PARIS—New data from a population-based cohort study appear to challenge the belief that survival is linked to daily fluid intake.

The findings, released at the 49th Congress of the European Renal Association-European Dialysis and Transplant Association, showed that total daily fluid consumption had no effect on either all-cause or cardiovascular mortality.

“There was a paper a long time ago that suggested that eight glasses of water a day may improve health, and that ‘assumption’ quickly gained traction so that it is now widely believed without having been rigorously tested,” Suetonia Palmer, MD, senior lecturer at the University of Otago in Christchurch, New Zealand, said. 

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The eight, eight-ounce glasses of water that are routinely recommended for daily intake is the equivalent of about 1.9 liters.

Dr. Palmer and her associates used information from a population registry to examine the association between the intake of non-caffeinated fluids and risks of all-cause and cardiovascular death in adults aged 49 years or older.  

Fluid intake was determined by a self-administered food frequency questionnaire and divided into four quartiles.  The lowest quartile was less than 2.1 liters per day (the equivalent of eight glasses) , and the highest quartile was greater than 3.1 liters per day (the equivalent of 12.5 glasses per day).

Results from 3,858 individuals during a median follow-up of 13.1 years showed an average reported daily fluid consumption of 2.48 L/day. Overall, there were 1,047 deaths and 691 cardiovascular deaths.

Compared with the lowest fluid intake, the adjusted rate for death from any cause did not differ significantly for each quartile of increasing daily fluid intake.

Likewise, researchers observed no association between cardiovascular mortality and fluid intake across quartiles of daily consumption nor any evidence a dose-response relationship between increasing daily fluid consumption (in 100 mL increments) and either all-cause  or cardiovascular mortality.

“So, while our data suggest that there is no relationship between the amount of fluid you consume and your risk of all-cause or cardiovascular mortality over a period of about 10 years and also no relationship with more subtle gradations of fluid intake, our study was retrospective,” Dr. Palmer said.

She added that prospective studies of fluid intake and risk of death or chronic kidney disease are now warranted.  “Patients want to be told that a certain level of fluid intake is nephroprotective but we don’t have that information yet,” she said.