Are We Drinking Too Much?

What happens when you over-hydrate.


Words Michele Tan

A common sight during large race events, pre-race, is of athletes clutching water bottles and chugging large quantities of water. This precedes joining the line for the over- subscribed portaloos.

Some elect to run gripping their water bottles as if they are embarking on a desert crossing, disregarding the fact that urban distance races provide water stations at very short intervals throughout the race. Significantly, the elite runners don’t do that.

This article may challenge some widely held beliefs but if you have doubts do check out *Tim Noakes’ book. It is state of the art science on a subject he has studied for many years and his views are endorsed by IMMDA.

What is wrong with drinking as much as you can before, during and after the race?

The problem with this practice is that your body can become literally waterlogged.  In runners or triathletes this can lead to a medical condition called Exercise Associated Hyponatremia (EAH) which means excess water in the system relative to sodium levels. If drinking persists, the next stage can be Exercise Associated Hyponatremic Encephalopathy (EAHE) which is a medical emergency.

What are the dangers of over-drinking?

Hyponatremia is a condition where sodium levels in your body are too low relative to blood volume.  The sodium in your body helps to regulate the amount of water inside and outside cells. Too much water can result in waterlogging which may lead to swelling of the brain (EAHE) with potentially fatal results, however heavily you sweat.

How much should I drink?

Noakes’ and the IMMDA guideline is 400-800ml/hour. No more. Less is not a problem if you don’t feel thirsty. Some of the fastest marathons have been won by athletes who took no drinks at all for the entire race. We are not advocating that in Singapore’s climate, but be aware that problems can arise from over- as well as under- drinking.

Does one size fit all?

No. Faster runners and slower runners are different. Slower runners, because of the longer time they are out on the road, and because it is easier to drink at slower running speeds, are at greater risk of over-hydrating if they feel compelled to drink at every water point.

The advice to drink only when thirsty is best. If you are out in hot conditions for more than four hours you will get thirsty and need to drink. It is better to go with how your body feels (i.e. thirsty or not thirsty) than ‘drinking by numbers’ so to speak.

How serious is risk of dehydration? 

Is it dangerous? Transient dehydration (four to eight hours) is no problem. We are not talking here about getting lost in the desert for days.

Dehydration has one symptom: Thirst. The weight loss associated with moderate dehydration during the latter stages of a race confers an advantage. Winners of races are shown to be the most dehydrated (lost the most weight in the course of the race).

The lighter body weight in the closing stages of a race will be helpful in maintaining pace when tired. Once the race is over, rehydration can begin and a post-race meal will replace all the sodium lost during the event.

Is heat exhaustion or heat stroke caused by dehydration?

No. They may be associated and found in the same individual in particular circumstances but one does not cause the other. The highest body temperatures have been found in athletes at the end of 5km to 15km races.

No one gets seriously dehydrated in a 5km race. The higher recorded temperatures are related to the higher work rate at these distances. In 21km - 42km and beyond (Ultra races), the work rate does not result in such high temperatures.

The issue to be aware of though, is that the longer the distance and the slower the pace, and the more opportunity there is to over-drink.

Are commercially produced sports drinks the answer?

Not if you are thinking that their electrolyte content is going to be of much help. The actual sodium content in them is quite low.

Chugging large quantities before, during or after the race can lead to hyponatremia just as if you were drinking too much water. The water volume in these sports drinks will over-hydrate you just as if it were plain water.

Can I make my own sports drink?

Yes. Medically approved hydration salts can be purchased in sachets at pharmacies and can be mixed in your own water bottle together with your glucose of choice.

If you make up a solution that is slightly too salty to be palatable at rest it will probably be very palatable when you are well into your race. I would recommend a 250ml bottle as it is easier to carry your fairly concentrated mixture (maybe 3 sachets in 250ml of water) and then use the water stations to wash it down with a sip of plain water.

How do I know if I am over-hydrated, or water logged?

The single most reliable measure of over-hydration is weight gain. If, at the finish of the race, you weigh more than 2% of your starting body weight you are over hydrated. If your watch strap or race bracelet feels tight, you feel bloated and weak, you have probably been drinking too much and you need to stop drinking.

Aside from the medical risks of over-hydrating, Noakes found that runners with as little as approximately 1% increase in weight gain due to excess fluid intake suffered impaired performances. So over-drinking even before the event will have the same result: you will start the race feeling heavy (which you will be) and bloated.

What is wrong with athletes who collapse at the end of a race?

There may be several medical reasons but the most common is Exercise Associated Postural Hypotension (EAPH). When you stop running blood pools in legs depriving the brain of blood, oxygen and glucose. The condition (if it is EAPH) is fixed by lying down and raising legs above head/heart.

Cool down jogging also helps to avoid this condition occurring. This is one of the reasons we do a cool down jog. Of course many athletes don’t feel like doing that when they have just crossed the line after a 21km or 42km race. But even walking around is better that standing still.

Note that this has nothing to do with dehydration or heatstroke or hyponatremia.

What is the best drinking protocol in a nutshell?

400-800ml/hr, only as thirst dictates. In other words this is a maximum recommended not a required minimum.

Pre-race: stop drinking once you pass clear urine. However hot the conditions are there is absolutely nothing to be gained by continuing to drink, as you are not a camel and cannot store water for use at a future time. Further drinking can only result in time lost searching for toilets or start you on the risky path to hyponatremia.


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