Too Much Water Can Kill You!

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 www.aims-association.org/immda.htm.

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.