The safe amount of water for running

Here's the final word on how much water is safe to drink before starting running.

It’s enough to put you off your Evian, all this controversy about how much water we need, and whether having too much is potentially as harmful as not having enough... So let’s look at the evidence, and put together a watertight plan for good hydration.

It is widely accepted that the average person needs two to two and a half litres of fluid per day to allow the body to function normally, equating approximately to one millilitre for every one calorie consumed. But the notion that all fluid needs to come from water has now been questioned by some experts, who point out that at least a third of our daily fluid requirements are met by solid food, while drinks of all kinds contribute to the remaining two-thirds.

Fluid thinking for runners
According to Professor Heinz Valtin, a kidney specialist and the author of the report in the American Journal of Physiology on water consumption that sparked the controversy, there is no evidence to support the well-known ‘two litres a day’ mantra that has become such an accepted part of 21^st century healthy living. ‘I’m not suggesting we don’t need to meet certain daily fluid requirements,’ he says. ‘I’m merely questioning the notion that each and every human being should be consuming eight glasses of it a day.’

And he’s not alone in his beliefs. Professor Ron Maughan, one of the UK’s top hydration researchers agrees that drinking two litres of water, without fail, over and above other fluid intake is not necessary. Pretty much any drink at all – juice, milk, soft drinks and yes, even tea and coffee, can count towards the volume required. ‘Caffeine is a diuretic, but the fluid provided in the drink is enough to offset its diuretic effect,’ says Maughan. ‘Take 60mg of caffeine and add it to a cupful of water and milk, and you’ll likely end up more hydrated than if you hadn’t drunk it.’

He also points out that fluid comes in many forms – not just bottles and glasses. If you ate a large slice of watermelon, for example, you’d be taking a substantial amount of water on board, reducing the need to consume water in its pure form. Having said that, though, water is widely available, calorie free, it doesn’t rot your teeth or rev up your nervous system – so there’s no reason why water shouldn’t make up the bulk of your daily fluid intake. And if you’re active, you aren’t exactly going to take a glass of milk or a cappuccino with you on your Sunday run!

Effects on runners
Valtin and Maughan both agree with the consensus that regular activity or running necessitates a greater intake of fluid. Strenuous running can generate 20 times more heat than being at rest. We have to dissipate that heat somehow, to regulate and stabilise body temperature, and the body’s favoured method of losing heat is through sweating, which, of course, causes water loss.

During a high-intensity workout, such as spinning or running, you could lose 500-1000ml litre per hour – and if this fluid isn’t replenished, dehydration will set in, causing a raised heart rate, increased blood pressure, a far higher rate of perception of effort, and ultimately, a decline in performance (even a dehydration level of 2% can have a noticeable effect on your sporting prowess).

To account for fluid loss resulting from exercise, you need to think about drinking not just after training, but before and during the session, too. If you start your training session under-hydrated, you’ll be fighting a losing battle trying to compensate later. And guys be warned: research by world fitness organisation IDEA shows that men are more likely to be dehydrated at the start of a workout than women.

Your hydration strategy should begin long before you start lacing up your trainers – be aware of your food and drink intake throughout the day. Then consume 250-500ml of fluid 15-30 minutes before your running workout, depending on your tolerance of fluids, and the temperature and humidity. It doesn’t have to be all in one go...

During running exercise, aim to drink 100-200ml every 15 minutes (my home experiments equate this to roughly eight mouthfuls). If you are exercising for an hour or more, isotonic sports drinks, containing electrolytes such as salt and potassium, as well as easily ingested carbohydrate and water, are more effective at delaying fatigue and enhancing performance than plain water.

 

Don’t leave it too late to rehydrate after running
In an ideal world, you would consume the same volume of fluid after a workout that you lost through sweating, but studies show that replacing 80% of what we’ve lost is a more achievable target. You can get a good idea of this volume through weighing yourself before and after a training session to see how much weight has been lost (yes, it’s all fluid – not fat!). More often than not though, this isn’t practical, so you need to follow some general guidelines about how much to consume.

When your running session is over, regardless of its length or intensity, drink at least half a litre of fluid. After a tough session, you may want to rehydrate with a sports drink, or a carbohydrate-rich fluid such as orange juice or fruit flavoured squash. If you exercised for an hour or more, aim for a litre and keep drinking regularly for the next few hours until your urine is the colour of pale straw or lighter.

Over-hydrating before running
There’s been a lot of media coverage regarding the issue of drinking water during endurance running events, following a number of cases of ‘hyponatremia’, a potentially fatal condition in which the sodium concentration in the blood drops excessively due to too much water in the bloodstream.

The ‘drink, drink, drink’ message simply got interpreted a little too zealously and ended up causing some people to take on a lot more fluid than they needed. A study by researchers at the Memorial Hermann Healthcare Organisation in Houston, Texas found that 21 of the 5,000-odd runners in the Houston Marathon got hyponatremia. The longer the runners took to complete the race, the more at risk they were, as they tended to stop at every water station along the course. Research thus far suggests that women are more vulnerable to hyponatremia than men, probably due to their smaller body size.

To avoid being at risk of hyponatremia, try to consume isotonic drinks rather than water during endurance workouts or long runs, to prevent a drop in sodium – you could even try consuming a salty snack, such as pretzels or Ryvita. And sip, rather than glug fluids down. It’s also a good idea to drink on a schedule – say, setting your sports watch to bleep every 15 minutes, rather than drinking unconsciously and unwittingly having too much.

And finally, use your common sense when running...
If you feel thirsty, drink. If your stomach is already sloshing around with water, don’t. A report in the British Medical Journal warned that over-consumption of fluid (either water or sports drinks) before, during, or after exercise is unnecessary and can have a potentially fatal outcome, while a study by researchers at the University of Cape Town found that cyclists who were forced to replace their total sweat loss in fluid intake actually performed worse than when they drank instinctively. Like with most areas of life – you can have too much of a good thing, even when it comes to drinking water.