THURSDAY, Feb. 26, 2004 (HealthDayNews) -- Drinking plenty of fluids when you have a common cold is age-old advice that has no supporting proof at all, says surprising new research out of Australia.
"There is no empirical evidence on whether it is effective or not, but some indirect evidence that it might be harmful," says Dr. Chris B. Del Mar, a professor of general practice at the University of Queensland.
Del Mar trolled medical databases going back a quarter-century or more, looking for studies on fluid intake in patients with respiratory infections. His search found no indication of any randomized, controlled trial, the gold standard for research.
But he did find several reports of patients with respiratory infections who developed hyponatremia, a potentially troublesome depletion of sodium in the blood that can result from excessive fluid intake.
"These patients were all successfully treated with fluid restriction," says his report in the Feb. 28 issue of the British Medical Journal.
Del Mar also found two studies reporting the same kind of sodium depletion in at least a third of children with moderate to severe pneumonia. Four children with severe sodium depletion died.
Until controlled studies are done, Del Mar writes, "we should be cautious about universally recommending increased fluids to patients, especially those with infections of the lower respiratory tract."
It's not likely that such a study will be done, he says, because "this would be a very difficult trial to mount."
A very large number of patients would have to be studied, because the complications caused by excessive fluid intake are rare, he adds.
Still, there is some evidence that excessive accumulation of fluid in the brain could cause damaging fits, he says.
Del Mar says he did his study because "it is my job to think about anything we do, and not take anything for granted."
Family doctors in Australia usually do recommend more fluid intake in respiratory infections, as is true in Great Britain and the United States, he says.
The origin of that advice is unclear, he adds.
"We think it arose in ancient times," he says. "We don't know where it came from. It just gets passed on."
True enough, says Dr. Jim D. King, who is on the board of directors of the American Academy of Family Physicians.
"What this paper tells me is that a lot of the things we take for granted to be true may not be true," says King, who is in private practice in Selmer, Tenn.
However, he addes, the studies cited by Del Mar don't necessarily show that extra fluid intake can be dangerous.
"The studies didn't take into consideration whether the people were taking a lot of fluids," he says. "But they do indicate that we should be looking at sodium levels more carefully."
But King agrees with the basic point: "There is nothing in the literature to document that increased drinking of fluids is beneficial."
In his practice, King says, he does not routinely tell patients with lower respiratory tract infections to increase fluid intake -- unless they show signs of dehydration.
Advice on how to handle a common cold is offered by the National Institute of Allergy and Infectious Diseases -- which recommends extra fluids -- or the American Academy of Family Physicians.