Four cups of Nescafé a day keeps dehydration at bay?

By Ben BOUCKLEY contact

- Last updated on GMT

Photo: Sam Howzit/Flickr
Photo: Sam Howzit/Flickr

Related tags: Coffee

UK scientists suggest they have debunked the myth that coffee causes dehydration and claim that moderate consumption provides similar hydrating qualities to water.

The study by Sophie Killer, Andrew Blannin and Asker Jeukendrup, from the University of Birmingham compares the effects of coffee consumption against water ingestion across validated hydration techniques.

Killer et al. explain that caffeine acts as a diuretic when consumed in large doses of ≥500mg, but say research suggests that low to moderate doses in ‘caffeine naïve’ individuals does not induce this effect.

“To our knowledge this is the first study to directly compare the chronic effects of coffee ingestion with water against a wide range of hydration assessment techniques,”​ they write.

“It is estimated that 1.6bn cups of coffee are consumed worldwide every day. Thus it is of interest to know whether coffee contributes to daily fluid requirement, or whether it causes low-level chronic dehydration.”

Dehydration science doesn’t stack up

Healthy adults are often advised to avoid caffeinated beverages due to dehydration risk, the authors note, but they insist such guidance is based on a “relatively small collection of caffeine studies”​ published over the past few decades (e.g. Neuhauser-Berthold et al. 1997).

“Our aim was to directly compare the effects of a moderate intake of coffee in caffeine-habituated adults against equal amounts of water across a wide range of hydration markets, including the gold standard TBW measure.”

50 male coffee drinkers (healthy non-smokers aged 18-46) habitually drinking 3-6 cups/day took part in two trials, each lasting three consecutive days.

Physical activity, food and fluid intake were controlled, and subjects drank either 4x200ml of Nescafé Original coffee (with 4mg/kg caffeine) or water, with a suitable gap left between each trial.

Total body water (TBW) was calculated before and after the trial by ingestion of deuterium oxide, while urinary and hematological hydration measures were checked daily, as was nude body mass measurement (BM).

‘Similar hydrating qualities to water’

No significant changes in TBW were found from beginning to end of either trial and between the caffeine and water trials; no differences were observed in hematological markers or in urine, osmolality or creatinine.

No significant differences in body measurement were found between the two trials.

“Our data shows no significant differences in the hydrating properties of coffee and water across a wide range of hydration indices,”​ Killer et al. write.

“These data suggest that coffee, when consumed in moderation by caffeine habituated males, provides similar hydrating qualities to water.”

But Killer et al. note the limitations of their study design, since a metabolic ward would have controlled the environment and its participants, and say a decaffeinated coffee condition would have been interesting.

Title: ‘​No Evidence of Dehydration with Moderate Daily Coffee Intake: A Counterbalanced Cross-Over Study in a Free-Living Population’

Authors: ​Killer, S.C., Blannin, A.K., Jeukendrup, A.E.

Source:PLOS One​, published online January 9 2014, doi: 10.1371/journal.pone.0084154

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1 comment

Obvious to any intelligent person!

Posted by chris aylmer,

Of course this is obvious to me. People think that because coffee(or tea) contain caffeine then they must be dehydrating. But consider for the moment the caffeine taken out of the coffee or tea as a powder, leaving the water, which is nearly all the volume. If you give the powder to an individual then it will have a small dehydrating effect depending on how much. Let us say enough to cause 15 ml to be passed out of the kidneys more than normal. Now what happens if you drink the approx 200ml water left in the original mug of coffee or tea after taking out the caffeine? It would obviously more than replace the 15ml lost and would be overall hydrating, though slightly less so than drinking just pure water in the first place. Look at it that way and you can see that tean and coffee are defi itely hydrating due to the diuretic effect of the caffeine being much less than the hydrating effect of the water.
The data must be out there for how much extra water is excreted by caffeine at a range of different doses. It is extremely unlikely that the amount of caffeine in one cup of coffee would be enough to cancel out 200ml of water drunk with it in the cup.
In any case, even in the unlikely event that coffee made with water WERE dehydrating, the feedback mechanisms in the body would soon make you thirsty enough to drink extra water.
In the tropics, I can see the logic in not drinking spirits in very hot weather, without drinking extra water....because the drinks contain very little water.

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