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Sports hydrationPublished by Bupa's health information team, May 2008. Whatever sport you are taking part in, it's important to give your body the right amount of fluids. This guide gives you information on what and how much to drink while you are exercising.
What does your body need?Your body is finely regulated, with water making up two thirds of your weight. This water accounts for 85 percent of your blood, 80 percent of your muscle, and a quarter of your bone. It's important that your body stays hydrated - keeps the right level of water - to allow vital chemical reactions to happen, and nutrients to be transported to our organs and tissues. You lose water all the time, when you urinate, sweat, or even breathe. You need to replace what you lose. When you exercise, you lose more water, so you need to drink more fluids to stay hydrated. You also need to replace minerals, sodium (salt) in particular, that you lose. During strenuous exercise, you will lose one to five grams of salt per litre of sweat. Day-to-day fluid needsThe media encourages us all to drink at least two litres (about eight glasses) of water a day, but it needn't be as strict as this. Fluids from food and other drinks count too, so instead it's best to aim to drink plenty of fluids from a varied diet and a range of drinks. It's a common belief that coffee doesn't count towards your daily fluid intake because of the diuretic (urine-producing) effect of caffeine. It's true that caffeine does have a slight diuretic effect, but in most people who drink coffee regularly, this is tiny. This is because you need to consume 300mg of caffeine for the diuretic effect to happen, which is three or four strong cups of coffee or six cups of tea. Drinking caffeinated drinks regularly leads to caffeine tolerance, so if you drink coffee every day, you would need even more than 300mg to produce a diuretic effect. You are more likely to become dehydrated if you give up your regular caffeinated drinks and forget to replace them with alternatives than if you continue to drink them. So, you should aim to drink plenty of fluids from a variety of drinks, including, water, milk, fruit juice, tea or coffee. It's a good idea to make sure that not all your fluids come from tea and coffee, and to drink more when the weather is hot and you are sweating more. Drinking while exercisingDuring strenuous exercise, the water you lose through sweating can range from half a litre to two litres per hour, so you need to replace the fluid and salts you have lost. Everyone is different; some people sweat more than others, and some lose more salt in their sweat. Because of this individual variation, it's not possible to give exact advice on how much you should drink during a session. As a general rule, you should drink 120 to 150ml of cold fluid every 10 to 15 minutes (cooler fluids because they are normally more palatable and help to lower your core body temperature). Don't wait until you feel thirsty - drink before you start, during and after exercise. Remember that you will also need to take some energy on board if you exercise for more than an hour and a half. Try a banana or dried fruit before or during a long session. The amount of extra energy you need will depend on your fitness, weight, genetics and metabolic rate. The key is to know your own body. Signs of dehydrationOne way to know whether you are drinking enough is to trust your body: if you feel thirsty you need to drink. You will feel unwell if you are dehydrated. Dehydration can give you a headache and leave you feeling tired, constipated and sick. There's a common belief that that dark urine suggests dehydration, with pale straw-coloured urine being ideal. While this may be a helpful indicator, it can be hard to judge. Drinking too much waterDrinking a lot more water than you need can lead to a dilution of the salts in the body known as hyponatraemia. Symptoms of hyponatraemia include confusion, disorientation, worsening headache, feeling sick, vomiting, impaired co-ordination and muscle cramps. If it becomes very severe, it can cause a coma, heart failure and death. It's important that the fluid you take in during exercise is around the same as that which you lose through sweat. What are the best drinks?For most people most of the time, water is fine. But if you are exercising hard, or for more than an hour, squash, diluted fruit juices, or a suitable sports drink will supply some fuel in the way of carbohydrates as well as fluid. Sports drinks are probably most relevant for serious athletes, or if you are training for a marathon. They aren't needed for the average gym work out, where you might put back the calories you have just burnt off. In addition, juices and sports drinks usually contain lots of sugar, which means they can contribute to tooth decay. Isotonic drinksThese are fluids with high levels of carbohydrates and minerals. The aim is that they contain the same concentration of dissolved carbohydrate and minerals as your blood, so they can be easily absorbed. Energy and recovery drinksEnergy drinks are particularly high in carbohydrate, to provide fuel for long-duration exercise sessions. Recovery drinks are for afterwards, to help supply the muscles with nutrients for a quick recovery. Related information |
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