Tea, a healthy beverage choice for hydration - Issue three
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Issue three
Tea, a healthy
beverage choice
for hydration
Brought to you by the
Introduction & Welcome Unilever is the world’s largest supplier of branded tea, and Lipton is one of its best known brands. Unilever has a long history in tea research - often executed in close collaboration with external tea researchers - and our findings are published in numerous papers in peer-reviewed journals. The Lipton Institute of Tea has been set up to disseminate these findings to health professionals and health media in the context of a healthy and sustainable diet and lifestyle. Its mission is to promote awareness and understanding of tea from bush to cup. The Institute is headquartered at the Lipton Tea Gardens in Kericho, Kenya - the home of Unilever’s largest tea estate - where tea is grown, plucked and processed, ready for use in Lipton and other tea brands. I hope you enjoy reading the Lipton Institute of Tea Quarterly Tea Science Overview. Additional copies can be downloaded from www.liptoninstituteoftea.org. If you have any comments on our summaries or would like to suggest articles you think we should consider for future editions, please e-mail the editorial team at: lipton.instituteoftea@unilever.com Dr Jane Rycroft, Senior Tea Based Beverages Nutrition & Health Manager, on behalf of the Lipton Institute of Tea
Tea, a healthy beverage choice for hydration Proper hydration refers to the maintenance of a constant water and mineral balance in the body. Water is the medium of numerous physiological processes, among which circulatory function, biochemical reactions, metabolism, substrate transport across cellular membranes and temperature regulation1,2. Without water, humans can survive only for days3. Proper hydration clearly is important for human health and tea can play an important role in helping to maintain hydration status. The “caffeine myth” assumes that For the general population, the rehydrating properties of tea are as good caffeinated beverages have an as those of water, making leaf tea, which consists of >99% of water and adverse effect on fluid balance, i.e. contains 0 calorie, a good beverage to fulfil daily water needs. the amount of fluid lost from the body is greater than the amount In this newsletter, we start by introducing the importance of hydration and of fluid consumed. As far as tea explore the relative contribution tea can make, explaining the caffeine is concerned, however, there is myth further. We discuss two papers that investigated the effects of caffeine sufficient evidence to exclude tea containing beverages, such as tea, on hydration status4,5. We also included from the general population advice two papers that investigated the effects of tea on the maintenance of normal to limit consumption of caffeine hydration6 and rehydration7. Taken together these papers clearly dispel the containing beverages. common “caffeine myth” as not being applicable for tea.
Adequate hydration is important for health. Water is the largest component of the human body, 1200 ml5. The World Health Organisation (WHO) representing 45-70% of total body weight8. There is a recommends 2.5 L for women and 2.9 L for men constant flux of water being lost from the lungs, skin, under average conditions and intakes of 4.5 to 5.5 L and kidneys, and water gained from food and fluids1,2. under specific conditions such as during exercise, in hot The normal daily water balance for a sedentary healthy climates or during pregnancy and lactation9. individual of 70-75 kg living in a temperate climate shows an average daily water exchange of 2550 ml. A recent review highlights the importance of proper Urine excretion usually accounts for about 1500 ml while hydration for the prevention of nutrition-related diseases the rest (1050 ml) is typically lost via sweating, respiration as kidney stones and urinary tract infections. In addition, and elimination of faeces. Food generally accounts it summarizes the consequences of dehydration, for 1000 ml of the daily water intake, metabolism for including constipation and headache and a decrease in 350 ml and drinks from all sources for the remaining physical and mental performance3.
The contribution of tea to fluid intake The caffeine myth
Thanks to its popularity and flavour which makes Caffeine (1,3,7- trimethylxanthine) is a compound
it often a preferred beverage over water, tea is an found naturally in coffee, tea, chocolate and cola.
important contributor to fluid intake in the diet10,11. Plasma levels peak around 60-90 minutes post
ingestion. The chemical structure of caffeine can be
In 2006, a guidance system for beverage found in figure 1.6
consumption was proposed by a panel of US
scientists. The panel ranked beverages from the Figure 1: Structural formula of caffeine (1,3,7- trimethylxanthine)
lowest to the highest value for hydration based on
caloric and nutrient contents and related health O
benefits and risks. Drinking water was ranked as the CH3
preferred beverage to fulfil daily fluid needs, and was H3C
N
followed directly by unsweetened tea12. The panel N
recommended consumption of unsweetened tea up to
40 oz (ca. 1 litre) per day.
N N
O
In relation to hydration, most discussion has evolved
around caffeine as an active in tea that may negatively CH3
influence water balance.
The common perception is that caffeinated
beverages have an adverse effect on fluid balance,
i.e. consumption results in a greater loss of volume
of urine than the volume of water they contain5. This
is believed to lead to dehydration and should be
avoided in situations where fluid balance is critical.
Table 1: caffeine content of tea, coffee, hot chocolate and cola in mg per serving*5
Beverage Caffeine content in mg/ serving
Serving MAFF Mc Ardle Thomas FSA Average
size (1998)13 et al (1999)14 (1994)15 (2004)16
Tea 200 ml* 40 44 45 33 41
Instant coffee 200 ml* 58 74 66.5 45 61
Filter coffee 200 ml* 93 208 411 111 206
Espresso 100 ml no data 100 no data 139 120
Hot chocolate 200 ml no data 11 no data no data 11
Cola 330 ml 23 40 54 no data 39
Energy drinks 250 ml 60 no data no data no data 60
*200 ml for MAFF, McArdle and Thomas data or 190 ml (FSA data16)
Caffeine and (de)hydration
Two papers have reviewed the role of caffeine and caffeine containing beverages on fluid balance.
Caffeine ingestion and fluid The available literature suggested consumption of caffeine containing
balance: a review, that acute ingestion of caffeine drinks on the grounds of their
R.J. Maughan & J. Griffin, J Hum in large doses (at least 250–300 diuretic effects, except when acute
Nutr Diet (2003) 16:411–420 mg, equivalent to the amount consumption of caffeine from
found in 2–3 cups of filter coffee all sources is regularly in excess
Maughan and Griffin (2003) or 5–8 cups of tea – see table 1) of 300 mg. This would be the
evaluated the available resulted in an acute diuretic action equivalent for example of 7 to 8
literature for the period January primarily in subjects deprived of servings (200ml) of tea or 2 to 3
1966-March 2002 exploring the caffeine for a period of days or servings (100ml) of espresso – see
effect of caffeine ingestion on weeks. The data also suggested table 1.
fluid balance. Subject headings that regular caffeine users become
and key words used in their habituated to the effects of caffeine, Adopting the same search terms,
search were: tea, coffee, caffeine, diminishing its acute diuretic action. we found seven new relevant
diuresis, fluid balance and water- Finally, doses of caffeine equivalent papers in Pubmed, published
electrolyte balance. to the amount normally found in between April 2002 and June
standard servings of tea, coffee and 2011. These papers concurred with
carbonated soft drinks appeared to the review of Maughan & Griffin
have no diuretic action. (2003) that caffeine ingestion
(up to 6mg/ kg body weight,
From this review, it appears equivalent to 420 mg for a 70kg
that there is no individual) does not negatively
scientific evidence influence hydration status 1,17,18,19,20.
to support More specifically, even when fluid
advice to the balance is challenged, there was
general no evidence found that tea acts
population as a diuretic when consumed by
to avoid regular tea drinkers21.
Diuretic potential of This study demonstrates that an
energy drinks, energy drink containing caffeine Based on the two papers
A. Riesenhuber, M. Boehm, increases urinary output and discussed we conclude that
M. Posch, and C. Aufricht, 31: sodium excretion over 6 hours. there is no scientific evidence
81–83, Amino Acids 2006 The dose of caffeine in the 750 to support advice to the
ml drink was 240 mg caffeine general population to avoid
Riesenhuber et al. (2006) ingested within 30 minutes. consumption of caffeine
investigated the effects of energy It is likely that the sugar-rich containing drinks on the
drinks containing caffeine (240 matrix of the test energy drink grounds of their diuretic effects,
mg), the amino acid taurine also contributed to the diuretic except when daily consumption
(3 g) or a combination of both effect. The test products of caffeine from all sources is
on urinary output and sodium contained ca. 11 g of sugar regularly in excess of 300 mg.
excretion in urine (natriuresis) in per 100 ml 22, which is very This level is reached with 2-3
12 healthy males. Recent literature high compared to commercially servings of filter coffee or 7-8
has suggested that both caffeine available isotonic rehydration cups of tea (in 1.5 L of water!
and taurine can induce diuresis drinks that contain ca. 5.5 – see table 1). As tea has a
and natriuresis in rat and man g/100 ml. Reviewing these relatively high water / caffeine
albeit acting via different cellular results in the context of tea, ratio the ‘caffeine myth’ does
mechanisms. Subjects were to see a similar diuretic effect not apply to tea. On the other
moderately dehydrated having subjects would have had to hand, some energy drinks
refrained from all drinks for 12 consume 5-6 servings of black contain very high levels of
hours before receiving the test tea in 30 minutes containing a caffeine and sugar and might
beverage. Their habitual caffeine minimum of 5 to 6 sugar cubes. therefore contribute to diuresis.
intake was moderate with subjects
only included if they consumed 4 The results of this study
or less caffeine containing drinks are in line with earlier
per day. publications, showing short
term stimulation of urine
Urinary output and natriuresis were output after acute ingestion
significantly increased by caffeine, of high caffeine doses
whereas there were no such effects (summarized by Maughan et
of taurine. al, 2003).
Tea is (re)hydrating
Two papers have investigated the effects of tea on hydration; the first paper explores the role of
tea in the maintenance of normal hydration whilst the second paper looks at the effect of water,
tea and a carbohydrate electrolyte beverage on rehydration after physical activity.
Black tea is not significantly
different from water in the
maintenance of normal
hydration in human subjects:
results from a randomized
controlled trial, Br J Nutr
(2011) C.H. Ruxton and V.A. Hart,
106: 588-595
Ruxton and Hart (2011) investigated This is one of the first studies to
the effects of tea consumption investigate the effects of tea on
on blood and urine markers of hydration status. According to
hydration of sedentary males. The the authors, previous published
twenty-one subjects consumed either data on the impact of caffeinated
four mugs (240ml each) of tea – drinks on normal hydration
equivalent to around one liter of tea were limited to three human
in total – or plain water, over a 12- experiments. These studies
hour period, in a counter-balanced however used other caffeine In the UK, both the Food
randomized controlled cross-over containing beverages (e.g. coffee Standards Agency and the
trial. The test was repeated with 6 or cola) as a test product, involved Royal College of Nursing
mugs of tea or plain water. Blood subjects that were physically currently suggest that tea and
samples were taken at regular active or were conducted at high coffee can act as diuretics
intervals following ingestion of the altitude. In the current study the and infer that water should be
drinks as well as a 24 hour urine test product was black tea with drunk alongside caffeinated
sample was collected. 20 ml milk and without sugar, a beverages to offset the
common way to prepare tea in the potential for fluid losses. This
The results showed no significant UK. Proteins from milk are known study indicates that when the
differences between the tea and to not significantly influence the average consumption is lower
water for any of the mean blood bioavailability of caffeine23 and than or similar to six mugs
or urine measures, indicating therefore the milk would not be (approx 1320 ml) of tea per
that four or six mugs of tea had a expected to counterbalance any day, no fluid losses are to
similar hydrating effect to that same potential negative effects be expected.
amount of water. of caffeine.
Effects of a carbohydrate
-electrolyte beverage
on blood viscosity after
dehydration in healthy
adults, Chin Med J (Engl)
Chang CQ, Chen YB,
Chen ZM, Zhang LT, 2010
Nov;123(22):3220-5.
Chang et al conducted a study to
assess the effectiveness of water,
(Chinese) tea and a commercial
carbohydrate electrolyte
(CE) beverage containing
carbohydrates, sodium, potassium
and calcium on rehydration after
exercise-induced dehydration.
Dehydration (2.2% of body weight) In this experiment, recovery
was induced by bicycle exercise in from high blood viscosity
a hot environment. The beverages induced by dehydration
were ingested in an amount equal was better following CE
to the body weight loss during beverage consumption
the first 20 min of the rehydration compared with water or
period, which lasted 3hours. tea. Focussing on the
comparison of tea and
Rehydration, measured by changes water only, the effects of
in blood viscosity and fluid tea and water were similar.
retention rate, was significantly Whilst a CE beverage may
higher after consumption of the CE be useful for rehydration,
beverage, when compared to tea tea does not differ from
or water. No significant differences water in its ability to support
were seen when comparing the rehydration.
effects of tea to water.
Conclusion
From this science overview the take away messages for the
effect of tea on hydration status in healthy populations are:
• Proper hydration is important for human health • S ome beverages (as energy drinks) contain
very high levels of caffeine and might therefore
• s tea consists of >99% of water and is 0 calorie,
A contribute to diuresis. These results however,
unsweetened leaf tea has been recommended as cannot be translated to tea consumption because
the second fluid choice after water to fulfil daily the caffeine content of tea is much lower than the
water needs caffeine content of energy drinks.
• T he “caffeine myth” is a widespread belief that • or the general population, the rehydrating
F
caffeinated beverages have an adverse effect on properties of tea are as good as those of water
fluid balance, i.e. consumption results in a greater
loss of volume of urine than the volume of water • ecently this was confirmed by a randomized,
R
they contain cross-over, placebo (water) controlled
trial showing that black tea contributes to
• T here is however no scientific evidence to support maintenance of normal hydration to a similar
advice to the general population to avoid extend as water.
consumption of caffeine containing drinks on
the grounds of their diuretic effects, except when • ther tea’s such as ready to drink teas and iced
O
daily consumption of caffeine from all sources is tea powder mixes are generally lower in caffeine
regularly in excess of 300 mg. and, whilst individuals need to take care to
monitor their calorie intake from sugar sweetened
• 00 mg caffeine would be the equivalent of 7 to 8
3 beverages, they can add variety and contribute to
cups (200ml) of tea. daily fluid intakes.
To conclude, adequate hydration is important for human health and taken together the papers
reviewed in this issue clearly dispel the common “caffeine myth” as not being applicable for tea.References
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2009;41:164-173.The Lipton Institute of Tea is wholly funded by Unilever.
The Lipton Institute of Tea Quarterly Tea Science
Overview is published by the Lipton Institute of Tea.
www.liptoninstituteoftea.org
http://twitter.com/liptoninstitute
lipton.instituteoftea@unilever.com
Published January 2012
All information correct at time of going to press
For health care professionals only
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