At a recent presentation someone told the group that caffeinated drinks dehydrate people. It is always difficult to gently correct a long held belief. I explained that caffeine causes a very small increase in urinary production at most, however, drinking cola soft drinks, tea and coffee do not cause excess urine production or dehydration. Even the more enlightened sports physicians and dietitians now tell athletes that drinking tea and coffee after training helps rehydrate the body.
Nearly a decade ago, Dr Ann Grandjean from the University of Nebraska gave people equal amounts of water and caffeinated beverages and measured their pee output for 24 hours. There was no difference between water and caffeine containing drinks. All subsequent research has shown that caffeinated drinks can be part of your fluid intake.
It is not clear who first said: “The plural of anecdote is not data”. The quote seems to suit many myths. An anecdote or observation is always worth investigating because it can lead to greater understanding. The anecdote that caffeinated drinks cause dehydration has been investigated and proven to be not correct. I might also add that “repetition without understanding slows progress”.