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A cautionary tale about advice to ‘drink plenty of fluids’ when sick

Drinking too much water (overhydrating) can lead to abnormally low levels of sodium in the body.

Drinking too much water can lead to abnormally low levels of sodium in the body.

The idea that adults must drink eight 8-ounce glasses of water a day to stay hydrated — and therefore healthy — has been thoroughly debunked.

What scientists now recommend is that we drink fluids (preferably water) primarily when we’re feeling thirsty, and that we pay particular attention to satisfying that thirst when it’s hot and humid and/or when we’re exercising strenuously.

But, as the experts also stress, we shouldn’t overdo it. That’s because drinking too much water (overhydrating) can lead to abnormally low levels of sodium in the body. Cells, including those in the brain, may then begin to swell with water — a potentially life-threating condition known as hyponatremia.

Symptoms of hyponatremia include headache, nausea, vomiting, fatigue, disorientation and difficulty speaking. If left untreated, seizures, coma and death may occur.

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A 2013 study estimated that about 2 percent of Americans develop hyponatremia during any given year, and that 11 percent of those people die from complications related to the condition.

Most of those cases of hyponatremia are not caused by drinking water too much water, but by an existing heart or kidney problem that makes it difficult for the body to excrete fluids. But recent research has shown that the condition also occurs with surprising frequency among athletes, particularly those involved in endurance sports.

In a 2002 study, for example, 13 percent of 488 Boston Marathon runners were found to have hyponatremia after the race, and 0.6 percent of the runners had severe cases of it.

Others at risk

Last week, two British doctors extended concerns about drinking too much water to people who are feeling unwell. Writing in the journal BMJ Case Reports, they say that doctors may need to add some caveats to the standard advice they give to patients ill with a viral or other infection to “drink plenty of fluids” and “keep well hydrated.”

One patient who followed that advice too vigorously had to be hospitalized as a result, they explain.

That patient was a 59-year-old woman who showed up at the emergency department of the King’s College Hospital in London with a urinary tract infection (UTI). She had no history of other illnesses and took no regular medications. 

The emergency department doctors prescribed the woman antibiotics and pain medication, but noticed a deterioration of her symptoms.

“She became progressively shaky and muddled,” write Dr. Laura Christine Lee and Dr. Maryann Noronha. “She vomited several times, and was tremulous and exhibited significant speech difficulties.” 

The mystery solved

The doctors became worried that the woman was experiencing a stroke. But then the woman’s partner told them an important bit of information:

Her partner described that the patient had woken up that Sunday morning with dysuria [pain while urinating] and lower abdominal pain, which she had attributed to her recurrent UTI. Throughout the day she had consumed several litres of water based on medical advise she recalled from previous similar episodes.

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Suspecting hypernatremia, the doctors ordered blood tests, which quickly revealed that the woman’s sodium level was significantly below the normal range. They admitted her to the hospital and restricted her fluid intake. The following morning, her blood tests were normal and she felt improved. She was sent home — with instructions, presumably, not to overdo it with her water consumption.

‘A paucity of evidence’

As Lee and Noronha emphasize, cases of hypernatremia in people with normal kidney function are rare but not unknown.

“This [case] mirrors a previous case report in which a young, previously healthy female drank excessive amounts of water during an episode of uncomplicated gastroenteritis, resulting in acute hyponatraemia and death,” they write (with the British spelling of the condition).

Lee and Noronha suggest that the medical community needs to do more research in order to “qualify our oft-given advice to drink more fluids.” 

“There is a paucity of evidence behind the advice to ‘drink plenty of fluids’ in the management of mild infective illness,” they conclude. “This needs to be addressed, especially considering the significant morbidity and mortality of acute hyponatraemia.”

FMI: You can read the case report in full on the BMJ Case Reports website.