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Guppy, Mickan and Mar examined the evidence behind this recommendation. It is based on the theoretical benefits of replacing insensible fluid losses from fever and respiratory tract evaporation, correcting dehydration from reduced fluid intake and reducing the viscosity of mucus. The authors found that giving increased fluids to patients with respiratory infections is not always to be recommended and may be harmful in some cases. For example, fluid restriction is advisable in patients who develop hyponatraemia. Careful monitoring with restricted fluid intake is becoming standard management for bronchiolitis due to the increased secretion of antidiuretic hormone that has been observed in this condition. The authors therefore concluded that doctors should exercise caution in giving advice about increasing fluid intake, especially for patients with infections of the lower respiratory tract.(i,ii)

Kalhoff(iii) considered the basic physiological mechanisms in the lung and airways and found that water transport and local hydration status do contribute to efficient lung function, particularly in perinatal ventilation, mucociliary clearance and asthma. Notably, some expert groups recommend hydration as a complementary asthma therapy. However, more studies are needed to confirm whether mild dehydration is a risk factor in broncho-pulmonary disease.

Last updated: November 2004

(i) Guppy MPD, Mickan SM and Mar CBD. “Drink plenty of fluids”: a systematic review of evidence for this recommendation in acute respiratory infections. BMJ 2004;328:499-500
(ii) Guppy MPD, Mickan SM and Mar CBD. “Drink plenty of fluids” Authors’ reply. BMJ 2004;328:958
(iii) Kalhoff H. Mild dehydration: a risk factor of broncho-pulmonary disorders? European Journal of Clinical Nutrition 2003;57(Suppl 2):S81-87