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Q: How much water does my 12-year-old son need to drink during a tennis game so he doesn’t become dehydrated, especially in hot weather? Should he use a sports drink instead of water?

Water is critical to athletic performance. It regulates body temperature, allows muscles to contract and helps the bloodstream deliver oxygen to body tissues.

In kids, losing 1 per cent of their body weight due to dehydration has been shown to have detrimental effects on performance. (In adults, performance can suffer at a loss of 2 per cent of their body weight.)

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The key to preventing dehydration during sports is knowing how much – and what – to drink before, during and after exercise. And when exercising in hot weather, extra careful monitoring of fluid intake is crucial.

Signs of dehydration

While dehydration can drain physical and mental performance on the tennis court or soccer field, there are more serious, even life-threatening, consequences.

Not drinking enough fluids when exercising vigorously and sweating heavily can cause a heat injury, ranging from mild heat cramps to heat exhaustion to heatstroke, a medical emergency.

Symptoms of mild to moderate dehydration include fatigue, loss of appetite, flushed skin, light-headedness, muscle cramps, headache and dry mouth.

Warning signs of severe dehydration include very dry skin, dizziness, rapid heartbeat and breathing, confusion, irritability and fainting.

How much water before, during and after?

Practicing good hydration during the day is essential to help reduce the risk of dehydration during exercise. Research from the University of Carolina found that 50 to 75 per cent of young athletes were already dehydrated before practice and competition.

According to the U.S.-based Institute of Medicine, boys between the ages of 9 to 13 should drink 1.8 litres (about 8 cups) of water each day (1.6 litres for girls). Teenage males and females require 2.6 and 1.8 litres of water a day, respectively. Adults are advised to drink 2.2 litres (women) and 3 litres (men) daily.

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All beverages – with the exception of alcoholic ones which cause your body to lose water – count towards your daily water intake (e.g., plain water, milk, juice, tea and coffee).

During exercise, the American Academy of Pediatrics recommends 100 to 250 ml every 20 minutes for 9 to 12-year-olds and up to 1 to 1.5 litres for teenagers to minimize water loss through sweat and prevent overdrinking. That’s provided kids are well hydrated before starting exercise.

Adults should drink 125 to 175 ml of water every 10 to 15 minutes of exercise.

Weighing yourself before and after exercise can give you more information about your rehydration needs.

For every pound lost during activity, drink 500 to 750 ml of water. Drink water with your post-workout snacks and meals to achieve this.

Are sports drinks appropriate?

Most physically active children (and adults) don’t need sports drinks such as Gatorade or Powerade. These drinks can, however, benefit kids who exercise for one hour or longer, participate in same-day sessions of strenuous exercise or sports, or who exercise vigorously in hot weather.

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Along with fluid, sports drinks deliver electrolytes (e.g., sodium, potassium, chloride) that get lost in sweat. Electrolytes help regulate nerve and muscle function; getting too little can hinder performance, cause cramping and dizziness and, potentially, lead to heat injury.

The main electrolyte lost during prolonged exercise is sodium. That’s why the American Academy of Pediatrics recommends choosing a sports drink that contains more sodium than other minerals.

Many sports drinks also contain 6 to 9 per cent carbohydrate in the form of sugar to provide energy for working muscles.

Numerous studies have shown that sports drinks delay fatigue, enhance performance and speed recovery in athletes.

For kids who engage in routine exercise, though, plain water will do just fine. Guzzling sports drinks will increase a child’s intake of sodium and refined sugar; prolonged intake has been linked to tooth decay and erosion.

What about coconut water?

For people who engage in long bouts of vigorous exercise that produces a lot of sweating, coconut water isn’t a suitable sports drink.

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While coconut water is very high in the electrolyte potassium, it’s lower in sodium than regular sports drinks. As such, coconut water alone can’t replace the sodium that’s lost during strenuous exercise.

Leslie Beck, a Toronto-based private practice dietitian, is Director of Food and Nutrition at Medcan.

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