Is ‘drink plenty of fluids’ good advice?

People tend to take for granted that they should drink more fluids than usual during respiratory infections. But that conventional wisdom has never been rigorously tested, say Australian researchers. Definitive studies are needed because excess fluid intake could cause harm in people with some respiratory ills, the scientists argue in the Feb. 28 British Medical Journal.

Staying well hydrated during colds and infections of the upper respiratory tract presumably makes mucus runny—the better for removing pathogens—and replaces body water that evaporates faster than usual because of fever. But when Chris B. Del Mar of the University of Queensland in Herston, Australia, and his two colleagues reviewed medical studies dating as far back as 1966, they were unable to find even a single trial that evaluated the relationship between fluid intake and the severity of respiratory infections.

On the other hand, the researchers came across several reports of people with lower-respiratory infections, such as pneumonia, who had blood-sodium deficiencies that could have been caused by taking in too much fluid. Given that the “drink plenty of fluids” credo is so ingrained, it would behoove the medical community to test the recommendation’s therapeutic value, the researchers say.