Proteinuria found in many people with polyuria.

LONDON, Ont.—Drinking two liters of water per day may not benefit most individuals and even could be harmful, investigators say.

At the Canadian Society of Nephrology annual meeting here, re-searchers from the University of Western Ontario, also in London, presented a study showing a significant correlation between excess urine production—which is usually caused by excess fluid intake—and proteinuria.

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The large population-based study un-covered a fivefold higher risk of proteinuria among people with polyuria than among those with normal urine volume, even after taking into account such factors as age, sex, and estimated glomerular filtration rate.

If investigators replicate this finding, further research should be conducted to determine the renal consequences of drinking two liters of water per day, said lead investigator Jessica Sontrop, PhD, assistant professor in the department of epidemiology and biostatistics.

“Such a finding would have important implications, given the silent nature of kidney disease and the widespread, but unsubstantiated, belief that drinking eight glasses of water per day is healthy.”

The finding of proteinuria in people with polyuria was first made by W.F. Clark, MD, a nephrologist and chair of the Walkerton (Ontario) Health Study Operations and Research Committee. During routine screening, he observed proteinuria and polyuria in 100 adults with no medical history, medication use, or renal testing abnormality to explain their condition.

Proteinuria was reduced in these subjects after restricting fluid intake, indicating the cause was voluntary fluid intake (CMAJ. 2008;178:173-175). Dr. Sontrop and five investigators affiliated with the Walkerton Health Study subsequently conducted an analysis of all 3,098 participants. Of these subjects, 490 had proteinuria; in all but 23, the condition was mild.

When managing patients with polyuria and proteinuria, nephrologists may want to obtain a series of 24-hour urine collections after a period of moderate fluid-intake restriction, Dr. Sontrop suggests. This should indicate whether the proteinuria is tied to excess fluid intake or to some other factor.

Nephrologist Stanley Goldfarb, MD, professor of medicine at the University of Pennsylvania in Philadelphia and a specialist in renal electrolytes and hypertension, suggests caution before al-tering clinical practice based on this observational study.

“It is not clear why drinking more fluid would lead to increased protein excretion,” Dr. Goldfarb said. “It may be that measuring very small amounts of protein in large volumes of urine introduces some systematic error; it is also unclear why [the individuals involved] drank so much fluid. Do they have a history of kidney problems, or do they have an occupation which exposes them to some factor that provokes proteinuria? But the results are worthy of further study.”