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Tea and hydration
For millions of people, drinking tea plays a significant role in maintaining fluid balance. Indeed, approximately 40% of the nation’s fluid intake will come from tea.
Fluid balance is crucial for a healthy body function. In addition, it is a major component of the body and requires continual replenishment. Water regulates body temperature, transports nutrients and oxygen in the blood, allows excretion of waste products in the urine and faeces and lubricates the body tissues including the joints and eyes.
Most adults need about 6-8 cups (1.2 litres) of fluid daily. However, the Tea Council’s Healthy Drinks Survey found that a third of all adults in the UK are not meeting their daily fluid requirements. A cup of tea is 99.5% water. So, four cups of tea each day can significantly contribute to the body’s fluid balance.
It is a common misconception that tea should be avoided as a means of fluid replacement because the caffeine in it will cause a diuretic effect resulting in a net loss of fluid and dehydration.
The misconception that caffeine-containing drinks cause diuresis originates from research that looked at large ‘experimental’ doses of caffeine in a laboratory, not ‘real life’ consumption of tea. While there is evidence from such studies that single, high doses of caffeine may cause a diuretic effect, there is no evidence that the normal use of tea in real life - where the caffeine would be consumed with 200-250ml of fluid – would cause diuresis.
A review of studies on the effects of caffeine ingestion and fluid balance2 distinguished between studies using large experimental doses of caffeine and those investigating real life consumption. This review came to three main conclusions:
A very recent review3 of double-blind, placebo-controlled studies published over the past 15 years looking at the effect of caffeine on mood, cognitive function, performance and hydration concluded that caffeine intakes up to 400 mg per day did not produce dehydration, even in subjects undergoing exercise testing. The reviewer also found that the range of caffeine intake that could maximise benefit and minimise risk in relation to mood, cognitive function, performance and hydration is 38 to 400 mg per day, equating to 1 to 8 cups of tea, or 0.3 to 4 cups of brewed coffee per day. Current levels of caffeine intake in the UK fall well within this range, suggesting that risk, for example from dehydration, is likely.
A cup of tea normally contains less caffeine than a cup of coffee. A cup of tea contains about a third of the caffeine in an average cup of filtered coffee (and proportionately much less compared to espresso).
These conclusions were confirmed in a later study4 that compared regular tea drinkers with non- tea drinkers in a study of fluid balance at Everest Base Camp. The risk of dehydration at such high altitudes is considerable, but even when tea was drunk in this study, it did not produce diuresis in the participants.
Tea is hydrating
It is vital to drink enough fluid, but there is perception that fluid requirements have to be met by water alone. Eight cups of water a day is often cited as the recommended daily intake for fluid. Advising people to abstain from other drinks, including tea, because of the misconception around caffeine and dehydration, could actually lead to dehydration because of a failure to make up the difference with other drinks.
A cup of tea is made up mostly of water and is an excellent means of hydration. The importance of consuming water as the sole means of hydration has been overemphasised. People may be forcing themselves to drink 8 glasses of water a day, not realising that tea, like water, is hydrating and can contribute to daily fluid intake.
The amount of caffeine in tea is relatively low and up to six cups of tea (300mg of caffeine) can be drunk daily with no danger of causing any diuretic effect.
1. British Dietetic Association. Hydration. Fluid facts. http://www.bda.uk.com.
2. Maughan RJ, Griffin J. Caffeine ingestion and fluid balance: a review. Journal of Human Nutrition and Dietetics 2003;16(6):411-420.
3. Ruxton CHS. The impact of caffeine on mood, cognitive function, performance and hydration: a review of benefits and risks. Nutrition Bulletin 2008;33(1):15-25.
4. Scott D, Rycroft JA, Aspen J, Chapman C, Brown B. The effect of drinking tea at high altitude on hydration status and mood. Eur J Appl Physiol 2004;91(4):493-8.
The idea that tea contains as much caffeine as coffee is erroneous. A cup of tea contains about a third of the caffeine in an average cup of filtered coffee and proportionately much less compared to... Learn more