Are sports drinks more effective at hydrating athletes than water?

Question

A FiveThirtyEight article, You Don’t Need Sports Drinks To Stay Hydrated challenges that sports drinks help prevent dehydration or increase exercise and performance better than water.

It claims that the studies demonstrating sports drinks are effective have been poorly done:

“As it turns out, if you apply evidence-based methods, 40 years of sports drinks research does not seemingly add up to much,”

In particular, it argues that moderate amounts of water is just as good:

One small study of cyclists and triathletes found that it didn’t really matter whether they drank plain water, a sports drink or a milk-based beverage after an hour of hard exercise. As long as they drank some liquids along with a meal, they restored their fluid levels just fine.

Is there sufficient scientific evidence that sports drinks will help with dehydration or increase performance during strenuous exercise compared to drinking the same quantity of regular water?

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Related Questions:

• Does drinking water (or Sports Drink) improve performance during sports activities?
• Can anything be 'more hydrating than water'?

Neither address the difference between the effectiveness of sports drink compared to water, so I don't consider this to be a duplicate.

Answer 1

It's difficult to find either primary research or reviews in this area whose authors haven't received grants from companies that make such sport drinks or more medically oriented rehydration solutions.

Taking the 2007 Position Stand of the American College of Sports Medicine (ACSM) to "as good as it gets" in terms of existing reviews in this area, their overall conclusion is that

During exercise, consuming beverages containing electrolytes and carbohydrates can provide benefits over water along under certain circumstances. After exercise, the goal is to replace fluid and electrolyte deficits. The speed with which rehydration is needed and the magnitude of fluid/electrolyte deficits will determine if an aggressive replacement program is merited.

And to pick some detail:

The composition of the consumed fluids can be important. The Institute of Medicine provided general guidance for composition of "sports beverages" for persons performing prolonged physical activity in hot weather (73). They recommend that these types of fluid replacement beverages might contain ~20-30 meq·L−1 sodium (chloride as the anion), ~2-5 meq·L−1 potassium and ~5-10% carbohydrate (73). The need for these different components (carbohydrate and electrolytes) will depend on the specific exercise task (e.g., intensity and duration) and weather conditions. The sodium and potassium are to help replace sweat electrolyte losses, while sodium also helps to stimulate thirst, and carbohydrate provides energy. These components also can be consumed by nonfluid sources such as gels, energy bars, and other foods.

You can already guess from this that the extra stuff in sports drinks, except for sodium (which stimulates thirst) might not be directly useful in increasing hydration but may help with other issues affecting endurance and performance, e.g. carbohydrates provide energy replacement. The Position Stand actually has a lot of material on that. So your question (focusing on hydration alone) may be too narrow in this sense.

Another issues discussed at length in the Stand (with empirical evidence mostly from marathons) is hyponatremia: drinking water (without added salt) may dilute blood sodium concentration too much in some circumstances. So again it may be too narrow to ask if you get enough water replaced.

And a 1994 paper partly derived from US Army experiences, outlined some cases when they thought more than water is needed:

carbohydrate-electrolyte replacement fluids may be necessary in some, but not all, military field situations. The greatest need for carbohydrate-electrolyte replacement fluids is experienced by soldiers who (1) lose more than 8 liters of sweat per day; (2) are not heat acclimatized (e.g., during the initial 8 days of field living); (3) are performing a prolonged, continuous exercise bout (>60 min); (4) skip meals, have meals interrupted, or encounter anorexia because of a hot environment; (5) experience a caloric deficit of >1,000 kcal per day; or (6) are ill with diarrheal disease. The fluid-electrolyte needs of soldiers are specific to the intensity, frequency, and duration of the exercise involved, as well as the environmental stress encountered. This information is not presented to imply that many different solutions are required, but rather that the best use of such fluids can be recognized with proper soldier training (i.e., when to use them) and simple instructions for field implementation. It appears that carbohydrate-electrolyte replacement fluids, like weapons, should be available to the soldier for use when needed.

The US Army might not have found such drinks to be cost-effective though. Their 2003 revised hydration guidelines (Kolka et al.) managed to reduce the experimental incidence of hyponatremia simply by reducing the water intake (and did that without an increase in dehydration).

Finally Tim Noakes has a fairly critical review (2010) of the ACSM standards (including the 2007 one) and of the older (1980s) US Army standards, particularly as it concerns the amount of fluid intake recommended, which is excessive in his view. Noakes' review doesn't cover much the add-ons provided by the sports drinks, but he is quite critical of influence that the sports drinks industry has had on research. He says for instance that hyponatremia is largely a manufactured problem by standards suggesting that athletes drink "ahead of the thirst", that is more than they feel necessary (ad libitum). He does concede that the sports drinks carbohydrates' add-on do provide some performance benefits, e.g.

[Dr. Cade's Gatorade] simple studies at the time [1971] did not show that fluid ingestion was necessary to prevent heat stroke during exercise. However, the ingestion of the carbohydrate-containing solution clearly improved performance in a 7-mile run/walk, at that time a novel finding.

Answer 2

In summary:

• In endurance exercise lasting for more than an hour, sports drinks can be beneficial over plain water because they can promote water absorption and retention, maintain physical performance and prevent water intoxication.
• The optimal content of sports drinks: sugar: 3-6 g/100 mL; sodium: 20-50 mmol/L (460-1,150 mg/L).

1) Stimulation of water absorption:

Sugar in sports drinks can increase the rate of water absorption by ~10%, but sugar content above 6% can slow down the delivery of water from the stomach into the small intestine and thus slow down the absorption (Nutrition & Metabolism, 2009 - Fig 1 - the blue line (G0) is water, G3, G6, G9 are sports drinks with diff % of glucose).

According to European Food Safety Authority (EFSA), 2011, sports drinks enhance water absorption during exercise, "which may be a beneficial physiological effect."

2) Improvement of water retention:

Sodium in sports drinks increases fluid retention in the body, which means it keeps water in your body for longer than plain water (International Journal of Sport Nutrition and Exercise Metabolism, 2017):

The purpose of this study was to examine the efficacy of water and a 50 mmol/L NaCl solution on postexercise rehydration when a standard meal was consumed during rehydration. Eight healthy participants took part in two experimental trials during which they lost 1.5 ± 0.4% of initial body mass via intermittent exercise in the heat. Participants then rehydrated over a 60-min period with water or a 50 mmol/L NaCl solution in a volume equivalent to 150% of their body mass loss during exercise. In addition, a standard meal was ingested during this time which was equivalent to 30% of participants predicted daily energy expenditure. Urine samples were collected before and after exercise and for 3 hr after rehydration. Cumulative urine volume (981 ± 458 ml and 577 ± 345 mL; p = .035) was greater, while percentage fluid retained (50 and 70%) was lower during the water compared with the NaCl trial respectively.

3) Prevention of water intoxication (dilutional hyponatremia):

Prolonged exercise (usually 4+ hours), like a marathon, during which participants drink 3+ liters of fluid with insufficient sodium content, can result in a drop of blood sodium, known as dilutional hyponatremia with brain edema, which can be life-threatening (NEJM, 2004). Sodium in sports drinks can prevent dilutional hyponatremia, but, the sodium content of some sports drinks is too low to prevent it. For example, in a 2002 Boston marathon, a 28-years-old woman has died due to hyponatremia after drinking a large amount of a sport drink during the race (Crossfit). To prevent hyponatremia, a sports drink should contain at least 20 mmol (460 mg) sodium per liter (5 mmol or 110 mg per 8 oz) (NSCA’s Guide to Sport and Exercise Nutrition).

4) Increased physical performance:

According to European Food Safety Authority (EFSA), 2011, sports drinks help to maintain endurance performance, but they do not reduce perceived effort during exercise.

In 2 small studies, drinking sports drinks was associated with increased physical performance:

a) In 7 cyclists pedaling for 2 hours in a hot environment (36 °C), Gatorade® and Powerade® preserved muscle power better (–3.1% and –3.8%) than plain water (–6%) (Applied Physiology, Nutrition and Metabolism, 2007).

b) 16 athletes were cycling for 80 minutes and then had a 10 km cycling trial. The time in a 10 km trial was better when they drank a sport drink (17.3 minutes) than when they drank water (17.8 minutes) (International Journal of Sport Nutrition and Exercise Metabolism).