There's been quick and fierce reaction, not unexpectedly, to a recent article in the online British Medical Journal (BMJ) where GP, Dr Margaret McCartney, argues that the recommendation to drink six to eight glasses of water a day to prevent dehydration "is not only nonsense, but is thoroughly debunked nonsense."

The European Federation of Bottled Water issued this statement:

An article written by Dr Margaret McCartney, a General Practioner from Glasgow, UK, and published in the British Medical Journal published on 12th July, is dismissing the commonly accepted view that one should drink 6 to 8 glasses of water a day (or other fluids) as ‘nonsense’.

According to Mrs Mc Cartney, there would be no quality evidence to support such a recommendation.

In fact, not only is there independent scientific support in favour of a water intake of 2 liters a day from the highest EU scientific body (European Food Safety Authority - EFSA) but also it goes contrary to public health interest to discourage people from drinking water whether from bottled or from the tap.

In its Scientific Opinion on Dietary Reference Values for Water dated March 2010, EFSA stated that “Water is essential for practically all functions of the body and is particularly important for thermoregulation”, adding that “A water intake which balances losses and thereby assures adequate hydration of body tissues is essential for health and life.”

In said opinion, EFSA recommended a total water intake of 2.0 litre a day for adult women and 2.5 litre a day for adult men, under normal conditions of activity and temperature. The EFSA panel considered that solid foods will contribute 20% of that amount only.

In April 2011, EFSA recognised the role of water in the ‘maintenance of normal physical and body functions’ and ‘in the maintenance of normal thermoregulation’ and delivered a favourable opinion for the use of claims related to those benefits. In both instances, EFSA concluded that to obtain the claimed effect, at least two litres of water should be consumed per day and that such an amount can be easily consumed as part of a balanced diet.

From a public health perspective, especially taking into account growing obesity problems, water has a special role to play towards a healthy diet and therefore drinking water should be promoted.

Comment from Thomas A Sanders, Professor of Nutrition & Dietetics, King's College London:

Margaret MacCartney's article has spawned headlines in the UK national press suggesting that advice to drink 6-8 glasses of water a day is bad for you. Appropriate hydration is particularly important for the elderly and the very young and for most people it is better to obtain most fluid intake from water, whether bottled or tap water, than from other beverages (especially sugar containing and alcoholic beverages).

MacCartney focused on the more whacky claims made for water and appeared to cherry pick her references to make a story. Notable omissions were any reference to the Dietary Reference Value for Water published by the European Food Safety Authority¹ or the US Institute of Medicine review of water requirements², let alone the guidelines of the National Patient Safety Agency guidelines³.

Readers who want an unbiased view are referred to an excellent review in the British Nutrition Foundation Briefing Paper on Hydration (http://onlinelibrary.wiley.com/doi/10.1111/j.1467- 3010.2009.01795.x/full).

Six to eight glass of water represents an intake of between 900-1 200 ml per day (a small plastic cup provides 150ml water). This is not an unreasonable amount of water and is consistent with current guideline of 2 litres and 2.5 litres a day for men and women respectively after allowing for water in food and metabolic water.

The BMJ prides itself in promoting evidence based medicine. Yet this article was commissioned and did not undergo peer review. An editorial policy of publishing strong opinion pieces which are not peer-reviewed under the imprimatur of the BMJ undermines the credibility of evidence-based medicine and contributes to public confusion regard dietary advice as discussed by Cooper et al. (Public Understanding of Science 2011 doi:0963662511401782).

Competing interests: Member of Scientific Advisory Committee of the Natural Hydration Council Member of the Scientific Advisory Committee of the Global Dairy Platform Trustee and Governor of the British Nutrition Foundation.

1. EFSA Journal 2010; 8(3):1459 [48 pp.]. doi:10.2903/j.efsa.2010.1459)

2. http://iom.edu/Reports/2004/Dietary-Reference-Intakes-Water-Potassium-Sodium-Chloride-and-Sulfate.aspx

3. http://www.nrls.npsa.nhs.uk/resources/?EntryId45=59886