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The conventional wisdom is that people living in warm temperate climates (like the UK) need to drink 6-8 cups of water a day.
Really? Okay, so maybe those who exercise regularly drink a reasonable amount of water, but how many of the 63 million people in the country actually drink that much water?
You’d think that if tens of millions of us aren’t drinking 6-8 cups of water a day, we’d be overloading the NHS with dehydrated patients. But, um, that doesn’t seem to be happening.
A group of American and French doctors published an article showing that drinking a lot of water led to a high urine output, meaning less kidney damage from dehydration and a reduced chance of urinary infection. So far, so good, but the worrying part was that in a study that they’d done they found that the MORE tap water you drank, the higher the risk of bladder cancer!
So we'd better drink bottled water, right?
Except of course, that the article was actually sponsored by a bottled mineral water company. And all of the doctors received a payment (called an honorarium) from mineral water companies.
The truth is that we do need to be drinking 6-8 cups a day. But it doesn’t need to be bottled water, or even tap water.
You can get your 6-8 cups in coffee:
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(A real academic study in 1982 published by the British Medical Journal. not sponsored by any company, looked at the urine of medical students who had been encouraged to drink quite a lot of beer - contrary to popular belief, the beer hadn’t made them dehydrated the next day).
As long as you’re getting your water intake somehow - as juice, tea, even in food, your body will regulate itself:
if your water intake isn’t enough, you’ll get thirsty, and hopefully drink some milk, or water, or tea, or beer;
if you drink too much, you’ll just urinate more.
For most of us, in the UK, the truth is that we don’t need to worry about how much water we drink, we’ll do it anyway.
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What if you’ve been sweating it out for an hour in boxercise, bodypump or military fitness class?
Surely here, we need to keep hydrated as we’re losing water through the action of sweating.
What if you’re doing cardio, or a tough weights workout?
Dr Dan Tunstall-Pedoe is a cardiologist at St Bartholomew's Hospital in London and was the medical director of the London Marathon for it’s first 25 years. According to him, you might lose one or two pints of water during a very heavy workout at the gym through sweat - but you can replace that by drinking when you’ve finished.
Though a bottle of water at the gym seems to be a fashion requirement, it’s not actually a necessity. Sure, if you’re thirsty, have a drink - providing that it doesn’t cause you any problems doing so whilst you’re exercising. But actually, you don’t need to. You can rehydrate afterwards.
There are thousands of contradictory articles on the web advising endurance athletes (like marathon runners, triathletes and long-distance cyclists) to:
drink more to improve your performance;
drink less to avoid water intoxication which can kill you.
Let’s look at both:
Drinking water to improve race performance
It’s often claimed that the dehydration caused by not drinking enough water during endurance sports can cause a real dip in performance.
It's suggested that common symptoms of endurance athletes who are dehydrated are:
slower reaction times
worse aerobic capacity
But an Australian study published in the British Journal of Sports Medicine in September 2013 studied 4 endurance cyclists. The athletes were exercised until they’d lost 3% of their body weight through sweat.
They were hooked up with an intravenous water feed during their 7 hours of cycling, so they had no idea how much water they were being given:
enough to bring them back to 2% dehydration,
enough to bring them back to full rehydration.
The interesting thing is: there was absolutely no difference in performance between any of them.
The reality is, even in endurance exercise, drinking water doesn’t improve performance.
Drinking water to avoid dehydration during a race
If there’s no actual link between performance and drinking, there is a very slight risk of becoming dehydrated: racing for 7 hours without a drink might be daft!
Drinking properly during the pre-event training period, staying hydrated before the event (drinking, say, ½ litre 1-2 hours beforehand), and having the occasional regular top-up when thirsty during the event is enough to stay hydrated.
Most marathon runners have heard the horror stories of water intoxication ("hyponatremia") which is where someone drinks an excessive amount of water to the point where the kidneys can’t process it all. The result is a massive depletion in salt in the cells which affects the brain and can cause illness, even death. But the amount you drink needs to be excessive to even run the risk.
Common sense is what it’s all about. If you’re thirsty, have a drink. If you’re not, don’t!
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