Are electrolyte drinks better than water?

At rest

In a trial of 72 men, each drank 1 litre of a drink in 30 minutes, and their urine was collected for 4 hours.^[2]

• After still water, they passed 1,337 g of urine.^[2]
• After an oral rehydration solution, they passed 1,038 g, and after full-fat or skimmed milk about 1,050 g.^[2]
• Cola, tea, coffee, lager, orange juice, sparkling water and a sports drink did not differ from water.^[2]

In another trial of 19 young adults at rest, electrolytes alone did not keep more fluid than water every time. A drink with carbohydrate and electrolytes kept about 15% more fluid than water after 2 hours. One author had consulted for Coca-Cola.^[4]

After exercise

In a trial of 26 athletes, each trained for 90 minutes without drinking and lost 2.6% of body weight. They then drank a volume equal to the loss.^[1]

• Water: 58.1% of the fluid stayed in the body after 3.5 hours.^[1]
• Sports drink (18 mmol of sodium per litre, 6% carbohydrate): 73.9%.^[1]
• Oral rehydration solution (45 mmol of sodium per litre, 2.5% carbohydrate): 76.9%. It cut urine most in the first hour.^[1]

One author had received fees from two nutrition companies.^[1]

A review of 19 studies for first aid found that carbohydrate-electrolyte drinks, best with 4% to 9% carbohydrate, may rehydrate better than water after exercise. It suggests them when normal food is not available.^[5] A second review found that skimmed or low-fat milk rehydrated better than water and coconut water did not. There was too little evidence on beer, and the certainty was very low.^[6]

During exercise

A 2022 meta-analysis of 28 studies found that drinks less concentrated than blood kept blood volume best during continuous exercise, better than water and better than stronger drinks.^[7] In a trial of 12 people who cycled for 60 minutes at about 33 °C, water, a sodium-potassium drink and coconut water gave the same results.^[3]

Why sodium helps

1. The small intestine takes up sodium and glucose together, and water follows them.^[8]
2. A drink more concentrated than body fluids first pulls water into the gut.^[8]
3. Plain water contains very little electrolyte, so it does not replace what sweat takes out.^[9]

What is still unknown

The trials described here had 12 to 72 people and followed them for a few hours.^[2][1][3] One review rated the certainty of its evidence as very low.^[6] How much sodium a person needs depends on how much and how salty they sweat, which differs a lot between people.^[10]