CKD Risk Lower in Big Water Drinkers

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MONTREAL—Drinking water may help to protect individuals from chronic kidney disease (CKD), according to investigators.

At the Canadian Society of Nephrology's 2013 annual meeting, researchers reported on an analysis of data from the 2005-2006 National Health and Nutrition Examination Survey (NHANES) data showing that CKD was 2.5 times less likely to develop in people who drank more than 4.3 liters of water a day than those who drank less than two litres a day.

The mechanism is likely to be decreased production of arginine vasopressin, a hormone that has negative effects on renal hemodynamics and blood pressure. Increased water intake suppresses its production, according to the investigators.

The findings also were published recently in the American Journal of Nephrology (2013;37:434-442).

The study focused on 3,426 people who completed a dietary interview and physical examination. The median total water intake was 5.4 l/day in the highest tertile, while it was 2.9 l/day in the medium-water-intake tertile and 1.6 l/day in the lowest tertile. Subjects in the lowest tertile had a higher average age than those in the highest tertile (mean 47 vs. 42 years), a higher percentage of females (69% vs. 35%), lower percentage of non-Hispanic whites (57% vs. 83%), were less likely to have gone beyond a high school education (48% vs. 65%), had a lower percentage of obese subjects (28% vs. 32%), were less likely to be currently smoking (22% vs. 38%), and were more likely to be sedentary (76% vs. 50%) or to have high blood pressure (31% vs. 26%) or diabetes (11% vs. 8%). They also had a considerably lower mean sodium intake (2,595 vs. 4,697 mg/day).

The lowest-tertile group also had the highest percentage (8.4%) of individuals with an eGFR of 30-60 (stage 3 CKD). The average eGFRs for the middle-tertile and highest-tertile groups were 3.7% and 1.3%, respectively. Compared with those in the highest tertile, those in the lowest tertile had a 2.5 times increased risk for CKD after adjusting for age, gender, ethnicity, body mass index, dietary sodium, smoking, hypertension, and diabetes. Subjects in the middle tertile had a 48% increased risk.

The protective effect was almost entirely from plain water rather than water from other types of drinks.

Participants in the lowest tertile of water intake had more cardiovascular disease (CVD), but the investigators' analyses did not turn up a statistically significant association between low water intake and CVD.

The team also has completed a pilot prospective study that shows it is safe to hyperhydrate patients with an estimated glomerular filtration rate of 30 -60 mL/min/1.73 m2, and that participants can be successfully coached to hyperhydrate, said lead investigator William F. Clark, MD, Professor of Medicine at Western University in London, Ontario. The results will be presented at the American Society of Nephrology's annual meeting in October, he said.

Based on the success of the pilot study, Dr. Clark and his team launched a randomized, controlled trial of hyperhydration in April. They are enrolling the first of 700 participants with an eGFR of 30-60, Dr. Clark said. Adult participants are being randomized to drink between 1.0 and 1.5 litres of water a day in addition to their usual fluid intake for one year. Dr. Clark's team will measure subjects' eGFRs every three months and compare their renal function changes with those of controls who have usual fluid intake without drinking extra water.

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