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Caffeine Content of Brewed Teas

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Abstract

Caffeine is the world's most popular drug and can be found in many beverages including tea. It is a psychostimulant that is widely used to enhance alertness and improve performance. This study was conducted to determine the concentration of caffeine in 20 assorted commercial tea products. The teas were brewed under a variety of conditions including different serving sizes and steep-times. Caffeine was isolated from the teas with liquid-liquid extraction and quantitated by gas chromatography with nitrogen-phosphorus detection. Caffeine concentrations in white, green, and black teas ranged from 14 to 61 mg per serving (6 or 8 oz) with no observable trend in caffeine concentration due to the variety of tea. The decaffeinated teas contained less than 12 mg of caffeine per serving, and caffeine was not detected in the herbal tea varieties. In most instances, the 6- and 8-oz serving sizes contained similar caffeine concentrations per ounce, but the steep-time affected the caffeine concentration of the tea. These findings indicate that most brewed teas contain less caffeine per serving than brewed coffee.
Caffeine is the world’s most popular drug and can be found in
many beverages including tea. It is a psychostimulant that is
widely used to enhance alertness and improve performance. This
study was conducted to determine the concentration of caffeine in
20 assorted commercial tea products. The teas were brewed under
a variety of conditions including different serving sizes and steep-
times. Caffeine was isolated from the teas with liquid–liquid
extraction and quantitated by gas chromatography with nitrogen-
phosphorus detection. Caffeine concentrations in white, green,
and black teas ranged from 14 to 61 mg per serving (6 or 8 oz)
with no observable trend in caffeine concentration due to the
variety of tea. The decaffeinated teas contained less than 12 mg of
caffeine per serving, and caffeine was not detected in the herbal
tea varieties. In most instances, the 6- and 8-oz serving sizes
contained similar caffeine concentrations per ounce, but the steep-
time affected the caffeine concentration of the tea. These findings
indicate that most brewed teas contain less caffeine per serving
than brewed coffee.
Introduction
Caffeine is the world’s most popular drug and is found in
many beverages including tea. Although caffeine is commonly
ingested to enhance alertness and improve performance, its use
should be avoided by pregnant women, children, and persons
with cardiovascular disease and anxiety disorders. For example,
studies have demonstrated a link between caffeine ingestion
and an increased risk of miscarriage. One study supporting
these findings indicates that ingesting > 300 mg per day of caf-
feine doubles the risk of miscarriage when compared to women
whose caffeine intake is < 151 mg per day (1). Another study
shows that caffeine consumption of > 300 mg per day is asso-
ciated with lowered birth weight and smaller head circumfer-
ence (2).
As for caffeine’s effect on children, one study assessed the
physiological effects of caffeine on young boys and girls ages
7 to 9 years old. The study demonstrated that, in both boys
and girls, caffeine can produce a lower heart rate and higher
blood pressure (3). Caffeine may also affect sleep patterns in
teenagers (4).
Because of caffeine’s adverse effects, some people may choose
to control and/or reduce their caffeine intake. Caffeine is most
commonly consumed through coffee, and therefore, many
websites suggest switching to tea in order to limit daily caffeine
intake. Besides less caffeine, tea can also have health benefits
including the prevention and treatment of liver and cardio-
vascular disease, as well as producing strong bones (5–7).
Black, green, white, and many other teas (but not herbal
teas) are prepared from the leaves of the Camellia sinensis
plant. The leaves are harvested when the plant is about three
years old. The different processes for the treatment of the
leaves determine which type of tea is produced. Black and
green teas are made from young tea leaves and buds. For black
tea, the leaves are allowed to oxidize for two to three days,
whereas green tea is not allowed to oxidize at all. Instead, the
leaves are steamed and then quickly dried and stored. Like
green tea, white tea leaves are not allowed to oxidize. The dif-
ference between green and white tea is the time at which the
leaves are harvested. The leaves and buds used to make white
tea are harvested before the tea leaves are fully opened and are
still covered with thin white hairs (8).
Method
Twenty different commercial tea products, including black,
green, white, decaffeinated, and herbal, were purchased with
the following brands being represented: Bigelow, Lipton, Stash,
Tazo, Twinings, and Two Leaves and a Bud. Each tea was
brewed at 1, 3, and 5 min steep-times. All 20 varieties were
brewed in 6 oz of water, and 8 of them were also brewed in 8 oz
of water for comparison purposes.
A standardized procedure was utilized for brewing tea from
the different commercial products. To brew the teas, a beaker
was filled with the appropriate amount of deionized water—ei-
ther 6 or 8 oz. A stir bar was added to the beaker, and the
liquid was stirred and heated until lightly boiling at 90–95°C.
The beaker was then removed from the heat, and the tea bag
was held in the beaker for the allotted time while lightly stir-
ring. The tea bag was then removed, and the liquid was stirred
702
Abstract
Caffeine Content of Brewed Teas
Jenna M. Chin1, Michele L. Merves,1Bruce A. Goldberger1,*, Angela Sampson-Cone2,and Edward J. Cone2
1Department of Pathology, Immunology and Laboratory Medicine, University of Florida College of Medicine, P.O. Box 100275,
Gainesville, Florida 32610-0275 and 2ConeChem Research, LLC, 441 Fairtree Drive, Severna Park, Maryland 21146
Reproduction (photocopying) of editorial content of this journal is prohibited without publisher’s permission.
Journal of Analytical Toxicology, Vol. 32, October 2008
Technical Note
* Author to whom correspondence should be addressed. E-mail: bruce-goldberger@ufl.edu.
Journal of Analytical Toxicology, Vol. 32, October 2008
703
for 30 s. The temperature was checked, and the beaker was left
to cool for 1 h. The liquid was stirred on high for 2 min. Fi-
nally, 12 to 15 mL of the liquid was transferred to a conical
tube, labeled, and stored at 4°C.
Caffeine analysis was performed using a previously validated
method that utilized liquid–liquid extraction followed by gas
chromatography with nitrogen-phosphorus detection. The
method has been used previously to quantitate caffeine in a va-
riety of cold and hot beverages (9–11). Quantitation of caffeine
was determined with linear calibration curves (4–6 points)
that encompassed the wide range of caffeine concentrations
present in brewed teas. For example, higher caffeine concen-
trations were determined with a linear range of 25–500 mg/L,
and lower concentrations determined with a linear range of
10–100 mg/L. The limit of quantitation was 10 mg/L (or 1.8
mg/serving), and the limit of detection was 2.5 mg/L. Quality
control samples were prepared in water and interspersed
throughout the analytical batch, representing a minimum of
10% of the batch. Control sample concentrations were appro-
priate for the corresponding curve (e.g., 50, 75, and 250 mg/L).
Results and Discussion
The amount of caffeine detected in the brewed teas ranged
from none detected to 61 mg/serving. The results are detailed
in Tables I and II. Caffeine was not detected in either of the
herbal teas tested, and all of the decaffeinated teas yielded < 12
mg/serving of caffeine. The caffeinated tea varieties (black,
green, and white) yielded a caffeine content ranging from 14
to 61 mg/serving. There were no observable trends with the
different tea varieties.
Table II shows a comparison between the 6- and 8-oz serv-
ings and demonstrates that an 8-oz serving typically had a
higher caffeine content. The caffeine extraction efficiency was
calculated for the different steep-times (1, 3, and 5 min) for
both serving sizes (6 and 8 oz). The mean extraction efficiency
(%) was determined by the ratio of the caffeine concentration
in two different steep-times. In the 6-oz serving, the mean
Table I. Caffeine Content of Brewed Teas (6 oz Serving
Size) with Different Steep-Times
Steep-Time
1 min 3 min 5 min
Brand Tea Type mg/6 oz mg/6 oz mg/6 oz
Bigelow Cranberry herbal ND* ND ND
Apple Herb Tea
Tazo Passion herbal ND ND ND
Bigelow Constant decaf/black < 1.8< 1.8 1.8
Comment
Lipton Decaf decaf/black < 1.8 2.7 3.1
Stash Premium decaf/green 5.5 8.7 10
Green Decaf
Lipton Regular black 17 38 47
Stash Darjeeling Black black 14 22 27
Stash Earl Grey Black black 24 41 47
Tazo Awake black 59 59 61
Tazo Earl Grey black 40 57 59
Twinings Earl Grey black 19 22 29
Twinings English black 14 22 25
Breakfast
Twinings Irish black 17 24 30
Breakfast
Twinings Lady Grey black 14 29 30
Twinings Prince black 14 26 29
of Wales
Two Leaves and a black 19 39 49
Bud Organic Darjeeling
Tazo China Green green 23 46 41
Tips
Stash Premium Green green 16 27 36
Stash Fusion Green green/white 15 26 28
and White
Exotica China White white 23 41 47
* ND = none detected.
< 1.8 indicates that caffeine was detected, but the concentration was below the
limit of quantitation.
Table II. Caffeine Content of Brewed Teas Based on Serving Size and Steep-Time
Steep-Time
1 min 3 min 5 min
Brand Tea Type mg/6 oz mg/8 oz mg/6 oz mg/8 oz mg/6 oz mg/8 oz
Lipton Decaf decaf/black < 1.8* 2.8 2.7 3.9 3.1 4.2
Stash Premium Green Decaf decaf/green 5.5 8.6 8.7 9.2 10 11
Lipton Regular black 17 29 38 47 47 49
Stash Darjeeling Black black 14 26 22 36 27 44
Stash Earl Grey Black black 24 39 41 48 47 51
Stash Premium Green green 16 24 27 29 36 39
Stash Fusion Green and White green/white 15 30 26 35 28 36
Exotica China White white 23 32 41 37 47 34
* < 1.8 indicates that caffeine was detected, but the concentration was below the limit of quantitation.
Journal of Analytical Toxicology, Vol. 32, October 2008
704
extraction efficiency was 60% and 87% for the 1-min steep-
time compared to the 3-min steep-time and the 3-min steep-
time compared to the 5-min steep-time, respectively. For the
1-min steep-time compared to the 3-min steep-time, one tea
(Tazo Awake) was an exception with 100% extraction efficiency.
Likewise, there was an exception (Tazo China Green Tips) of
112% extraction efficiency in the 3-min steep-time compared
to the 5-min steep-time. In the 8-oz serving, the mean extrac-
tion efficiency was 78% and 89% for the 1-min steep-time
compared to the 3-min steep-time and the 3-min steep-time
compared to the 5-min steep-time, respectively. One tea (Ex-
otica China White) had an extraction efficiency of 108% for the
3-min steep-time compared to the 5-min steep-time. These
calculations indicate that the brewing conditions of steep-time
and serving size do in fact affect the caffeine content of brewed
teas. Overall, longer steep-times increase the caffeine content.
Also, when brewed in a larger serving size, one tea bag tends to
yield a larger amount of caffeine. However, when concentra-
tions per ounce are calculated, the caffeine content is typi-
cally similar.
When compared to previous studies, the caffeine concen-
tration (per oz) in brewed teas tended to be lower than in spe-
cialty coffees and energy drinks, but similar or higher than car-
bonated sodas. Furthermore, decaffeinated brewed teas tended
to have higher caffeine concentrations than brewed decaf-
feinated coffees (per oz), but lower than decaffeinated espresso
(9–11).
Although it is desirable to consumers that tea packages con-
tain information on caffeine content, only Two Leaves and a
Bud and Lipton refer to caffeine on the product label. Two
Leaves and a Bud states that Organic Darjeeling contains less
caffeine than coffee. Lipton reports concentrations of 55
mg/serving for its regular tea and 5 mg/serving for its decaf-
feinated tea, which are, in fact, consistent with the findings of
this study. Declaring the caffeine content on product labels is
important for consumers wishing to limit caffeine intake.
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Caffeine is the most widely consumed drug in the world with coffee representing a major source of intake. Despite widespread availability, various medical conditions necessitate caffeine-restricted diets. Patients on certain prescription medications are advised to discontinue caffeine intake. Such admonition has implications for certain psychiatric patients because of pharmacokinetic interactions between caffeine and certain anti-anxiety drugs. In an effort to abstain from caffeine, patients may substitute decaffeinated for caffeinated coffee. However, decaffeinated beverages are known to contain caffeine in varying amounts. The present study determined the caffeine content in a variety of decaffeinated coffee drinks. In phase 1 of the study, 10 decaffeinated samples were collected from different coffee establishments. In phase 2 of the study, Starbucks espresso decaffeinated (N=6) and Starbucks brewed decaffeinated coffee (N=6) samples were collected from the same outlet to evaluate variability of caffeine content of the same drink. The 10 decaffeinated coffee samples from different outlets contained caffeine in the range of 0-13.9 mg/16-oz serving. The caffeine content for the Starbucks espresso and the Starbucks brewed samples collected from the same outlet were 3.0-15.8 mg/shot and 12.0-13.4 mg/16-oz serving, respectively. Patients vulnerable to caffeine effects should be advised that caffeine may be present in coffees purported to be decaffeinated. Further research is warranted on the potential deleterious effects of consumption of "decaffeinated" coffee that contains caffeine on caffeine-restricted patients. Additionally, further exploration is merited for the possible physical dependence potential of low doses of caffeine such as those concentrations found in decaffeinated coffee.
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Prospective information gathered through the course of pregnancy, perinatal measurements, and retrospective data collected postnatally were used to investigate the changing patterns and effects of caffeine use of 286 women participating in the Ottawa Prenatal Prospective Study. Data were collected on maternal use of tea, coffee, caffeinated soft-drinks, chocolate bars and drinks and caffeinated medication. The volume and analysed caffeine concentration of 53 samples of coffee and tea, prepared by subjects as they usually consumed it, were used to examine the predictive potential of the women's subjective description of the beverages. Self-reports of volume and beverage strength were found to be valid predictors; the method of coffee preparation held little predictive power. An algorithm for estimating caffeine intake retrospectively over time was developed. During pregnancy most women continued to consume caffeine but usually at lower intake levels. After pregnancy, caffeine consumption tended to persist at reduced levels for several months and then returned to prepregnancy patterns. Maternal caffeine intake of more than 300 mg daily during pregnancy was associated with lowered birth weight and smaller head circumference of the infant after accounting for maternal nicotine use. No relationship was apparent between maternal caffeine use and the incidence of caesarian sections, breech births, miscarriages or premature births.
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To describe the influence of caffeine on physiological responses to exercise in young children and determine whether sex differences in these responses exist. Twenty-six healthy 7- to 9-yr-old boys and 26 healthy 7- to 9-yr-old girls volunteered to participate in a double-blind, randomized, double crossover study design. Each child randomly received both the placebo (PL) and caffeinated (5 mg x kg(-1)) drink (CAF) twice each on four separate days. Following a 1-h wash-in period and resting measures, each child rode a cycle ergometer at 25 and then 50 W for 8 min each, while HR, blood pressure (BP), and oxygen consumption (VO2) were measured. HR (bpm) was significantly (P < 0.05) lower at rest and at 25 and 50 W in CAF versus PL in both boys and girls. Diastolic BP (mm Hg) was significantly (P </= 0.05) higher at rest, 25 W in both boys and girls, and at 50 W in boys, in CAF versus PL. Systolic BP (mm Hg) was significantly (P </= 0.05) higher at rest in both boys and girls, at 25 W in boys, and at 50 W in girls. During exercise, VO2 (L x min(-1) or mL x kg(-1) x min(-1)) and RER were not different in CAF versus PL in either boys or girls. A moderate dose of caffeine (5 mg.kg) does not affect metabolism (VO2 or RER) in young children at low-moderate intensities of exercise. However, CAF causes a significantly lower HR (bpm) and higher BP (mm Hg) in both young boys and girls.