11 replies to this topic

[Astera]

For marathon newbies, I thought I'd post an article I wrote a while back for a fitness magazine about the rare, but very real danger, of over-consuming too much fluid (hyponatraemia) during a marathon. Runners can get the 'stay hydrated' message beat into them so much, that it's possible to go to extremes, especially those bringing up the second half of the field where you're at a pace when it is easy to drink a lot.


Fluid Overload

How much water is too much during exercise? Recent health reports have highlighted a potentially dangerous condition that can be experienced by endurance athletes who over-consume water.

Being well hydrated is an important part of ensuring a sportsperson can perform at their maximum potential. Recent medical reports however have raised serious health concerns about drinking too much water during endurance sports because of the risk of a condition known as hyponatraemia. Hyponatraemia is where the sodium concentration in the blood drops to a dangerously low level. Sodium serves an important function in the body by acting as an electrolyte and helping with muscle contraction and nerve impulse transmission so the body needs to keep the concentration of this electrolyte in a fairly tight range. One condition where hyponatraemia can occur is when more water is drunk than the kidneys are able to deal with – resulting in more water being retained by the body than normal and therefore dilution of the sodium.

Hyponatraemia in healthy people is incredibly rare. Most cases occur because of medical problems where water cannot be excreted efficiently, such as in people with impaired kidney function. Some isolated case reports have also described hyponatraemia occurring in people with mental illnesses who consumed massive quantities of water in a short period of time. Hyponatraemia has also been described in people who have drunk around 3 litres of fluid over an hour in an attempt to foil drug tests. In some cases however, hyponatraemia can occur in otherwise healthy people who drink too much water during long-duration endurance exercise.

Who is at risk?
People who compete in endurance events over many hours such as marathons and ironman triathlons are especially at risk of hyponatraemia. A recent study published in 2005 in the New England Journal of Medicine measured the sodium levels of 766 runners at the finish line of the 2002 Boston Marathon. Thirteen per cent of the runners were found to have hyponatraemia and 0.6 per cent had such a low level of blood sodium that it was considered critical. The researchers also surveyed the runners about their fluid consumption during the race. Hyponatraemia was found to be associated with the following characteristics of runners:

• Drinking more than 3 litres of fluid during the race
• More than 1 kg weight gain
• Female sex
• Body mass index less than 20 kg/m2
• Drinking fluid every mile during the race
• A race time of greater than 4 hours

The risk factors for hyponatraemia in marathon runners equally apply to any activity that involve continuous strenuous activity for more than 4 hours (bushwalking or even military manoeuvres for example) when combined with excess fluid consumption. Athletes who rely heavily on water during an event and who also take on little salt to replace sodium losses through sweat are thought to be also be at risk. Athletes with a small body size (typical of many endurance sportspeople) are thought to be at even greater risk especially if they sweat a lot and are ‘over zealous’ in their drinking habits during an event.

Signs of hyponatraemia
Symptoms of hyponatraemia present as throbbing headaches, nausea, cramps, dizziness, confusion and lethargy. If the condition progresses and sodium levels fall even further, swelling of the brain can occur ultimately resulting in coma and possibly even death. Unfortunately, the initial symptoms of hyponatraemia mirror those of dehydration making the condition difficult to self-diagnose. If hyponatraemia is misdiagnosed as simply dehydration then consuming more water will only make the condition worse. Mild cases of hyponatraemia can be managed by taking extra salt combined with water restriction until most of fluid is urinated out. Standard medical treatment of hyponatraemia involves intravenous administration of a concentrated salt solution as well as using diuretics to speed water loss. While a firm diagnosis of hyponatraemia requires a blood test, something that would not be readily available at the finish line of an endurance event, some possible signs that a person may be fluid overloaded and at risk of hyponatraemia include swelling of the hands and feet or a watch or ring that has become much tighter.

How can you protect yourself?
Normally, our bodies are perfectly capable of maintaining water and sodium balance even if we drink several litres of water in a short period of time. Why hyponatraemia occurs in endurance athletes is thought to be due to muscle damage and the subsequent release of stress hormones. This metabolic response can result in reduced water excretion by the kidneys causing water to accumulate in the body and thus lowering the sodium concentration. Once the body’s water balance mechanism is impaired, drinking even a small amount of extra water can cause symptoms of hyponatraemia including swelling of the brain. Importantly though, before an event it is thought that hyponatraemia cannot occur because the body can excrete the extra water drunk so all athletes are encouraged to stay well-hydrated during their training and daily activities. Pre-event, drinking about 500 mL of fluid two hours before race time will allow the body plenty of time to remove the extra water while still ensuring the athlete is well hydrated.

It should be taken in context that death from hyponatraemia in healthy, exercising people is an extremely rare occurrence. Normally, sports people are focussed on staying well hydrated during an event as losing more than 2 per cent of body weight in fluid can impair performance. So how does an athlete walk the fine line between staying well hydrated during an endurance event while at the same time not risking becoming fluid overloaded? For events of several hours in duration, self weighing may be a good option. If a person is well hydrated at the start of an event then ‘weight gain’ during the event may mean a person is carrying too much extra fluid and should ease up on the drinks. Events such as the Boston Marathon now have scales at all drink stations in the second half of the race. As scales may not be readily available at the start and finish lines of events, athletes should consider weighing themselves before and after their more intense training sessions that mimic competition conditions. Knowing how your own body responds to activity and fluid hydration strategies will enable you to be better prepared for competition and keep your hydration status in the optimal zone.

Implication
Hyponatraemia is a potentially dangerous condition caused by excessive drinking combined with abnormal water retention during exercise. Athletes should be aware of the symptoms of hyponatraemia and aim for adequate, but not excessive, fluid intake during endurance-type sports. During the event, it is recommended that a person aims to consume about 300 to 500 mL of fluid (preferably a sports drink that contains salt) every 30 minutes. For slower, smaller athletes who are exercising in mild conditions, less fluid may be required while for well-trained athletes competing at high intensity in warm conditions more fluid may be needed.


For Reference
Almond CSD et al. Hyponatremia among runners in the Boston Marathon. New England Journal of Medicine 2005;352:1550-1556

Noakes TD. Overconsumption of fluids by athletes. British Medical Journal 2003;327:113-114

Gatorade Sports Science Center <www.gssiweb.com>

Edited by Astera, 22 September 2010 - 03:25 PM.

[mgi11a]

Astera,

Two things stood out, firstly the fact Hyponatraemia is very rare I think can be attributed to the majority of marathoners would finish closer to being dehyrated then over hydrated.

If there were 20 drink stations on the course and you took water at each one, from my experience you would be lucky to get half a 200ml cupfull in your mouth, so at best you would get 2L of fluid.

That would put you at the bottom end of the recommended fluid intake. As you say it's more likely the BOP ers who walk through the drink stations and actually drink rather then making an attempt to get water in there mouth would be most at risk.

Secondly, call me a sceptic, but as I read through I was waiting for the reference to a sports drink. Then in the last paragragh there it was, (preferably a sports drink that contains salt). Then the last line just topped it off.

Astera, on Sep 22 2010, 03:23 PM, said:

During the event, it is recommended that a person aims to consume about 300 to 500 mL of fluid (preferably a sports drink that contains salt) every 30 minutes.


Gatorade Sports Science Center <www.gssiweb.com>

Cheers

mgilla

[Bert]

mgilla

I think you are being a bit oversensitive here. The statements in the article are all supported by other material I have seen on the web and elsewhere, and the references are impecable, especially the ones to Noakes, an unimpeachable researcher in this field, and to Almond and the BMJ.

While this is undoubtably a fairly uncommon event it is still something the well-informed distance athlete should be aware of, especially with the growth of ultra events where athletes are generally travelling a bit slower for longer periods of time.

This topic has been raised here before but is one that deserves a regular reminder.

[coachrollie]

mgi11a, on Sep 23 2010, 09:19 AM, said:

Two things stood out, firstly the fact Hyponatraemia is very rare I think can be attributed to the majority of marathoners would finish closer to being dehyrated then over hydrated.

How do you 'know' that? Did you do a study, or can you refer to links?

Fewer people have died from dehydration than hyponatraemia because the symptoms of the former are limiting to further exertion, whilst the latter is most often not detected until too late, and misdiagnosed by experienced doctors who put them on a drip.

Yes you are better off drinking an electrlyte solution, but over hydration is more likely caused by too much drinking of water, than too little electrolyte.

This topic has been extensively covered by a couple of renowned sports scientists who have a blog called science in sport or something like that.

[Olmy]

coachrollie, on Sep 23 2010, 11:24 AM, said:

Yes you are better off drinking an electrlyte solution, but over hydration is more likely caused by too much drinking of water, than too little electrolyte.

This topic has been extensively covered by a couple of renowned sports scientists who have a blog called science in sport or something like that.

Here are 2 of there posts on the subject:
http://www.sportssci...ectrolytes.html
http://www.sportssci...rolytes_27.html

In the first they say:

Quote

What we have shown is that the electrolytes in sports drinks make a very tiny difference - not enough to prevent hyponatremia from developing and certainly not enough to back up the marketing claims made by the companies who tell you that you NEED the electrolytes.

(Emphasis mine)

On a related note, I also did a post in another thread (http://www.coolrunni...=0) about hydration where I looked at fluid intake. Here is a small part of that post:

Quote

If we go back to something that we learned at the start, runners in half-marathons (there is no data for full marathons) lose 1.49L per hour. Lets assume that that is the same rate for full marathons as well. Let's also assume that in a marathon or half-marathon that we do not carry our own water but rely on the drink stations on the course. For the 2010 Blackmore's Sydney Marathon there were 17 drink stations, so each one would be about 2.5km apart. Let's then look at how long it would take us between each one and how much we would have to drink depending on how fast we were running. Let's also look at two different intake strategies and how they would play out for different paces.

								Intake 1 (800mL/h)			Intake 2 (1140mL/h)
		Time Between  Amount	Actual						Actual
Pace	Stations	  To Drink  Amount  Deficit  Dehydration  Amount  Deficit  Dehydration
min/km  min		   mL		mL	  mL	   %			mL	  mL	   %
4:00	10:00		 250	   130	 1382	 2.0%		 190	 702	  1.0%
4:10	10:25		 260	   135	 1382	 2.0%		 198	 702	  1.0%
4:20	10:50		 271	   141	 2070	 3.0%		 206	 1050	 1.5%
4:30	11:15		 281	   146	 2070	 3.0%		 214	 1050	 1.5%
4:40	11:40		 292	   152	 2071	 3.0%		 222	 1051	 1.5%
4:50	12:05		 302	   157	 2071	 3.0%		 230	 1051	 1.5%
5:00	12:30		 313	   163	 2071	 3.0%		 238	 1051	 1.5%
5:10	12:55		 323	   168	 2071	 3.0%		 245	 1051	 1.5%
5:20	13:20		 333	   173	 2072	 3.0%		 253	 1052	 1.5%
5:30	13:45		 344	   179	 2072	 3.0%		 261	 1052	 1.5%
5:40	14:10		 354	   184	 2072	 3.0%		 269	 1052	 1.5%
5:50	14:35		 365	   190	 2760	 3.9%		 277	 1400	 2.0%
6:00	15:00		 375	   195	 2760	 3.9%		 285	 1400	 2.0%
6:10	15:25		 385	   200	 2761	 3.9%		 293	 1401	 2.0%
6:20	15:50		 396	   206	 2761	 3.9%		 301	 1401	 2.0%
6:30	16:15		 406	   211	 2761	 3.9%		 309	 1401	 2.0%

So we can see that to remain fully hydrated we need to be drinking between 250mL and 406mL per drink station depending on your pace (and therefore how long you will be running for). If that seems like a lot and you just want to stay at under 2% dehydration then you need to be drinking between 130mL and 309mL per station. Just remember to take conditions into account if you decide on this strategy!

[mgi11a]

Bert don't get me wrong, I think it was a great article with lots of great information for anyone new to any endurance activity, not just marathon running.
I guess the point I was try to make is that only a sports drink company would advocate you drink 2-4L of fluid preferably containing salt during a marathon.

Bert, on Sep 23 2010, 10:52 AM, said:

mgilla

I think you are being a bit oversensitive here. The statements in the article are all supported by other material I have seen on the web and elsewhere, and the references are impecable, especially the ones to Noakes, an unimpeachable researcher in this field, and to Almond and the BMJ.

While this is undoubtably a fairly uncommon event it is still something the well-informed distance athlete should be aware of, especially with the growth of ultra events where athletes are generally travelling a bit slower for longer periods of time.

This topic has been raised here before but is one that deserves a regular reminder.

coachrollie I am sure you know what your talking about when you say fewer people die from dehydration the hyponatraemia, but my point i'm trying to make is I believe there's way more people in the recovery area after a marathon suffering the effects of dehydration then that of hyponatraemia.
My comment is based purely on my observations while running and watching marathons and talking with other runners about the amount of fluid they take. Based on the 300-500ml per 30 min outlined in the article I still maintain the majority of the field would be closer to dehydration.
You don't need a study to watch people drink from a little white 200ml plastic cup and realise that even if it was full when they picked it up the chances of them getting more then half the contents in there gob is pretty slim.

coachrollie, on Sep 23 2010, 11:24 AM, said:

How do you 'know' that? Did you do a study, or can you refer to links?

Fewer people have died from dehydration than hyponatraemia because the symptoms of the former are limiting to further exertion, whilst the latter is most often not detected until too late, and misdiagnosed by experienced doctors who put them on a drip.

Yes you are better off drinking an electrlyte solution, but over hydration is more likely caused by too much drinking of water, than too little electrolyte.

This topic has been extensively covered by a couple of renowned sports scientists who have a blog called science in sport or something like that.

[undercover brother]

hi astera,
hyponatraemia has been discussed in numerous threads on CR before but its always good to have a reminder.
i won't pick through everything in your article but the last bit about 300-500mls/30mins is a bit of a red flag.
noakes et al often advocate either drinking to thirst and/or weighing as a good indication of hydration.
as soon as you mention 'blanket fluid guidelines' this excludes many variables that are in place.
i note you referenced GSSI at the end and wonder where this is from (or acsm) as these are the guidelines that noakes et al are highly critical of - blanket drinking guidelines such as those quoted above have been implicated in causing the condition you wrote the article on in order to prevent.
i vaguely remember the old (1996) gssi/acsm guidelines as 150-200mls every 15-20mins but correct me if i am wrong as i cant find them via google: regardless they are potentially dangerous and the acsm revised these in 2007.
so unfortunately by putting this in you may have undone some of the good!
but thanks for raising the topic again.
bro

Edited by undercover brother, 23 September 2010 - 03:54 PM.

[Jogger]

interesting article here:
http://www.smh.com.a...0329-1w024.html

[Perseus]

it is imperative for runners, race staff and medical personnel to understand and recognize that: 1) the scale is NOT a diagnostic tool and 2) body weight is NOT an accurate indicator of electrolyte status during an ultramarathon race. The signs and symptoms of emergent medical conditions such as dehydration/ hypovolemia, hypernatremia, hypoglycemia, heat illness and hyponatremia all overlap and can only be diagnosed through blood tests and core temperature measurement. Body weight changes should not be the sole determinant whether or not a runner is in medical “danger” but alternatively considered as adjunct information if the runner is symptomatic and onsite electrolyte analysis is unavailable.
http://www.ultrarunn...ring-a-10.shtml


A question for ultra runners in Aust. Presumably weigh-ins are common practice. Is blood testing common practice? I note all runners are now tested at Western States.

[pjay]

I have never had experience with hyponatremia although I can see it could be a problem during an ultramarathon where there would be ample opportunities to overhydrate, certainly compared to a marathon.
During the 64km Bogong to Hotham a few years ago I had copious amounts of jelly beans which I presumed gave me sufficient sodium to last the distance.  I also drank copious amounts of water and amazingly never urinated during the 12 hour journey, so I presume the water was being put to good use, as I pulled up fine at the Hotham finish line. A female entrant told me that her husband had during a previous event suffered hyponatremia, one of the symptoms presenting as a grey facial colour.  She kept filling up her hydration pack with sports drink provided at the B2H aid stations.  I thought this was going overboard a bit.

[undercover brother]

pjay, on 12 April 2012 - 10:54 AM, said:

I have never had experience with hyponatremia although I can see it could be a problem during an ultramarathon where there would be ample opportunities to overhydrate, certainly compared to a marathon..

EAH severe enough for the patient to end up in intensive care has occured in events shorter than a mararthon including a 10km event.

[walker1st]

undercover brother, on 12 April 2012 - 05:26 PM, said:

pjay, on 12 April 2012 - 10:54 AM, said:

I have never had experience with hyponatremia although I can see it could be a problem during an ultramarathon where there would be ample opportunities to overhydrate, certainly compared to a marathon..

EAH severe enough for the patient to end up in intensive care has occurred in events shorter than a marathon including a 10km event.

it happened also with no sport activity at all, there was an idiot who did some water drinking competition, died.
for running it is also important what is the salt concentration coming into the race, some could be already on the edge, with popular no salt diets system a system of drink water all the time, if the weather is hot for few days some people overdink easy and are ready for EAH at any shortish funrun.