Caffeine and Energy
Jay R. Hoffman, PhD
Department of Health and Exercise Science, The College of New Jersey, Ewing, New Jersey
RECENT RESEARCH HAS INDI-
CATED THAT ENERGY DRINKS ARE
THE MOST POPULAR SUPPLEMENT
BESIDES MULTIVITAMINS IN THE
AMERICAN ADOLESCENT AND
YOUNG ADULT POPULATION.
MORE THAN 30% OF ALL AMERI-
CAN MALE AND FEMALE ADOLES-
CENTS USE THESE SUPPLEMENTS
ON A REGULAR BASIS. ENERGY
DRINKS ARE ALSO REPORTED TO
BE THE MOST POPULAR SUPPLE-
MENT (41.7% OF THE 403 ATH-
LETES SURVEYED) AMONG
YOUNG (17.7 62.0 YEARS) ELITE
BRITISH ATHLETES. THIS BRIEF
REVIEW WILL EXAMINE THE EFFI-
CACY OF THESE ENERGY DRINKS
REGARDING PERFORMANCE IM-
PROVEMENTS AND METABOLIC
ENHANCEMENT. IN ADDITION, IS-
SUES RELATING TO THE SAFETY
OF ENERGY DRINK CONSUMPTION
WILL ALSO BE DISCUSSED.
Recent research has indicated
that energy drinks are the most
popular supplement besides
multivitamins in the American adoles-
cent and young adult population
(17,28). More than 30% of all American
male and female adolescents use these
supplements on a regular basis. Energy
drinks are also reported to be the most
popular supplement (41.7% of the 403
athletes surveyed) among young
(17.7 62.0 years) elite British athletes
(40). The primary reason for their use is
thought to be related to a desire for
reducing or controlling body fat
(6,13,17,28). However, many competi-
tive athletes also use these energy
drinks for their potential ergogenic
effect. The basic active ingredient in
these energy drinks is caffeine, and
although ergogenic beneﬁts have been
seen with caffeine supplementation in
doses ranging from 3 to 9 mgkg
(equivalent to approximately 1.5-3.5
cups of automatic drip coffee in a 70-kg
person), there does appear to be
a difference in the ergogenic potential
when caffeine is ingested in a food
source (coffee or sports drink) com-
pared with its anhydrous form.
Although both forms have been shown
to provide an ergogenic effect, the
magnitude of performance improve-
ments appears to be greater when
caffeine is ingested in tablet form
(21). To maximize the effectiveness of
caffeine in an energy drink, supplement
companies will often add several addi-
tional ingredients to exacerbate the
stimulatory potential of caffeine. This
brief review will examine the efﬁcacy of
these energy drinks regarding perfor-
mance improvements and metabolic
enhancement. In addition, issues re-
lating to the safety of energy drink
consumption will also be discussed.
ENERGY DRINKS AND WEIGHT
Caffeine alone has been demonstrated
to be effective in enhancing lipolysis,
fat oxidation, and reducing glycogen
breakdown (1,15); however, when it
is combined with other thermogenic
agents, its effectiveness appears to be
magniﬁed (12,27). Caffeine, in combi-
nation with ephedra, has been shown
to be an effective supplement for
increasing metabolic rate and stimulat-
ing fat loss (8,23). However, as a result
of the Federal Drug Administration’s
ban on ephedrine alkaloids in 2004, the
use of alternative therapeutic means
to combat obesity has also been exam-
ined. Synephrine is a mild stimulant
and is thought to contribute to appetite
suppression, increased metabolic rate,
and lipolysis (18). To maximize its
effectiveness as an effective weight loss
supplement, it appears that synephrine
may need to be combined with
other herbal products (26). Some of
these products may include yohimbine,
yerba mate extract, hordenine, phen-
ylethylamine, and methyl tetradecylth-
ioacetic acid. All of which have been
shown to play a role in enhancing
lipolysis and increasing energy expen-
diture (3,5,19). However, many of these
additive ingredients are used for dual
purposes. For instance, phenylethyl-
amine is an endogenous neuroamine
that is often included in weight loss
supplements to enhance mood. Several
studies have shown that phenylethyl-
amine can relieve depression and
improve mood in clinical populations
(24,46). Whether these ingredients
can enhance mood in an apparently
healthy population is not well estab-
lished. A recent examination of an
energy drink containing several ingre-
dients including phenylethylamine was
unable to demonstrate any signiﬁcant
effect on mood state (32).
A recent study examined the thermo-
genic effect of an acute ingestion of an
energy drink marketed as Redline Prin-
cess (Vital Pharmaceuticals, Inc.,
sports nutrition; supplements; ergogenic
Copyright ÓNational Strength and Conditioning Association Strength and Conditioning Journal | www.nsca-lift.org 15
Davie, FL) (32). The supplement con-
tained ahost of ingredients that included
caffeine, beta-alanine, vitamin C, beta-
phenylethylene, hordenine HCL,
evodiamine, N-methyl tyramine, 5-
hydroxytryptophan, potassium citrate,
vinpocetine, yohimbine HCL, and St.
John’s wort extract. Results of the study
indicated that acute ingestion of the
supplement enhanced fat utilization, as
reﬂected by a greater caloric expenditure
from fat (see Figure 1). Other studies
have shown that an acute ingestion
of a supplement containing caffeine,
citrus aurantium, garcinia cambogia,
and chromium polynicotinate can
signiﬁcantly increase caloric expendi-
ture (30,49). These multi-ingredient for-
mulations do appear to be effective in
stimulating metabolic changes. The role
thateach ingredient contributesthough is
not well understood. Part of the problem
in understanding individual contribution
of these ingredients is related to the
proprietary nature of the ingredient
panel. To maintain a competitive advan-
tage, sport supplement companies are not
apt to disclose speciﬁc ingredient con-
centrations and tend to group various
ingredients as speciﬁc ‘‘matrixes.’’
The effect of prolonged consumption
of energy drinks on weight loss has
shown some promising results. In
a clinical examination, Boozer et al.
(8) have reported signiﬁcant decreases
in body mass and body fat, with
positive alterations to lipid proﬁles
following 6 months of using an ephed-
rine and caffeine supplement. Providing
further support, an additional study
examining a combination of ephedra,
caffeine, omega-3 fatty acids, and
several vitamins for 9 months in
women showed signiﬁcant decreases
in body mass, body fat, and improve-
ments in various metabolic indices such
as insulin sensitivity and lipid proﬁles
(25). The beneﬁcial effect of energy
drinks in short-duration studies and
without the use of ephedra compounds
has also been reported. Roberts and
et al. (44) demonstrated that following
28 days of consuming the energy drink
Celsius (containing 200 mg caffeine,
guarana extract, green tea leaf extract,
glucuronolactone, ginger extract, and
taurine), a signiﬁcant decrease in body
fat and body mass in healthy college-
aged athletes was seen. These beneﬁcial
effects observed for the multi-ingredient
energy formulations have been dem-
onstrated without concomitant alter-
ations to diet or exercise habits.
Whether the addition of energy drink
consumption to a dietary and exercise
intervention can exacerbate weight and
body fat loss is not well understood. In
consideration of the large obesity
epidemic within the United States
(48), additional research appears war-
ranted to determine whether energy
drinks can play a signiﬁcant role, in
combination with dietary and exercise
intervention, in the treatment options
associated with weight loss.
ENERGY DRINKS AND ATHLETIC
Energy drinks are often used by
athletes as a pre-exercise or pre-game
supplement to either enhance the
quality of their workout or improve
athletic performance. Although caf-
feine has been used as an ergogenic
aid for many years, consistent beneﬁts
have only been seen during endurance
activities, in which time to exhaustion
is often reported to increase
(14,20,21,31). This delay in fatigue is
thought to be related to caffeine’s
ability to alter exercise metabolism by
enhancing fat oxidation, thereby pre-
serving muscle glycogen content (47).
Although caffeine has also been sug-
gested to augment strength and power
performance by enhancing muscle
contraction efﬁciency through acceler-
ated mobilization of intracellular cal-
cium ions from the sarcoplasmic
reticulum (35) and/or by enhancing
glycolytic regulatory enzyme kinetics
(47), evidence demonstrating its ergo-
genic beneﬁt during anaerobic perfor-
mance has been limited.
Figure 1. Average 3-hour caloric expenditure from fat. *Signiﬁcant difference (p,0.05) between the supplement Redline Princess
and placebo. Data are reported as mean 6SD.
VOLUME 32 | NUMBER 1 | FEBRUARY 2010
Caffeine and Energy Drinks
To increase the ergogenic potential of
energy drinks, caffeine is often com-
bined with other ingredients to provide
a synergistic effect and increase the
probability of a performance response.
Several recent studies have demon-
strated that a pre-exercise energy
supplement can delay fatigue and
improve the quality of a resistance
training workout (31,33,41). The com-
bination of 450 mg of caffeine, 1,200
mg of garcinia cambogia (50% hydrox-
ycitric acid), 360 mg of citrus auran-
tium extract (6%), and 225 mgof
chromium polynicotinate in an en-
riched coffee drink was shown to
signiﬁcantly enhance time to exhaus-
tion during cycle ergometer exercise by
29% compared with subjects consum-
ing decaffeinated coffee (31). However,
within the same study, no difference
in anaerobic power performance was
noted between the consumption of
the supplement and placebo (decaf-
feinated coffee). These results were
similar to another study that showed
that an energy supplement (Red Bull
energy drink; Red Bull GmbH, Fuschl
am See, Austria) increased upper-body
muscle endurance but had no effect on
power performance during repeat
Wingate anaerobic power tests (16).
Improvements in the volume of
training (deﬁned as total number of
sets 3repetitions in a workout) from
an energy drink were also conﬁrmed
by a recent study by Hoffman et al.
(33). They showed that an energy
drink containing 110 mg of caffeine,
1,500 mg of L-taurine, 350 mg of
glucuronolactone, and 5.2 g of
branched-chain amino acids consumed
10 minutes before a resistance exercise
session enhanced acute exercise per-
formance by increasing the number of
repetitions and the total volume of
exercise performed during that training
session. The greater volume of training
was also shown to augment both the
growth hormone and the insulin
response to exercise, indicating that
consumption of this pre-exercise en-
ergy supplement enhanced the ana-
bolic response to the training session.
Energy drinks improve endurance per-
formance and the quality of a resistance
exercise workout; however, many ath-
letes use energy drinks primarily for its
stimulatory effect, speciﬁcally to en-
hance focus, alertness, and reaction time.
The datato support this effectare limited
but they do provide evidence to support
many of these empirical claims made by
athletes. The popular energy drink Red
Bull has been shown to enhance cogni-
tive performance through improved
choice reaction time, concentration,
and memory, which reﬂected an im-
proved alertness (2). Recently, Hoffman
et al. (29) examining an energy drink
containing caffeine and a number of
additional herbal and botanical com-
pounds that included evodiamine,
N-acetyl-L-tyrosine, hordenine, 5-
hydroxytryptophan, potassium citrate,
N-methyl tyramine, sulbutiamine, vin-
pocetine, yohimbine HCL, and St.
John’s wort extract (marketed as Redline
Extreme; Vital Pharmaceuticals, Inc.,
Davie, FL) reported signiﬁcant increases
in focus, alertness, and reaction time.
Improvements in reaction time (see
Figure 2) were assessed through both
visual and auditory stimuli. Interestingly,
despite a signiﬁcant improvement in
reaction ability, no signiﬁcant improve-
ments were noted in anaerobic power
performance as assessed by repeated
Wingate anaerobic power tests.
SAFETY ISSUES RELATED TO
ENERGY DRINK CONSUMPTION
As mentioned earlier, caffeine is a mild
stimulant and is commonly found in
coffee, tea, chocolate, and soft drinks.
The concentration of caffeine in these
products has been reported to range
from 40 to 150 mg (37). In contrast, the
top selling energy drinks have caffeine
levels that range from 75 to 174 mg per
Figure 2. Reaction time: Average percentage of successful hits from total possible targets.*Signiﬁcant difference (p,0.05) between
the supplement Redline Extreme and placebo. Data are reported as mean 6SD.
Strength and Conditioning Journal | www.nsca-lift.org 17
serving, while in some of the higher
caffeine energy drinks, levels may
exceed 500 mg per serving (42). The
adverse effects seen with caffeine in
these doses include insomnia, nervous-
ness, headache, and tachycardia (9).
However, changes in the blood pres-
sure response have been inconclusive.
Several studies have reported signiﬁ-
cant elevations in systolic blood pres-
sure (30,49), while others have shown
no change (2,10,32,45). Differences
between the studies are not clear, but
they are likely related to differences
within the combination of ingredients
that are generally associated with these
energy drinks. These studies have
consistently shown no alterations in
diastolic blood pressure. Interestingly,
a recent discussion of the safety issues
associated with energy drinks sug-
gested that the products that are
generally added to these supplements
such as guarana, ginseng, and tuarine
are in concentrations that are far below
the amounts associated with adverse
events (9). However, in energy drinks
that contain ephedra alkaloids or other
b-agonists such as citrus aurantium
(e.g., synephrine), a higher risk for an
exaggerated sympathetic response may
Several case reports have indicated
that energy drinks may increase the
risk for ventricular tachycardia (38) or
myocardial ischemia (7). However, a
European study has reported no asso-
ciation between caffeine consumption
and cardiac conduction abnormalities
(36). A health concern though has
been raised if energy drinks are con-
sumed with alcohol. A recent study has
reported a blunted cardiac autonomic
control in healthy subjects consuming
energy drinks mixed with alcohol (50).
Although no signiﬁcant arrhythmias
were reported, the authors suggested
that individuals who were predisposed
to arrhythmia may be at an increased
risk for a signiﬁcant adverse event if
they combine alcohol with an energy
A concern that energy drinks can
increase the risk for dehydration was
raised based on evidence that caffeine
can induce diuresis and natriuresis (43).
However, in several well-designed
studies, caffeine consumption has not
been shown to impair hydration,
exacerbate dehydration, or impair
thermoregulation (11,22). In a recent
review of the literature, Armstrong
et al. (4) have surmised that caffeine
does not reduce exercise-heat toler-
ance or increase the risk for hyperther-
mia. However, it should be
acknowledged that energy drinks that
contain ephedra or other b-agonistic
compounds may not have the same
benign risk. Several well-documented
heat deaths of professional athletes
who were using ephedra had resulted
in part to the banning of that herbal
ingredient in 2004. It may be prudent
to advise against the use of energy
drinks that contain these ingredients
in individuals who are poorly condi-
tioned, overweight, and exercising in
Additional concerns recently raised
about energy drinks surround the
issues relating to dependence, with-
drawal, and tolerance (42). Although
many of these issues have been studied
with caffeine, direct studies with en-
ergy drink consumption are limited.
There is considerable debate whether
caffeine can produce a dependence
syndrome that is similar to that
associated with a narcotic. A few
studies have suggested that habitual
caffeine users may fulﬁll diagnostic
criteria for substance dependence
(34,39); however, there is no evidence
to suggest such behaviors in individuals
consuming energy drinks. The issue
of withdrawal has been noted in more
than 60 studies published in the
medical literature in the past 10 years
(42). Symptoms such as headache,
tiredness/fatigue, sleepiness, and irri-
tability are associated with caffeine
withdrawal. How this is affected by
energy drink consumption is also not
well understood. The issue of tolerance
is a major concern for athletes who use
energy drinks on a regular basis during
their competitive season. In athletes
who play on a daily basis such as in
baseball, the issue of tolerance may
have important implications as the
season progresses. Although high
caffeine ingestion has been associated
with tolerance (42), there are no
studies to date that have examined
the issue of tolerance in energy drinks.
Energy drinks are the most popular
supplement being used by young adult
and athletic populations today.
Although caffeine is the primary active
ingredient in these drinks, the combi-
nation of various other ingredients
including herbal and botanical com-
pounds makes it quite difﬁcult to
provide a general statement of efﬁ-
ciency for energy drinks. The answer
regarding the efﬁcacy and risk associ-
ated with an energy drink is speciﬁc to
the ingredients within each respective
supplement. Based on a number of
studies examining various energy drink
formulations, the efﬁcacy of these
supplements has been established
regarding improvements in exercise
endurance (e.g., delaying fatigue).
However, ingestion of energy drinks
does not appear to provide any
signiﬁcant effect on strength and
power performance but does appear
to enhance the quality of a resistance
training workout. In addition, many
strength/power athletes use energy
drinks for their stimulatory potential.
Ingestion of these drinks has been
shown to enhance alertness, focus,
and reaction time to various stimuli.
Energy drinks have also been shown to
increase energy expenditure and
enhance fat utilization. Several studies
of various durations have provided
interesting evidence, suggesting that
energy drinks may have a role in
weight loss regimens and may provide
a potential therapeutic effect when
combined with dietary and exercise
interventions. However, additional
research is still warranted in this area.
The majority of energy drinks appear
to be well tolerated with minimal risks
associated with their use. However,
energy drinks containing ephedra
alkaloids or other b-agonists may
increase the sympathetic response
VOLUME 32 | NUMBER 1 | FEBRUARY 2010
Caffeine and Energy Drinks
(i.e., elevations in heart rate and blood
pressure) that can potentially exacer-
bate an underlying cardiovascular
problem. Interestingly, there are a num-
ber of well-controlled clinical studies
that showed that a low-dose ephedra/
caffeine combination can signiﬁcantly
alter body composition. With appro-
priate medical supervision, the use of
such energy drink combinations may
prove to be beneﬁcial. Regardless,
prudence should be used in the use
of these supplements for individuals
who are untrained, over fat, and
exercising in the heat.
Jay Hoffman is
a professor and
chair of the
Health and Exer-
cise Science at The
College of New
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VOLUME 32 | NUMBER 1 | FEBRUARY 2010
Caffeine and Energy Drinks