The idea that drinking coffee dehydrates us is a myth, scientists said last night.
They said that while we may find it hard to believe, a few cups of coffee a day is as hydrating as water.
The Birmingham University researchers called for health advice to be updated to reflect their findings.
Sports scientist Sophie Killer said that the idea that coffee dehydrates stems from research done on samples of caffeine over 80 years ago.
However, caffeine and the many other compounds in coffee interact with each other and so the 1928 study isn’t necessarily relevant to daily life.
Miss Killer said: ‘It is estimated that 1.6billion cups of coffee are consumed worldwide every day, thus it is of interest to know whether coffee contributes to the daily fluid requirement or whether it causes low-level chronic dehydration.’
To find out, the researcher asked 50 healthy men to drink either four mugs of water or coffee a day for three days and then switch.
The men ate the same food during the two parts of the study and were banned from vigorous exercise and alcohol.
Tests of blood and urine samples showed the men were just as well hydrated when they drank coffee and when they had water.
They also passed the same amount of urine, the journal PLOS ONE reports.
