Virtually all respiratory tract infections are caused by viruses or bacteria. Upper respiratory infections (URIs) affect the nose, ears, and throat, and include the common cold , the flu , and strep throat . While URIs are generally mild and temporary, they can lead to more serious infections, such as lower respiratory infections like bronchitis and pneumonia .

The recommendation to drink a lot during a respiratory infection makes sense, because the extra fluid presumably replaces fluid losses, prevents dehydration , and loosens the mucus that often builds up in the respiratory tract. Nevertheless, there is no clear evidence that extra fluids during a respiratory infection have a benefit.

Some researchers propose that there actually could be a potential risk associated with drinking excess fluids. During a respiratory infection, your body secretes high levels of antidiuretic hormone, which acts on the kidneys to retain water. Theoretically, excess water combined with high levels of antidiuretic hormone could lead to salt loss (hyponatremia) and fluid overload. In extreme cases, severe hyponatremia can lead to irritability, confusion, lethargy, coma , and convulsions.

So does drinking extra fluids during a respiratory infection have benefits, or does it have the potential to cause harm? A new study in the February 28, 2004 issue of the British Medical Journal found no evidence that extra fluids during respiratory infections is beneficial, and scant evidence that it might even be harmful.

About the Study

For this study, the researchers performed a systematic review of the results of existing studies to determine the following:

  • Does increasing fluid intake during respiratory infections decrease the duration and severity of symptoms?
  • Are there any adverse effects associated with increasing fluid intake during respiratory infections?
  • Are the consequences of increased fluid intake during respiratory infections associated with the site of the infection (upper or lower respiratory tract) or the severity of the illness?

The Findings

The researchers found that there were no randomized controlled trials—the gold standard in clinical research—comparing the effects of increased versus restricted fluid intake during respiratory infections.

They did, however, find two studies that reported high rates of hyponatremia (31% and 45%) in children with moderate to severe pneumonia. None of the children in these studies showed symptoms of dehydration, but four children with low sodium levels died during the study.

The researchers also found several case studies of patients with respiratory infections who developed hyponatremia.

It is important to note that these findings have some major limitations. First, this analysis is only as good as the studies that comprised it. And since no randomized trials were evaluated, its results should not be considered completely reliable. Furthermore, the studies linking hyponatremia to respiratory infections do not necessarily indicate that excess fluids are the cause of the hyponatremia.

How Does This Affect You?

These findings suggest that the recommendation to drink plenty of fluids during a respiratory infection may not be warranted. The general consensus among healthcare providers has been that consuming excess fluids during a respiratory infection is at worst harmless. While this is still probably true, the findings from this study suggest that further investigation would certainly be worthwhile. A randomized controlled trial investigating the effects of administering excess fluids versus restricting fluids would help clarify this matter.

Until this evidence is available, what should you do if you develop a respiratory infection? Strep throat, pneumonia, and bronchitis usually require medical treatment, so see your doctor if you suspect you have one of these conditions. On the other hand, colds and the flu usually resolve without medical attention. So for now, if you develop a cold or the flu, perhaps the most prudent recommendation you can follow is to drink a normal amount of fluid unless you show signs of dehydration, which include:

  • Dry mouth
  • Decreased urination, or darker, stronger smelling urine
  • Decreased tear production
  • Eyes that appear sunken
  • Lethargy
  • Lightheadedness