Electrolyte Replacement: Why the WHO Formula Still Beats Sports Drinks

Oral rehydration therapy (ORT) is arguably the most consequential public-health intervention of the 20th century. A systematic review for the Child Health Epidemiology Reference Group estimated that oral rehydration solution (ORS) can prevent about 93% of deaths from diarrhoea in children under five (Munos 2010; PMID 20348131; DOI 10.1093/ije/dyq025). Modern flavoured sports drinks borrow the same concept but use a much lower sodium concentration, which is why they don't replace ORS when illness or heavy sweat loss is the problem.

How the formula works

In the small intestine the SGLT1 transporter pulls sodium and glucose across the gut wall together, and water follows by osmosis. Too little glucose and the pump stalls; too much and the lumen becomes hypertonic, which pulls water out of the body and can worsen diarrhoea. The WHO reduced-osmolarity formula adopted in 2002 is balanced for this cotransport: 75 mmol/L sodium, 75 mmol/L glucose, 65 mmol/L chloride, 20 mmol/L potassium, and 10 mmol/L citrate (total osmolarity ~245 mOsm/L).

Where sports drinks diverge

Most commercial sports drinks contain only 10–25 mmol/L sodium — roughly a quarter of the WHO formula — and 6–8% carbohydrate for taste and fuelling. That ratio is fine for working muscles during exercise, but it isn't enough sodium to maximise rehydration after heavy losses. For endurance events over two hours in the heat, or any GI illness, true ORS-style products (Pedialyte, Hydralyte, DripDrop, WHO-style sachets) deliver more sodium and rehydrate faster.

Clinical evidence for the reduced-osmolarity formula

A Cochrane review in children compared the reduced-osmolarity ORS to the original WHO formula. Pooling 8 trials (1,491 children) for the primary outcome, reduced-osmolarity ORS lowered the odds of needing unscheduled IV fluids (OR 0.59, 95% CI 0.45–0.79), reduced stool output, and reduced vomiting, with no excess hyponatraemia (Hahn 2002; PMID 11869639; DOI 10.1002/14651858.CD002847). A separate Cochrane review of polymer-based (rice or wheat) ORS, which slowly releases glucose, found further small reductions in stool output and IV-fluid need versus glucose ORS (Gregorio 2016; PMID 27959472; DOI 10.1002/14651858.CD006519.pub3). In athletes, urine markers track exercise-induced fluid loss reasonably well, but laboratory studies generally show that drinks with more sodium are retained longer post-exercise than water or low-sodium sports drinks (Hahn & Waldréus 2013; PMID 23994895).

When to use what

For daily hydration: plain water is enough. For 60+ minutes of hard exercise in the heat or 90+ minutes of moderate exercise: a sports drink with 6–8% carbohydrate and ~20–30 mmol/L sodium covers fuelling and modest fluid balance. For diarrhoea, vomiting, hot-weather dehydration, or post-event fluid replacement after heavy sweat loss: use a true ORS-style product or WHO-style sachet, where the higher sodium (45–75 mmol/L range) is what drives rehydration.

Red flags

Severe dehydration — lethargy, no urine for 8 hours, cool mottled skin, or rapid breathing in a child — needs medical care, not home rehydration. Electrolyte sachets that deliver more than 1,000 mg sodium per packet are designed for athletic loss and can raise blood pressure if used daily. People with diabetes should read the carbohydrate label on ORS products: some deliver the equivalent of a soft drink's sugar load.