Is There Any Point Drinking the Blue Stuff? Sometimes, and Rarely

The formulation addresses three things that prolonged exercise depletes. Water replaces what is lost as sweat. Carbohydrate supplies fuel, since the body's stored carbohydrate is limited to roughly ninety minutes of hard work and performance falls sharply once it runs low. Sodium replaces what sweat contains, helps the gut absorb water and fuel, and encourages drinking by making the solution taste of something. The concentration matters considerably, since a solution much stronger than about six to eight per cent carbohydrate empties from the stomach slowly and can cause discomfort, which is why these drinks are weaker than fruit juice or a soft drink.

The evidence supports benefit under specific conditions:

• •Continuous hard exercise lasting longer than about ninety minutes
• •Exercise in heat, where sweat losses are high
• •Repeated sessions within a day, where recovery time is short
• •Competition where small differences in performance matter
• •Situations where solid food cannot be eaten while moving
• •Not, on the evidence, for an hour in a gym or a school football match

The evidence base is large and has been examined critically, with results that complicate the marketing considerably. An investigation published by a medical journal in 2012 examined the studies behind claims made for these products and found much of the research funded by manufacturers, frequently small, frequently conducted on trained athletes under conditions unlike ordinary use, and with outcomes that did not support the general claims being made. Reviews since have confirmed benefit for prolonged endurance work and found little for shorter exercise. The advice to drink before feeling thirsty, promoted heavily for decades, has been reversed, since overdrinking during endurance events causes a dangerous dilution of blood sodium that has killed participants.

For the great majority of exercise the alternatives are cheaper and work as well. Water is sufficient for anything under about an hour, which covers nearly all recreational activity. Ordinary food eaten before and after supplies the carbohydrate and the salt, and a meal does it better than a drink. Diluted fruit juice with a pinch of salt is a workable homemade version at a fraction of the cost and is widely recommended by sports dietitians. Milk has been studied as a recovery drink and performs well, supplying protein alongside carbohydrate and fluid. And for prolonged endurance work, drinking to thirst rather than to a schedule is now the standard advice, which reverses decades of the opposite.

Two further issues have received attention from outside sports science. Dental erosion is substantial, since these drinks are acidic as well as sugary and are sipped repeatedly over long periods, which is the worst possible pattern for teeth, and dental associations have raised this specifically about young people using them casually. Consumption by children and adolescents who are not doing prolonged exercise adds sugar and calories for no benefit, and surveys find a large share of sales going to exactly that group. Marketing associating the products with elite performance is the mechanism, and several countries have restricted advertising of them to children on that basis.

Water replaces sweat, carbohydrate supplies fuel once stores run low after around ninety minutes, and sodium aids absorption and encourages drinking, with concentration kept low so the stomach empties. Benefit is supported for prolonged hard exercise and in heat, and not for shorter sessions. Much of the underlying research was manufacturer funded, the advice to drink ahead of thirst has been reversed, and dental erosion is a genuine concern.