Not much evidence behind advice to 'drink plenty of fluids' when unwell

Doctors often advise patients to 'drink plenty of fluids' and 'keep well hydrated' when unwell, but a new report calls for more research behind this advice.

Writing in the journal BMJ Case Reports, doctors explain the case of a 59-year-old woman who developed hyponatraemia -- a condition that occurs when the level of sodium is abnormally low -- from drinking too much water to help with a recurring urinary tract infection.

The patient was admitted to the Royal London Hospital Emergency Department, and was prescribed antibiotics and painkillers for her urinary tract infection. However, she became progressively shaky, muddled, vomited several times, and had significant speech difficulties.

Tests revealed hyponatraemia - her sodium level was 123 mmol/L (normal range 135-145) - which the doctors say was the cause of these progressively worsening symptoms, and can result from water intoxication.

The patient revealed that throughout the day, she had consumed several litres of water based on medical advice she recalled from previous similar episodes to 'flush out her system'.

The condition is a medical emergency and requires prompt recognition and action. A mortality rate of almost 30% has been reported for patients with sodium levels of less than 125 mmol/L.

Doctors restricted her fluid intake to 1 litre over the following 24 hours, and by the following morning, she felt improved, her blood tests were normal, and she was discharged that day.

Fatal water intoxication has also been reported in endurance exercise, use of the drug MDMA, and anecdotally during university initiation activities as well as during water-based torture rituals.

This incident mirrors a previous case report, in which a woman developed hyponatraemia, and later died from drinking excessive amounts of water during an episode of gastroenteritis.

The doctors say it's very rare to develop water intoxication with normal renal function. However, some illnesses drive up levels of antidiuretic hormones, which reduce renal excretion of water. For these type of conditions, the doctors ask, should increased water intake be recommended?

They conclude: "There is a paucity of evidence behind the advice to 'drink plenty of fluids' in the management of mild infective illness. This needs to be addressed, especially considering the significant morbidity and mortality of acute hyponatraemia."