Too Much Water Can Kill You!

Water: the risks, the research and the truth about overhydration

Posted: 8 July 2003
by Amby Burfoot

As she passed her coach and friends at the 15-mile mark of the 2002 Boston Marathon, Cynthia Lucero smiled and waved cheerily. It was typical behaviour for the petite woman from Ecuador. According to all who knew her, Lucero loved life, loved to help others and loved running. Seven miles later, however, something went horribly wrong.

It should have been the best of times for Lucero. The previous week she had defended her doctoral dissertation to become, in effect, Dr Cynthia Lucero. The dissertation studied the positive effect of marathon training on cancer victims and their families.

Lucero was running her first Boston Marathon. She had trained well, and eagerly anticipated the day. Things seemed to go smoothly until about the 22-mile mark, where she stopped to drink a cup of fluid. Another runner remembers hearing Lucero say that she felt dizzy and disoriented.

A few steps later, Lucero staggered briefly then fell to the pavement, unconscious. She never regained consciousness, becoming just the second runner ever to die in the Boston Marathon, and the first to die of hyponatraemia, which is caused by excess fluid consumption.

I’ve spent several months talking to experts and reading everything I could find on the subject of human hydration needs. Here’s the most interesting and useful stuff that I learnt.

Hydration And Your Health

The eight glasses myth Most adults – at least those that read the health pages of newspapers or magazines – have come to believe that they should drink eight 250ml glasses of water a day. But there’s little to no evidence supporting the eight glasses rule.

The good professor Last summer, Heinz Valtin, the Professor Emeritus of Physiology at Dartmouth Medical School, USA, published a compelling article in the Journal of the American Physiological Society. Basically, Valtin committed himself to searching out medical-scientific verification for the eight glasses rule. He couldn’t locate any.

“I have found no scientific proof that we must drink at least eight glasses of water a day,” concluded Valtin,. “The published data strongly suggest that we probably are drinking enough, and possibly even more than enough.”

Ron Maughan, Visiting External Professor of Loughborough University and the foremost researcher on hydration in the UK, agrees with Valtin. “You hear this advice from magazines, but where is it actually coming from? Not the Department of Health.” Tim Lawson, director of Science In Sport, a sports nutrition company, believes that the eight glasses rule might only apply if “you were eating dehydrated food.” He says the figure is misquoted as it fails to take into account the moisture content from food (especially fruit and vegetables) and the fluid intake from other drinks.

Of course, Valtin was researching the hydration habits of average, non-exercising Americans. Runners sweat heavily and need to drink more than non-exercisers. And the heavier and more muscular you are, the hotter the weather and the faster you run, the more you will sweat.

Beating a path to the bathroom Other experts agree with Valtin, Armstrong and Maughan that there’s no dehydration epidemic sweeping the country. If anything, we’re overhydrated. This isn’t necessarily a bad thing. It’s probably just adding to your daily mileage and calorie burn, courtesy of all those trips to the bathroom.

But there’s no evidence for the list of dehydration ills – fatigue, headache, dry skin, lack of concentration and so on – put forth by some. “Without any convincing data, I remain sceptical of all these so-called dehydration problems,” says researcher Barbara Rolls, author of Thirst, and a leading expert on hydration. “It’s a myth that’s being perpetuated. The thirst mechanism is exquisitely tuned to keep us in fluid balance.”

Maughan confirms the view that thirst is a useful mechanism, maintaining that it is simply a learned behaviour. Unlike children, who demand a can of cola as soon as they feel like it, but then only have a sip and are unable to finish the drink, adults learn to restrain the immediate impulse to drink, and to wait until they are thirsty enough to finish the entire can.

Mars and Venus When it comes to sweat rates and fluid-replacement needs, men and women come from different planets. Because men are, on average, significantly heavier than women and have more muscle mass, they sweat more than women and need to drink more. Or, to turn things around: women don’t sweat as much as men, so don’t need to drink as much. They also have a smaller blood plasma ‘tank’ than men, which is easier to overfill. Many women are new marathoners who are happy to finish in five hours or more. They reach the 20-mile mark exhausted, and think, “If I can force myself to drink more I’ll feel better.” It’s a recipe for disaster.

An overlooked truth with real-life consequences For the reasons just stated, a woman’s hydration need can be up to 30 per cent less than a man’s. This essential fact has been largely overlooked in most articles on hydration needs, and it’s particularly important for women runners, because most of the marathoners who suffer from hyponatraemia (excessive water drinking), including a number who have died from marathon-related hyponatraemia, have been women.

Hyponatraemia deaths Hyponatraemia means ‘low blood sodium’, but it’s caused by excessive fluid consumption, which lowers the concentration of sodium in the blood. As we’ve seen, in extreme cases, hyponatraemia can lead to brain seizures and death. Maughan describes the condition as “a significant danger for a small number of people.”

Last year, America’s Boston and Marine Corps Marathons had their first-ever fatalities attributed to hyponatraemia. Hyponatraemia is also beginning to appear in other endurance athletes, including ultramarathoners, Ironman triathletes and long-distance walkers. So far, there are no known cases of death from hyponatraemia in endurance events in the UK, although there have been cases associated with psychiatric illness.

New Views On Fluid Consumption

The hyponatraemia issue has forced sports and medical groups to take a new look at their hydration guidelines, and several have already adjusted their recommendations.

Marathon medicine Last autumn, the International Marathon Medical Directors Association (IMMDA) issued the first fluid-consumption guidelines from a medical organisation completely focused on runners. IMMDA, which represents some 150 major marathons on all seven continents, suggests that marathoners should consume 385-800ml of fluid per hour (you’ll need more the hotter it is, the harder you run or the heavier you are), with an absolute ceiling at 800ml. See

That’s just over half the fluid requirement proposed since 1996 by the widely-quoted ‘Exercise and Fluid Replacement’ stance of the American College of Sports Medicine, which calls for 590-1180ml per hour.

For the first time in its 107-year history, the Boston Marathon this spring provided all 20,000 runners with a fold-out pamphlet from the American Running Association and the American Medical Athletic Association. It advised runners to stay hydrated but not to over-drink, to maintain a salty diet, to favour sports drinks and to recognise warning signs.

The Gatorade Sports Science Institute has recently published one of the most comprehensive advisories on hyponatraemia, ‘Hyponatraemia in Athletes.’ It reinforces the idea that hydration is important, and that each of us sweats at a different rate, produces varying amounts of sodium in our sweat and reacts differently to heat stress.

Our Recommendations

We also believe that it’s a good time to review your hydration practices. Runners need to pay more attention to their daily fluid consumption than most people, but we don’t need to be obsessive. Given half a chance, the body will self-regulate to a normal, healthy state of fluid balance.

If you drink a lot of water and get a little overhydrated during the day, that’s okay. Your body will simply send you to the toilet. Conversely, if you can’t drink quite enough during a marathon, that’s also okay. Sit down with a sandwich and carbohydrate drink after the race, and your body will soon soak up the water it needs. Don’t rush and don’t over-drink. After a race, you’ve got plenty of time to rehydrate. Our recommendations:

  1. Drink generously, but appropriately Know yourself and your needs, and make adjustments for the weather. A runner training on holiday in Greece may need to drink more during and after a slow 10-mile run in August than during/after an all-out marathon effort on a cool spring morning.
  2. Use carbohydrate drinks Before, during and after training and races, drink carbohydrate drinks made with electrolytes. These contain the water you need, appropriate amounts of carbohydrates and small amounts of sodium, all of which are essential.
  3. Pay particular attention to post-exercise rehydration You’re likely to become dehydrated during a long, hard run, so make sure you drink enough afterwards. The sooner, the better. Same goes for food. Get your fluids, get your carbohydrates, get a little sodium, get a little protein – and you’ll be fine.
  4. Weigh yourself daily during periods of intense training If you’re losing weight, make sure it’s from fat loss, not chronic dehydration. Maughan’s recommendation is to restrict actual weight loss to one per cent of body mass. You can also check your urine colour. It should be clear or light yellow (unless you have recently taken some B vitamins, which can turn the urine bright yellow).
  5. When running long and slow – three or four hours or more – monitor your fluid consumption Be sure you’re not drinking more than you need. Also, consider running with a salty snack that you consume at the 20-mile mark. If you’re a woman, pay particular attention to these recommendations.
  6. Drink when you’re thirsty While it’s true that your thirst doesn’t kick in until you’re one to two-per cent dehydrated, there’s nothing wrong with that. Remember that your body has an “exquisitely tuned” water-balance mechanism. Use it.

Your daily drinking

The old formula – everyone needs eight 250ml glasses of water a day – is out.

It has been replaced by formulas based primarily on your gender and bodyweight.

Here are the formulas for moderately active men and women:

Male Drinking Requirement Bodyweight (lbs) x 10.36
Female Drinking Requirement Bodyweight (lbs) x 9.176

Example A 132lb women needs to drink 1211ml of water a day – 132 x 9.176 = 1211. She’ll get the rest of her daily water supply from food and metabolic processes. Runners need to drink extra to cover daily sweat losses.

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drink, hyponatraemia

Discuss this article we go again...
Posted: 28/06/2003 at 08:43

It can if you are a bad swimmer
Posted: 28/06/2003 at 08:46

Don't go swimming in the 'cut'!
Posted: 28/06/2003 at 10:56

Well - the eightx250ml is only two glasses outside my apparent resting requirement, and it says 'drink more if you run'. Duh. Doesn't seem to be a scientific equation to define 'more'.
Posted: 28/06/2003 at 10:56

Yep, seems a cut and paste job from other articles (wasn't written by FLM runner Alistair Campbell was it)?

Juliejoo, as you say I was no wiser on how much water to drink when I run having read the article.
Posted: 28/06/2003 at 15:40

I have read that if you are running on hot days and just taking on water your stomach stops absorbing it after a while and you need something isotonic or fruit juicy to break down the stomach wall again.
Something to do with the bodies self defense "I must save water " thingy or was this the basis of the article?

Posted: 28/06/2003 at 16:21

Actually - having read it now at leisure, in the sun, with a nicely rehydrating glass of wine (iced for extra water), I have to say that it was well put together, well written and really rather sensible.

What it's advocating, basically, is the classic 'moderation in all things' approach which, if everyone followed it instead of jumping on to the latest Daily Mail bandwagon, would see us all fitter, healthier and happier.

Pass the bottle, chums...

(but yes, barnsleyoldbean, I would like to know how much is 'extra').
Posted: 28/06/2003 at 17:28

there was a website that vittel did that worked out how much you would need to drink in a marathon

i cant remember what it was called, but it was advertised in the final FLM magazine this year (the one with final race instructions) - sorry but i gave mine away to somebody on one of these forums who asked if they could borrow a copy
Posted: 29/06/2003 at 00:12

Shock headline my arse.

Too much water did for Leonardo de Caprio. Do these people think we've never seen Titanic or the Poseiden Adventure?
Posted: 29/06/2003 at 17:25

Especially the night before.
Posted: 29/06/2003 at 19:36

The Brideshead Revisited star needed hospital treatment after drinking several litres - leading to a salt imbalance.

Andrews, 55, is now resting and planning to return to the stage next week for his role as Professor Higgins in the West End musical My Fair Lady.

He has missed the production at the Theatre Royal Drury Lane while being treated at a private clinic following the incident on Saturday.

It seems to have been a combination of the spell of hot weather, the fact he was drinking so much water and perspiring as well as performing so often

Penny Wesson, agent

The condition, known as hyponatraemia, is caused by the dilution of sodium in the body. It has similar symptoms to dehydration, such as headaches, nausea and cramp.

Andrews' agent, Penny Wesson, said: "It does affect you if you drink too much and perspire without replacing the salt in your system.

"He's out of the clinic now and we expect him to be back in the show in the next few days."

She added: "He's generally in very good health - you would have to be to do eight performances a week.

"It seems to have been a combination of the spell of hot weather, the fact he was drinking so much water and perspiring as well as performing so often." >


Posted: 04/07/2003 at 15:42

oops - the first part of that went missing!

Posted: 04/07/2003 at 15:43

Dangerous stuff water...

Do agree with Juliejoo about the article. I thought it was a really good piece of journalism.
Posted: 04/07/2003 at 15:53

one word

Posted: 04/07/2003 at 16:05

more beer

Posted: 04/07/2003 at 16:31

I've asked Amby Burfoot, the author (and editor of the US edition of Runner's World), if he'd like to come on the forum and answer any questions about it.

I was going to put an excerpt from it up onto the homepage, and invite questions.

Amby's away till the 14th, but he's very keen to get involved when he gets back.

Good, bad, indifferent idea?

Sean, RW
Posted: 04/07/2003 at 18:10


On your impending nuptials

Good idea, peps are fascinated by this
Posted: 04/07/2003 at 18:12

Good idea. Er... my invite hasn't arrived yet. Are your wedding arrangements being handled by the British 10k organisers?
Posted: 04/07/2003 at 18:56

waapster, thats naughty!
Posted: 04/07/2003 at 18:57


Many thanks, PH. You're all warmly invited to the wedding slide show on the site afterwards ;-)

Take it easy on Rob, Oli and Artgod while I'm away...
Posted: 06/07/2003 at 17:31

Okay guys,

Amby's back in the RW USA offices and he has agreed to check in on this thread as often as he can and answer any particular questions you may have about the article.

Obviously, because he's five hours behind us, he'll probably not be dropping in for a few hours, but feel free to post questions now for him to answer later.

So, I'll open up the floor to questions (and what DOES that mean anyway!)…

oli roberts (RW Staff Writer)
Posted: 15/07/2003 at 10:29

Okay & thanks I'll start this one off...

In your article you talk about the danger etc of over-hydration, and what had happened to those that had suffered, but so that we can be aware and avoid suffering, what are the symptoms?

Posted: 15/07/2003 at 10:38

Hi all

I guess the big question is

How much water is 'more'?

Followed by

What are the effects of
time on run
on water requirements?
Posted: 15/07/2003 at 10:38

i dont think there can be an equation because everybody's different - water requirements and more importantly electrolyte depletion varies from athlete to athlete

i read in an ironman article that salt loss through sweat can vary between individuals by a factor of 10

isn't the advice then 'drink plenty of water, but top up your electrolytes too'

or just 'drink plenty of sports drink' if you like to keep it simple

NB whoever nicked my tub of 'endurolyte' capsules at hull over the weekend please would you return them?
Posted: 15/07/2003 at 10:46

Take it easy on Rob????

Posted: 15/07/2003 at 10:49


just to second Crash Hamster's question - How much is 'more', how much is 'extra' for runners - is there a formula to take into account most of the more significant factors to get a good approximation - remember that the article was published in a running magazine so the 'at rest' formula on its own is completely useless.
Posted: 15/07/2003 at 11:33

Just reading andy colliers reference to different rates of sweat loss - it seems to be partially down to your hot weather acclimatization. Those training for at least a month in hot conditions will lose less sodium per litre than those always in cold conditions. Could this mean, for instance, that it might be an idea to pre-condition yourself for hot FLM weather by training in more clothing or going to the Med for a month?

I'd be interested to hear what Amby has to say on carb/electrolyte balance as well. Tim Noakes's "Lore of Running" book appears to suggest there may not be enough sodium in many sports drinks.
Posted: 15/07/2003 at 12:34

Another question...

Is there any benefit from what would now be termed 'overhydration' to assist with the 'excretion of toxins in the body'. For example, after a massage, or a hard workout we are often encouraged to drink lots of water.

Secondly, the article closes with the catch all 'clear or light coloured', not dark for your pee. Can we have a colour chart to determine the when light yellow becomes too dark? :-)


Posted: 15/07/2003 at 12:57

I'm a bit confused by the section that says we have an "exquisitely" tuned thirst reflex, but goes on to say that as adults, we learn to ignore it. And anyway, what about our "exquisitely" tuned bladder reflex?

I think the hyponetraemia thing is just a fad. It's the latest scare story. Picking out the only person to die of it in the history of the Boston Marathon does not make a very convincing argument. More people have damaged themselves by not drinking enough water, and then fainting away mid stride (c.f. Prague Marathon 03, British 10k 03).

David Bennett is right. We should drink more as runners, because we exercise, and not just because we sweat more as a result. And anyway, running a marathon taking in nothing but water isn't a good idea, granted, but who does do a marathon taking on nothing but water? We're runners, not ecstacy takers.

Bah. Mountains out of molehills.

Posted: 15/07/2003 at 13:25

Hello all: Here's a brief first response.

* Most importantly, yes, we're all different in all ways from speed to weight to sweat rate to electrolyte loss. Every runner has to figure out what works best for him/her.
* That said, hyponatremia is largely a female problem. They are smaller, less muscle than men, so don't need to drink nearly as much--often 30 percent less than men. Yet women--here comes a somewhat sexist but positive remark--are often more compliant than men. They have heard and believe that runners need to drink a lot, and they do. Sometimes too much, making them hyponatremic.
* Conversely, men are more prone to heatstroke, because their weight and muscle mass builds internal temperature high and fast. Of course, I hope that U.K. weather conditions are usually not hot/humid enough to lead to heatstroke.
* Big generalization that's mostly true: Hyponatremia strikes small, slow women running marathons and ultra distances. Heatstroke strikes "warrior" men who push to the max, and usually occurs in sub-marathon distances, like 5-K to 15-K, because we can run "harder" at those distances, elevating body temperature. Marathon pace is more moderate.

Run long and healthy. Amby Burfoot
Posted: 15/07/2003 at 13:40

Amby - sorry to repeat myself but what are the symptoms?
Posted: 15/07/2003 at 13:52

I agree with every point you've just made, Amby. (Cheers for posting, BTW). What I really want to ask is; how much of a problem is hyponatraemia? It seems to have spent several years as something we knew could theoretically happen, if we didn't take care of ourselves (like crossing a road without checking for cars first) to something that seems to be so dangerous that it is striking down people left, right and centre, and we're next.

I admit my back was put up by this site's homepage, with its "Water can kill you!" headline.


P.S. I did wonder why all the ecstacy deaths all those years ago, were girls.

P.P.S. A student once won a science prize for an essay about a substance that people could overdose on, and made a convincing case for banning it. The substance was di-hydrogen oxide. (See
Posted: 15/07/2003 at 13:54


Here's an overview:

Symptoms of hyponatremia are fatigue, weakness, cramping, nausea, vomiting, bloating, swelling and tightness of the hands and feet, dizziness, headache, confusion, fainting, seizures, coma, and even death. The symptoms are very similar to heat injury, and for doctors, the clue to telling these two conditions apart is the core body temperature and blood work.

How's that?

oli roberts (RW Staff Writer)
Posted: 15/07/2003 at 14:32

thank you!
Posted: 15/07/2003 at 14:33

Its that hydrogen hydroxide you all want to watch out for!
Posted: 15/07/2003 at 15:09

RE How big a threat is hyponatremia?
* Relatively small. And most cases are mild, ie, certainly not fatal. However, worst cases can be fatal, which is not true of dehydration (more below).
* At 2002 Boston Marathon, approx 13 percent of a researched runners group were hyponatremic at end. But none seriously so. Of course, there WAS a hyponatremic death at Boston in 02 and also at Marine Corps Marathon 02.
* In some Ironman Triathlons, hyponatremia has exceeded 20 percent of finishers.
* Again, most hyponatremics recover quite quickly with salt intake.
* Perspective: Hyponatremia and heatstroke are very rare, but they can kill. Dehydration is very common, but basically all it does is slow you down a little. Try to imagine Paleolithic man chasing after wild game on the high, sunny plains of East Africa 150,000 years ago. You think he didn't get dehydrated? You bet he did. But he adapted and evolved to the conditions, and got rehydrated at night when he returned to the local watering hole/pub.
Amby Burfoot
Posted: 15/07/2003 at 15:19


sorry to be so blunt earlier - I guess my point was that the formula given in the article only really works for sedentry people, there's no real indication of how much more runners need to drink. For the benefit of everyone else, I'll paste the contents of an email I received from Oli::::

The 'at rest' formula is very useful, because it's your basic daily requirement.

Once you know that, simply drink that much per day every day. Then weigh yourself before and after each run and replace further fluids as necessary.

I think this clarifies things a bit - thanks Oli
Posted: 15/07/2003 at 15:21

What's 'Amby' short for?
Posted: 15/07/2003 at 15:24

Further TRFKARR's comment:

When drinking to rehydrate post run, you need to compensate one a very individual basis based on trial and error.

The latest stuff I've found suggests a 1:1 rehydration ratio. Here's how that'll work:

Weigh yourself in kgs before and after a set distance run (say five miles. The difference (in kgs or more likely grams) is the the weight of water you have lost. Since one gram = one mililitre, this figure is also the number of mils you need to rehydrate for that distance (divide it by five and you've got your fluid loss per mile from which you can work out a ball park volume of rehydration for any run of a known distance).

Unfortunately that doesn't take into account non-constant circumstances (heat, humidity, wind, air pressure, and even for some people intensity of run etc etc).

But it's a start.

Posted: 15/07/2003 at 15:47

I think we have to remember that the reason people drink too much and suffer from hyponatraemia is more the fault of running too hard in tough conditions, not really that of water. I remember when Leanne Betts (I think that was her name) died from drinking too much water having taken an ecstacy tablet. Some idiot rave promoter said that it was therefore water that killed people, not ecstasy.

I remember reading in Arthur Lydiard's book, "Running to the Top", the suggestion that running in humid weather was better than dry weather as it helped to cool the skin. I'm still struggling to see the logic, especially as humidity tends to murder me.
Posted: 15/07/2003 at 17:00

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