the methods used by college

students to cope with sleepiness. “Circadian preferences are influenced by the endogenous (internal)

circadian pacemaker, ‘zeitgebers’ such as exposure to light (external cues that synchronize an organism's

internal clock to the Earth's 24 hour light/dark cycle), behavioral rhythms, lifestyle obligations and

choices, and developmental maturation” (Digdon, 2007, p. 417). As mentioned before, college students

are predominantly evening types (Digdon, 2007). 'Night owls' engage in less physical activity, rely on

caffeine more often, and get less natural light than intermediate or mornings types, also known as 'Larks'

(Digdon, 2007). As these night owls develop ways to cope with sleepiness, bad habits are easily formed

(Digdon, 2007). As habits take root, a willingness to try viable alternatives diminishes and thus caffeine

becomes the most common method of coping with sleepiness while exercise and spending time

outdoors are rated as less and less effective (Digdon, 2007). “College students who are evening types

have different beliefs about methods for coping with sleepiness than college students who are

intermediate [or morning types] in circadian preference” (Digdon, 2007, p. 423). In the current study,

those who reported less than 6 hours of sleep a night or slept a total of 30 hours or less over the course

of the school week also reported significantly higher caffeine use (8 or more caffeinated beverages per

school week) and unsatisfactory exercise habits (2 hours or less a week). There were no exceptions, 30

hours of sleep appeared to be the cutoff point for healthy caffeine use and adequate exercise. The

insidious nature of caffeine addiction is revealed by night owls' sleepiness ratings as no sleepier than

intermediate types despite getting quantitatively less sleep and sleep of poorer (subjective) quality. This

is due to caffeine providing them a sense of temporary relief from their actual fatigue (Digdon, 2007).


Digdon (2007) speculates that perhaps night owls are quite aware of the dangers their coping methods

pose:

Perhaps sleepiness is considered a necessary consequence of ambition and of getting ahead in

an individualistic, competitive society. If this is the case, it may lessen student motivation to

eliminate sleepiness, especially if students also underestimate the negative effects of sleepiness

on performance (p. 424).

Knowing about healthy sleep habits, healthy methods of coping with sleepiness, and one's own

convictions about the effectiveness of each coping method all help to maintain the proper balance

necessary for healthy and responsible caffeine use. Although the present study did not ask about

participant's ratings of their sleepiness or opinions about the coping methods they use, their habits were

apparent by the information they reported: sleep-deprived participants neglected to exercise enough

[or, perhaps, vice a versa – the study suggests only association, not causation] and relied heavily on

caffeine.

Limitations

The results of the current study must be cautiously considered due to several limitations. The

most significant limitation of this study is its very small sample size. A total of 61 questionnaires were

distributed but only 16 were returned. For both analyses that were run to examine the research

hypotheses, only 14 cases were considered. Furthermore, the samples themselves represented only

junior-standing college students. Thus, the generalizability of this study's results is quite small.

Other limitations arose from the questionnaire's simplicity. The study did not account for

prescription medications; a significant confounding variable in this category would be pharmaceutical

stimulants. Likewise, there were no questions regarding learning disabilities, psychological disorders, or


physical disabilities that may have explained why some participants seemed to neglect getting adequate

exercise or had poor sleep patterns. For example, chronic depression is known to cause insomnia in

some cases (Brand et al., 2009 & Digdon, 2007).

In a similar vein, questions regarding participant's circadian preferences and school/CRO

schedules would have helped explain sleep patterns and caffeine use where getting adequate sleep or

exercise may have been very difficult with certain schedules and may have been conflictual with other

commitments – thus representing circumstantial restrictions rather than a participant purposefully

neglecting exercise or sleep.

The rigorousness of exercise and the stress level of participant's lives were not accounted for –

both of which effect quality of sleep and likelihood of caffeine reliance. The results of this study did not

account for gender differences and this presents another limitation to the findings. Females and males

respond differently to vigorous exercise as well as the effects of caffeine (Brand et al., 2009 & Doherty &

Smith, 2004). Tolerance to caffeine may have also effected the accuracy of the findings because some

individuals who were consuming several cups of caffeinated beverages a day may have reached a level of

tolerance that caused them to only feel the effects as much as an infrequent caffeine drinker consuming

one cup or less a day. Similarly, the caffeine beverage index could have been inaccurate due to caffeine

content variations across different beverage venders (i.e. a cup of coffee from Starbucks compared to a

cup from 7-11).

Conclusion

Adequate exercise is associated with healthy sleep patterns. Adequate sleep is associated with

healthful and responsible caffeine consumption. Because college students vary in their circadian

preference and school schedules, which sometimes conflict, caffeine can serve as a helpful means of


remaining awake and alert throughout the morning. When it is not required for normal functioning (aka,

when user is not addicted), it appears that moderate caffeine consumption can be used for its analgesic

and ergogenic properties at least 4 hours before bedtime without significantly affecting sleep patterns or

exercise routines (Doherty & Smith, 2004). While this is not nearly a large enough sample to safely

generalize to the greater college population, the results from this study suggest that the ideal balance is

as follows: per school week, junior year college students should get at least 5 hours of exercise, 35 hours

of sleep, and consume no more than 5 caffeinated beverages. Why not suggest students get a full nine

hours of sleep per night, exercise at least one hour every day and consume caffeine only when

necessary? As mentioned before, most college students are 'night owls' in their circadian preference, are

sleep-deprived because of many commitments, responsibilities, and circumstantial disadvantages and

distractions, and are in the process of adjusting to adult life. Thus, an 'ideal balance' must remain

realistic by accounting for all the time-consuming factors in a college student's life while striving to make

the best of what limited time they have. Future research can address the limitations of this study by

administering a more comprehensive questionnaire to a larger population, and perhaps follow up with a

second questionnaire several months later to account for differences in sleep patterns and exercise

habits in response to different schedules and the maturation of participant's methods of coping with

sleepiness.


References

Brand, S., Gerber, M., Beck, J., Hatzinger, M., Puhse, U., & Holsboer-Trachsler, E. (2009). High exercise

levels are related to favorable sleep patterns and psychological functioning in adolescents: A

comparison of athletes and controls. Journal of Adolescent Health. 46(2010), 133-141. doi:

10.1016/j.jadohealth.2009.06.018

Digdon, N. L. (2007). Circadian preference and college student beliefs about how to cope with sleepiness.

Biological Rhythm Research, 39(5), 417-426. doi: 10.1080/09291010701590067

Doherty, M., & Smith, P. M. (2004). Effects of caffeine ingestion on rating of perceived exertion during

and after exercise: A meta-analysis. Scandinavian Journal of Medicine & Science in Sports.

15(2004), 69-78. doi: 10.1111/j.1600-0838.2005.00445.x

Harris, K. M. (2009). Caffeine consumption as a predictor of sleep quality, sleep hygiene, subjective

sleepiness, and academic performance among north texas female college students. Retrieved f

rom Texas Woman's University Dissertations. (T2009 h313c)

Sin, C., W., M., Ho, J., S., C., & Chung, J., W., Y. (2008). Systematic review on the effectiveness of caffeine

abstinence on the quality of sleep. Journal of Clinical Nursing, 18, 13-21. doi: 10.1111/j.1365-

2702.2008.02375.x


Figure 1

Exercise Routine is Positively Associated With School Night Sleep Pattern (N=14)

Note: Outlying score of 25 hours of exercise per week has been omitted. Significant difference at the .05

level


Figure 2

School Week Caffeine Consumption is Negatively Associated With School Night Sleep Pattern (N=14)

Significant difference at the .05 level

caffeine consumption, exercise, and sleep patterns final paper

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