Do we need to drink 8 glasses of water a day?

A Scottish GP, Margaret McCarthney, wrote a feature article in the BMJ last week that the common recommendation to drink 6 to 8 glasses of water a day is "debunked nonsense", as a result, hundreds of comments, some agreeing, many disagreeing, were sent to the BMJ and other media.

The GP argued that there is no high quality evidence to support the recommendation and that too much water can lead to hyponatremia and other problems. She said that the "Hydration for Health" initiative, sponsored by Danone, maker of bottled water Volvic and Evian, has vested interests to re-inforce the myth. Dr McCarthney argued that reports that drinking more water can improve concentration and mental performance in kids have lacked evidence and that Hydration for Health has oversold the benefits of drinking more water without clear evidence to support it. "We should just say no", she said.

An expert noted that there is well established literature on the negative effects of dehydration on mental skills in adults and children. Another said that the author failed to mention an important US report(2004) that reviewed all studies.

Dr McCartheny argued that her article was to examine the evidence of the benefits that Danone claimed via "Hydration for Health" and was not a systematic review on the subject and she did not imply that it is dangerous for children to drink 6-8 glasses of water a day.

Source: Waterlogged? BMJ 2011; 343:d4280 doi: 10.1136/bmj.d4280 (Published 12 July 2011) , full text via Athens