Food is the Forgotten Medicine (c)
Water is the largest single constitute of the human body and is essential for cellular homeostasis and life.
Despite this, there is no agreed recommended daily intake for adults in the UK.
Part of the problem is that we all vary so differently as to how much water we can excrete and hydration can be maintained over a wide range of water intakes. Not surprising when you consider all the different variables at play – metabolic rate, body mass, size…then there’s the environmental conditions – humidity, wind, solar load, clothing, heat acclimatisation status, fitness levels, diet etc etc…
However, the maximum amount anyone should drink is well understood as the kidney’s maximal excretion rate is 0.7 – 1.0L per hour. Acute water toxicity has been reported at above these rates with tragic consequences.
“A 28-year-old California woman died after competing in a radio station’s on-air water-drinking contest. After downing some 6ltrs of water in 3 hours in the “Hold Your Wee for a Wii” (Nintendo game console) contest, Jennifer Strange vomited, went home with a splitting headache, and died from so-called water intoxication.” — Scientific American
With the obligatory health warning out the way… lets look at the little water intake recommendations there are…
The US survey recommends Adequate Intake (AI) Fluids (drinking water and beverages) provided 3.0 L and 2.2 L per day for men and women, respectively (another 20% of fluid on top comes from food).
Our NHS suggests a lot less – women 1.6L and men 2L per day – and references the European Food Safety Authority for this statistic. http://www.efsa.europa.eu/en/efsajournal/pub/1459.htm
Hmmm…i smell a rat! …1.6L is the same as the well-trumpeted advice of 8 glasses (200ml) of water…does anybody know the mythical research that came up with 8 glasses per day?!
…even more bizarrely, if you take the time to check (nobody but yours truly is that sad!) the European Food Safety Authority doesn’t actually advise 1.6 or 2L of water per day…but rather 2L and 2.5L for women and men respectively (2010) – which is a lot closer to the US survey of 2.2L and 3.0L for women and men.
My own experience tells me that recommended intakes for anything (RDA’s, RDI, AI) tend to be on the very conservative side – the aim is always the minimum dose that will prevent sickness. However, the minimum dose to prevent sickness is unlikely to be the same dose for optimum health…especially for those training hard.
The formula that works for me and my clients is 30-35ml of water per KG of bodyweight.
So for me – at 80kg – i’m aiming for 2.8L per day – with a good deal more if i’m training hard (around 4ltrs)