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Running head: LINKING TOGETHER CONSUMER KNOWLEDGE
Linking Together Consumer Knowledge
and the Effects of
Caffeine on Performance
Estella E. Nelson &
Amanda L. Taylor
Northwest Arkansas Community College
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Abstract
This study was conducted to evaluate the knowledge, beliefs, and behaviors of
physically active consumers in regard to effects of caffeine intake during performance. A
survey was conducted to identify the behaviors and beliefs of consumers. The study
surveyed active and very active individuals from local health clubs and university athletic
departments. Fifty surveys were completed and percentages from responses were
calculated.
Caffeine is a xanthine alkaloid compound found in coffee, tea, guarana, and
cocoa. Many food, beverage and dietary supplement products are formulated, marketed,
and purchased that contain caffeine. The survey conclude that 94% of physically active
consumers ages 18-52 consume coffee, soda beverages, tea, energy drinks, and energy
tablets. Sixty-four percent of the consumers believe that caffeine affects performance,
52% believe that caffeine enhances performance, yet only 32% of consumers caffeinate
prior to exercise.
The pharmacodynamics and the pharmacokinetics of caffeine are reviewed in
light of the survey findings. The surveys found that only 4 % respondents knew the
amount of caffeine in milligrams they consumed.
Studies have shown that caffeine does affect performance, in that it enhances
endurance. Interestingly, survey results showed that 52% of the physically active
consumers believe that caffeine enhances performance while 14% believe that it
decreases performance and 26% believe that caffeine did neither.
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An Overview of Caffeine
Caffeine is a central nervous system and metabolic stimulant. It inhibits
phosphodiesterase and has an antagonistic effect on central adenosine receptors
(Reynolds, 1989). Its effect on the central nervous system produces a condition of
wakefulness and increased mental activity (Reynolds, 1989).
The major sources of caffeine in the adult diet in North America are coffee (6075%) and tea (15-30%). Caffeinated soft drinks and chocolate are the major sources in
the diets of children (Nawrot, Jordan, Eastwood, Rotstein, Hugenholtz, Feeley 2003).
While not everyone likes coffee, tea, and colas, some turn to energy drinks. Some energy
drinks listed on surveys were Sobe No Fear, Rock Star, Enviga, N O Explode, and
Ripped To The Max.
With caffeine being so frequently ingested in foods, beverages, supplements, and
medications it is considered the most widely consumed psychoactive "drug" in the world
and probably one of the most commonly used stimulants in sports. (Magkos & Kavouras
2005) Also, caffeine may be administered in powder or tablets in doses of 100 – 300 mg
as in aspirin and other analgesics.
The International Olympic Committee has banned the use of large amounts of caffeine by
athletes, however smaller doses, as those found in common coffee and soda beverages are
permitted. The maximum permission concentration of caffeine in urine is 12μg per mL
(Martindale1989).
Chart 1 lists many common beverages and their approximate amounts of
milligrams per serving. Chart 2 describes the products used, the amount used, when, and
their knowledge of milligrams, by the consumers surveyed.
Chart 1: Commonly used products containing caffeine.
Caffeine content of select common food and
drugs[42][43]
Product
Caffeine
tablet
Excedrin
Serving size
Caffeine
per
serving
(mg)
1 tablet
200
1 tablet
65
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tablet
Coffee,
brewed
240 mL (8 U.S. fl
oz)
135*
Coffee,
decaffeinat 240 mL (8 U.S. fl oz)
ed
Coffee,
espresso
57 mL (2 U.S. fl oz)
5*
100*
Chocolate,
Dark
(Hershey's 1 bar (43 g; 1.5 oz)
Special
Dark)
31
Chocolate,
Milk
(Hershey
Bar)
1 bar (43 g; 1.5 oz)
10
Red Bull
250 mL (8.2 U.S. fl oz)
80
Cocaine
Energy
Drink
30 mL (1 U.S. fl oz)
100
250 mL (8.4 U.S. fl oz)
280
Rockstar
Energy
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Drink
Jolt Cola
29.57 mL (1 U.S. fl oz)
100
Bawls
Guarana
750 ml (1 bottle)
280
Soft drink,
Mountain
1 chocolate
Dew "Dew
100
Fuel"
Soft drink,
Coca-Cola 355 mL (12 U.S. fl oz)
54.5
Classic
Tea, green
255 mL (7 U.S. fl oz)
100
Tea, leaf or
bag
240 mL (8 U.S. fl oz)
15*
* Estimated
average caffeine
content per
serving. Actual
content varies
according to
preparation
240 mL (8 U.S. fl oz)
50*
Source: www.wikipedia.com
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Chart 2: Products consumed.
Product
Coffee
Soda Beverage
Tea
Energy Drink
Energy Tablet
% of
participants
(some may use
multiple
products)
28%
58%
34%
20%
4%
2+/day
users consume
prior exercise
participants that
knew
milligrams of
caffeine
7 participants
7 participants
6 participants
1 participant
1 participant
7 participants
11 participants
4 participants
7 participants
1 participant
1 participant
1 participant
1 participant
For individuals that are sensitive, caffeine in small amounts, such as a cup of
coffee, may cause nervousness and insomnia(Martindale1989) . Higher doses of caffeine
may cause medullary stimulation and convulsions (Martindale1989).
The chemical structure of caffeine is shown in Diagram 1. Other names for
caffeine are anhydrous caffeine, caffeine, caffeinum, guaranine, methylxanthines,
methytheobromine, and theine.
Diagram 1: The chemical structure of caffeine.
C8H10N4O2
Source: www.wikipedia.com
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Pharmacokinetics
Caffeine is absorbed readily after oral, rectal, parental administration, and through
the skin (Schonwald 2001) . It is absorbed from the gastrointestinal tract and peak
plasma levels occur in 45 minutes to 2 hours (Schonwald 2001). Caffeine is then
distributed rapidly into body water with an apparent volume of distribution of 1L/kg.
(Schonwald 2001)
The liver metabolizes caffeine to 3,7-theobromine, 1,3-theophyllline, and 1,7paraxanthine(Martindale1989) . These are metabolites of dimethylxanthines
(Martindale1989). Diagram 2 shows the chemical structures of the three primary
metabolites. Caffeine is excreted in urine, saliva, semen, and breast milk
(Martindale1989). The half-life (the time for the body to eliminate one half of the total
amount of caffeine consumed at a given time) of caffeine in normal adults is 3.0 to 7.5
hours (Schonwald 2001).
Diagram 2: Structure of the three primary metabolites.
Source: www.wikipedia.com
Pharmacodynamics
The methylxanthines have effects on the central nervous system, kidney, and
cardiac and skeletal muscle as well as smooth muscle (Martindale1989). Caffeine acts as
a stimulant towards the central nervous system (Martindale1989). It inhibits the enzyme
phophodiesterase and has an antagonistic effect at central adenosine receptors
(Martindale 1989) Caffeine is a ligand (a molecule that binds specifically to a receptor
site of another cell) that binds to surface cells of adenosine receptors without activating
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them (Katzung 1995). This reduces adenosine activity and increases the activity of the
neurotransmitter dopamine, which accounts for the stimulatory effect (Katzung 1995).
The methylxanthines have direct positive chronotropic and inotropic effects
(cardiovascular effects) on the heart (Katzung 1995). In unusually sensitive people
consuming a few cups of coffee may result in arrhythmias, but in most people,
consumption of higher doses of methylxanthines produces only sinus tachycardia and
increased cardiac output (Katzung 1995). .
The methylxanthines affect the gastrointestinal tract in that it stimulates
secretion of both gastric acid and digestive enzymes (Katzung 1995). The kidneys are
especially affected by theophylline as it is a weak diuretic (Katzung 1995). However, the
diuresis is not sufficient to be therapeutic (Katzung 1995).
Methylxanthines produce bronchodialation and is considered the major
therapeutic action (Katzung 1995). Other therapeutic actions of methylxanthines are
strengthening the contractions of isolated skeletal muscle in vitro and having potential
effects in improving contractibility and in reversing fatigue of the diaphragm in patients
with chronic obstructive lung diseases (Katzung 1995).
Caffeine and Exercise Performance
Caffeine is a naturally occurring substance ingested in a variety of forms,
and produces many hormonal, metabolic, and physiological effects throughout the body,
both at rest and during exercise (Magkos & Kavours 2005). It has been studied for its use
as a potential use as an ergogenic (increasing the capacity for mental and physical labor)
aid (Keisler & Armsey 2006). Several studies have demonstrated an improvement in
exercise performance in submaximal endurance activities (Keisler & Armsey 2006).
However, in high-intensity exercises, its potential ergogenic effect in acute, high intensity
exercise is unclear. Because of its potential use as an ergogenic aid, its use in sports is
regulated by most sanctioning bodies (Keisler & Armsey 2006).
When evaluating the effects of caffeine on individuals’ physiology and
performance, it is important to consider whether subjects are caffeine naïve or caffeine
tolerant (Reents 2000). In naïve subjects, caffeine increases epinephrine output in
proportion to dose (Reents 2000). Graham, Hibbert, and Sathasivam (1998) recently
found that caffeine ingested as capsules improved treadmill running by 31% compared to
placebo. When subjects ingested the caffeine from coffee, however, no increase in
performance was seen, despite a similar caffeine dose and equivalent caffeine plasma
concentrations” (Reents 2000).
Other researchers have studied specific activities in regards to caffeine
consumption. Berglund and Hemmingsson (1982) studied cross-country skiing and found
skiers ingesting 6mg/kg produced 1.7% improvement at an altitude of 300 m and a 3.2%
improvement in performance at 2900 m. Another study (Spriet et al. 1992) of cyclists,
single doses of 9 mg/kg caffeine consumed 1 hour prior to testing produced a 26.9%
increase in cycling time in recreational cyclists (Reents 2000).
Caffeine appears to offer ergogenic effects in prolonged endurance
exercise but not during activities that require very short bursts of high-intensity effort
(Reents 2000). For reasons that are unclear, caffeine consumed in capsules appears to
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produce a greater ergogenic response that equal quantities consumed in coffee (Reents
2000).
A more recent study (Stuart, Hopkins, Cood, & Cairns 2005) investigating
effects of caffeine in a performance test stimulating physical and skill demands of a
rugby union game. The conclusion was that caffeine was likely to produce substantial
enhancement of several aspects of high-intensity team sport performance (Stuart,
Hopkins, Cood, & Cairns 2005).
The results of caffeine ingestion “preloaded’ protocol involving 2 minute cycling
at 100% plus 1 minute of ‘all-out’ effort suggest that high intensity cycling performance
can be increased following moderate caffeine ingestion and that this improvement may be
related to a reduction in RPE and an elevation in blood lactate concentration (Doherty,
Smith, Hughes, Davison 2004).
Nancy Clark states, “Caffeine’s energy-enhancing effect is more likely related to
its ability to make exercise seem easier. Through its stimulant effect upon the brain,
caffeine may reduce the fatigue associated with long bouts of exercise. If you are
chronically tired from the rigors of your training program, you may be particularly
attracted to caffeine for this reduction in perceived exertion" (Clark 2003).
Author of Popular Sports Supplements and Ergogenic Aids, Mark S. Juhn (2003)
writes:
Generally speaking, the doses of caffeine used in studies
range from 2-9 mg/kg (about 250-700 mg caffeine), taken 1
hour or less prior to the event. Clearly, an ergogenic effect
of caffeine in aerobic activity is demonstrated in doses that
would not reach the disqualifying levels of NCAA and IOC
sport, as it takes approximately 9 mg/kg consumed to
achieve a urinary concentration of 12 µg/mL.
The use of caffeine is not surprisingly common. Caffeine
does not have the stigma branded to it that some
supplements do, and is quite safe. It is likely that many
Olympians use caffeine since the cut-off for
disqualification is considered high enough to warrant
taking the risk.
Survey Results
Table 1: Age of Survey Participants
18-24
25-29
30-34
35-39
72%
14%
6%
2%
40-44
0%
Table 2: Gender of Survey Participants
Male
46%
Female
54%
45-49
4%
50-54
2%
55-59
0%
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Table 3: Participants Rate of Activity Level
Not Active
Active
Moderately Active
0%
20%
44%
Table 4: Participants Days per Week of Exercise
1
2
3
4
12%
4%
18%
14%
5
36%
Very Active
36%
6
16%
7
0%
Table 5: Consumed caffeine prior to exercise.
Yes
No
32%
68%
Table 6: Consumption of caffeine prior to exercise made participant feel:
Anxious
Hyper
NonEnergized Other*
Drowsy
12%
16%
10%
* The option of ‘other’ was to be listed. Some comments were:
“its addicting, too many side effects”…”caffeine hinders my performance”…”I think it
causes cramps”…”it dehydrates me”…”it gives me a stomach ache when I work out”…”I
exercise early and drink coffee afterwards”…”I feel over anxious and
hyper”…”caffeinate beverages don’t hydrate very well”…”it helps have a bowel
movement”
Table 7: Does the consumer feel that caffeine does or does not effect performance?
Does
Does Not
Did Not Answer
64%
14%
10%
20 females / 17 males
2 females / 5 males
4 females /1 male
Table 8: How do you feel that consuming caffeinated beverages/products prior to
exercise effects performance?
Enhances
Decreases
Neither
Did Not Answer
52%
14%
30%
4%
Table 9: Do you feel that consuming caffeinated beverages/products prior to exercise
effect post exercise mood or energy level?
Yes
No
Did Not Answer
48%
40%
12%
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Table 10: Products consumed post exercise.
Products
% of participants
Coffee
8%
Soda Beverage
30%
Tea
18%
Energy Drink
4%
Energy Tablet
2%
2+
2 participants
1 participant
2 participants
Conclusion
Caffeine is a commonly used stimulant among athletes and active
individuals (Magkos & Kavours 2005). Caffeine can be derived from many sources of
food, energy drinks, supplements, and medications (Magkos & Kavours 2005).
Methylxanthines affect the central nervous system, cardiac and skeletal
muscle as well as smooth muscle (Magkos & Kavours 2005). Several studies have been
done to show that caffeine may have a positive effect on exercise endurance and
performance (Magkos & Kavours 2005).
The surveys indicate that the physically active consumer has an idea that caffeine
does enhance performance, however few participants knew how much caffeine they
actually consume. Soda beverages were the most popular product, while energy tablets
were the least popular. The majority of the physically active individuals surveyed
consumed caffeine. The majority believed that it did indeed enhance performance yet
only about one-third used it before they exercise.
Survey comments indicate that the caffeine beverages of choice seem to have too
many side effects such as, gastrointestinal distress, dehydration, anxiety, and addiction.
Caffeine may have some beneficial effects, however its use should be evaluated in
regard to the specific effect it may have the user while considering dosages amounts that
maximizes potential benefits and minimizes the risks or side effects.
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References
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Associates. p.101-102
Doherty, M., Smith, P., Hughes, M., Davison, R. (2004) Caffeine lowers perceptual
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