It is often claimed that caffeinated drinks, such as tea, have an adverse effect on hydration. While studies on caffeine pills have produced inconsistent results(Reference Ruxton1), those on caffeinated drinks, at caffeine intakes of 114–420 mg, have found no significant impact on hydration(Reference Grandjean, Reimers and Bannick2, Reference Fiala, Casa and Roti3). However, there have been no randomised controlled trials on tea, as consumed. The present trial aimed to assess the impact of 4×240 ml mugs of black, i.e. regular, tea on blood and urine measures of hydration.
Following informed consent, 21 healthy men, who had abstained from caffeine and intense exercise for 10 h, took part in a randomised, cross-over trial. Black tea with semi-skimmed milk was made, using a standardised protocol, and was drunk at fixed, regular intervals over a 10-h period. Water, at an equivalent volume and temperature, was used as a control. Bloods were taken at baseline and on 5 other occasions over 12 h. Changes in individual blood parameters between baseline and 12 h (time 12 minus time 0), for the 16 subjects whose results were available, are shown below:
Urine was collected over 24 h and analysed. Comparisons in 24 h urine parameters between the water control and tea condition for the same 16 subjects are presented below:
No significant differences were found between tea and water for any of the blood or urine parameters. This suggests that tea is equally hydrating to water at an intake of 4 mugs per d, equivalent to a daily caffeine intake of about 200 mg.
The research was funded by the Tea Advisory Panel.
