The research, commissioned by the Tea Advisory Panel (TAP), has found that drinking up to six mugs of tea a day is just as hydrating as the equivalent volume of plain water – with no negative health effects.
The findings, set to be published on the 29th March in the British Journal of Nutrition, shatter the common – but hugely flawed – notion that regular tea drinking can dehydrate the body, depriving it of vital fluid necessary for optimal mental and physical health. The misconception stems from some previous research on caffeine pills which, at high doses, can increase the frequency of urination. Tea is a moderate source of caffeine, containing around 50mg per mug.
Until now there has been little conclusive evidence whether or not caffeine in drinks, such as tea, could provoke excessive urination and dehydration. However the latest study – a randomised controlled trial - has finally demonstrated that, as an everyday drink, tea has the same beneficial hydrating properties as water.
In the UK-based study, a total of 21 volunteers drank either four 240ml mugs of tea over a 12-hour period – equivalent to just under one litre of tea in total – or a similar amount of plain, boiled water served warm. The tea was prepared in a standardised way from tea bags and included 20 ml of semi-skimmed milk but no sugar. Four cups of tea was chosen because this is slightly above the average daily tea intake in the UK of 540ml or 2.4 cups. However the test was also repeated with subjects drinking six cups of tea or plain water – equivalent to nearly 1.5 litres of fluid – in order to investigate the impact of higher tea intakes.
Commenting on this latest published study, independent dietitian and nutrition advisor to the Tea Advisory Panel, Dr Carrie Ruxton notes: “Tea and water were found to offer similar hydrating properties at intakes of up to six cups, making tea an excellent way to maintain healthy fluid levels. In addition, tea is a rich source of flavonoids, which have been associated with a reduced risk of heart disease and stroke. Thus, tea could be considered a healthy choice of beverage. Not only is a mug of tea refreshing and delicious, it can be an important part of maintaining proper hydration.”
In the study, the all-male volunteer group had an average age of 36 years and none had habitually high caffeine intakes. The study was a randomised cross-over trial so each male was given both tea and water on separate study days with a wash-out period in between. A controlled diet was given during the test days and there was a ban on vigorous exercise, caffeinated products and alcohol for 14 hours prior to each test day.
Blood samples were taken before drink consumption and then at 1, 2, 4, 8 and 12 hours during the test days to check levels of electrolytes, total protein, urea, creatinine and osmolality – all recognised markers of body hydration. Urine was collected over a 24 hour period to gauge total volume and to check levels of creatinine, osmolality and electrolyte concentration – again common markers of hydration. Following a detailed analysis of all of the results by a qualified statistician, no significant differences were found in terms of hydration levels between drinking tea and water. Drinking four or six cups of tea over one day was found to be equally hydrating to drinking the same level of water.
While previous research on caffeine pills have produced inconsistent results due to differences in caffeine levels, the small amount of research on caffeinated drinks has found no significant impact on hydration levels.
Dr Ruxton says: “It’s a common misconception that drinking tea can increase the risk of dehydration because of its caffeine content, but this study proves that there is absolutely no truth in it. No statistical differences were found between regular tea consumption and water when a wide range of blood and urine markers for hydration were tested among the volunteers. In addition, urine volume was similar after tea or water, confirming that we do not urinate more after drinking tea.”
In particular Dr Ruxton is calling for public health guidelines to be changed to reflect the latest findings, so that tea is recognised for its hydrating properties. She says: “Wrong advice that identifies tea as dehydrating could be misleading and serve to drive consumption towards less healthy drinks. Given the findings of the present trial that consumption of tea at either four or six cups had no adverse effects on hydration and bearing in mind that tea is one of the top drinks to meet daily water needs, it could be argued that public health advise relating to caffeinated drinks should be revised.”
Health expert Dr Catherine Hood, a member of the Tea Advisory Panel, adds: “It’s vital that everyone keeps their fluid levels topped up to avoid dehydration - proper hydration is key to good mental and physical health. Tea drinkers can be reassured that their favourite cuppa does count towards their fluid intake without the risk of dehydration. A growing number of scientific studies have demonstrated just how useful tea can be in keeping the body in good condition thanks to its high polyphenol content, which gives tea its characteristic colour. Tea polyphenols not only have antioxidant effects but also help maintain normal vascular function, which could impact favourably on blood pressure. This may explain why many studies have linked regular tea consumption with a lower risk of heart disease and stroke.”
Dr Hood adds: “There has been some debate over whether tea retains its healthy properties if drunk with milk, but again studies have shown that the positive effects of tea are just the same whether or not milk is used.
“The findings of this latest research agree with previous studies on caffeine pills and other caffeinated drinks which demonstrated no adverse effects on hydration when a moderate caffeine intake (114-420mg/d) is consumed. Caffeine levels measured in the current study indicated that the participants were consuming either 168mg or 252mg of caffeine per day from the tea drinks provided”.
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The Tea Advisory Panel: The Tea Advisory Panel is supported by an unrestricted educational grant from the UK TEA COUNCIL, the trade association for the UK tea industry. The Panel has been created to provide media with impartial information regarding the health benefits of tea. Panel members include nutritionists; dieticians and doctors. For further information please call 0207 7052 8989.
Notes to editors:
The trial was a single centre, single blind, randomised, crossover study to assess the effects on body hydration of black leaf tea. The independent study was undertaken by scientists at Reading Scientific Services Limited, a contract research organisation, with funding by the UK Tea Council Limited.
 Popkin; 2009
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