Tea versus water

“Drinking four to six mugs of tea a day is as good for keeping you hydrated as a litre of water,” reported the Daily Mail. It said the finding disproves “the idea that regular tea drinking can dehydrate the body because of its caffeine content”.

The newspaper report is of a trial of 21 volunteers, which compared hydration levels in people drinking four mugs of tea with their levels when drinking the same amount of water on two different days. The study, sponsored by the UK Tea Advisory Panel, which in turn is sponsored by the UK tea industry, found no difference in hydration levels when tea or water was drunk.

It is perhaps unsurprising that in terms of hydration there was little difference in the two experimental conditions. The important question is whether caffeine is a diuretic, but this study did not measure the caffeine in the tea. It also cannot comment on which of the two drinks – tea or water – are healthier overall.

Tea

The Tea Advisory Panel’s website reports that this is a randomised crossover trial. There is limited further detail provided about the study’s methods. Twenty-one healthy males aged 20 to 55 years old were enrolled. The study excluded people taking medication that may impact on markers of hydration, those who may be allergic to test ingredients, smokers and those with excessive caffeine intake (more than 10 cups of coffee per day). The same group of men were assessed during a 24-hour period of tea drinking, then a 24-hour period of water drinking. Measures of hydration were compared between the two experimental conditions.

This is a small study and it has not been possible to appraise the research fully given the limited details presented in the Tea Advisory Panels website. It suggests that, at least in terms of hydration, consumption of equivalent amounts of water and tea over the course of a day deliver the same level of hydration.

The report says that the level of caffeine in the tea was not measured, so it is not possible to say whether all participants received the same dose or what the exact dose was.

The authors say they used black, i.e. regular tea. The results may not apply to other teas.

It is possible that the diuretic effect of tea is evident at higher doses of caffeine. The researchers aim to conduct further studies of people drinking more tea. If these are conducted, it seems reasonable to include women in the trial too.

The finding that water and moderate tea consumption are equally hydrating are perhaps unsurprising.

The important question here is whether caffeine is a diuretic. However, this study did not measure the caffeine in the tea that was given. It also cannot comment on which of the two drinks – tea or water – is healthier overall.