The old saw about drinking eight glasses of water a day for overall health is widely considered a myth.
But research over the years has suggested that drinking extra water helps the kidneys clear sodium, urea and toxins from the body. And in the past year, two large studies found a lower risk of long-term kidney problems among people who drink more water and other fluids daily.
In a report published in the journal Nephrology in March, researchers at the University of Sydney in Australia and elsewhere followed more than 2,400 people older than 50. Those who drank the most fluids, about three liters daily, had a "significantly lower risk" of chronic kidney disease than those who drank the least.
And in a study published last month in The Clinical Journal of the American Society of Nephrology, Canadian scientists followed 2,148 healthy men and women, average age 46, for seven years. They looked at markers of kidney function and health and used urine volume to determine how much fluid the subjects drank daily. After controlling for diabetes, smoking, medication and other factors, they found that those who had the highest urine volume — in other words, those who drank the most fluids — were least susceptible to declines in kidney function.
The findings, the authors said, do not support "aggressive fluid loading," which can cause side effects. But they do provide evidence that moderately increased fluid intake, above two liters daily, "may in fact benefit the kidney."
"Believe it or not, there now does seem to be some merit and evidence to support the 'myth' that eight large glasses of fluid a day is good for your kidneys," said Dr. William Clark, an author of the study and a nephrologist at the London Health Sciences Center in Ontario.
THE BOTTOM LINE: A moderately increased intake of fluids may protect the kidneys.