Do electrolytes help with dehydration from diarrhea?

What the reviews found

A Cochrane review compared drinking a rehydration solution with fluids through a drip (intravenous fluids) in children with gastroenteritis. It pooled 17 trials with 1,811 children, of poor to moderate quality.^[2]

• Treatment failed 4 percentage points more often with the drink: 1 child in 25 needed a drip in the end.^[2]
• Weight gain, low or high blood sodium, how long diarrhea lasted and how much fluid children took did not differ.^[2]
• Children on the drink left hospital 1.2 days sooner.^[2]
• Inflamed veins were more common with the drip. A stopped gut (paralytic ileus) was more common with the drink, but not with the low osmolarity WHO solution.^[2]

Another Cochrane review tested solutions with less sodium and glucose than the old WHO formula, in children in hospital. In 8 trials, the odds of an unplanned drip were 41% lower (odds ratio 0.59). Children also had less stool and vomited less, and low blood sodium was not more common.^[3]

Since 2004, WHO recommends an osmolarity below 270 mOsm/L.^[4] A 2016 Cochrane review of 35 trials with 4,284 people tested solutions made with rice or another starch instead of glucose. Against the old formula, these solutions gave 65 mL/kg less stool in the first 24 hours and diarrhea about 8 hours shorter, from low-quality evidence. Against the current formula, there were too few trials to be sure.^[4]

Why it works

1. Diarrhea takes water out of the body together with sodium, chloride, potassium and bicarbonate.^[1]
2. In the small intestine, sodium and glucose are taken up together, and water follows them.^[5][6]
3. The solution replaces the water and electrolytes lost in stool.^[1]

How it is given

The WHO solution is clean water, salt and sugar, and it costs a few cents per treatment.^[1] WHO adds zinc tablets for 10 to 14 days, which shorten diarrhea by 25%. Severe dehydration or shock needs fluids by drip. Food, including breast milk, should continue.^[1]

In the UK, the NHS says a pharmacist can recommend a solution. They are powders that are mixed with water. A person who feels sick should start with small sips. Young children should not get fruit juice or fizzy drinks, because these can make diarrhea or vomiting worse.^[7]

When to get help

The NHS lists these signs of serious dehydration that need urgent help:^[7]

• unusual tiredness, or a child who seems drowsy^[7]
• dizziness on standing that does not go away^[7]
• dark yellow pee, peeing less, or fewer wet nappies^[7]
• fast breathing or a fast heart rate^[7]
• few or no tears, or a sunken soft spot on a baby's head^[7]

WHO also advises seeing a health professional when diarrhea lasts 14 days or more or there is blood in the stool.^[1]

What is still unknown

Most trials were in children, many in hospital, and the quality of the drip comparison was poor to moderate.^[2][3] Whether starch-based solutions beat the current WHO formula is not settled.^[4]