Hydration Blog

Hyponatraemia in marathon running; featured in the Telegraph - comments from Dr Jutley...

Monday, March 26, 2023

Taken from the Telegraph 26th March 2012:


The article reports the dangers of over-drinking which it claims 'can be deadlier than dehydration'.  The article is actually talking about a potentially fatal but little recognised condition called Exercise Associated Hyponatraemia (EAH) or 'water intoxication' where athletes develop low sodium levels in their blood.  This comes about from replacing sweat sodium losses with low sodium drinks or worse still water alone. With EAH water moves into the brain causing swelling. The athlete typically suffers from poor coordination, confusion, vomiting and often collapse. 

A study published only this year by two London universities showed that 12% of London Marathon runners were planning on a drinking strategy that put them at risk of EAH and that only 35% actually understood its cause and effects.

So how do you go about preventing it? Firstly you have to understand who is at risk of developing it and what conditions predispose to it. The table below shows these factors (ref: Rosner and Kirven, CJASN, 2007)
Exercise duration >4 h or slow running/exercise pace
Female gender (may be explained by lower body weight)
Low body weight
Excessive drinking (>1.5 L/h) during the event
Pre-exercise overhydration
Abundant availability of drinking fluids at the event
Nonsteroidal anti-inflammatory drugs (not all studies)
Extreme hot or cold environment
The other crucial factor (not really mentioned in the Telegraph article) is to appreciate how much sodium you are losing in every litre of sweat. 

You can either have this done at a lab using absorbent patches applied to your body which are then sent off to the lab for analysis once you saturate them with sweat. Alternatively you can have a Precision Hydration sweat analysis done at our centres http://www.myh2pro.com/sweat-testing in UK or Canada and soon in New Zealand. For those unable to take the test we can also estimate what your losses are via a quick questionnaire. 

Call us on +44(0)1273 900277 and we can take you through this over the 'phone. 

The results allow us to recommend which H2Pro Hydrate product should be right for you. From our own work and current published work the average athlete's sweat sodium loss per litre is 920 mg.  Considering that most sports drinks provide far less than this (Hi-5 Zero provides 500mg/litre; Gatorade 450mg/litre; Powerade 225mg/litre for example) you can understand why even drinking these can result in net sodium loss with the risk of developing EAH.  We avoid this problem by supplying drinks with 250, 500, 1000 and 1500 mg of sodium per litre to cater for all athletes so EAH is less of a possibility....

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