New study findings do not support routine low sodium and potassium diets to prevent renal function decline in patients with vascular disease, regardless of the presence or absence of chronic kidney disease.

Andrew Smyth, MD, of McMaster University in Hamilton, Ontario, and colleagues studied 28,879 individuals at high cardiovascular risk who were followed for a mean of 4.5 years in the ONTARGET and TRANSCEND trials. The primary outcome was a 30% or greater decline in estimated glomerular filtration rate (eGFR) or the start of chronic dialysis. During follow-up, the study population had a mean eGFR decline of 1.3 mL/min per 1.73 m2.The primary outcome occurred in 2,052 subjects (7.6%).

The investigators found no association between urinary sodium and potassium excretion and any renal outcome, according to findings published online ahead of print in Kidney International. However, higher potassium excretion was associated with better renal outcomes.

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Compared with the lowest potassium excretion (median 1.7 g/day), moderate (median 2.1 g/day) and high (median 2.7 g/day) excretion was associated with a 12% and 26% decreased likelihood of the primary outcome. “Thus, urinary potassium, but not sodium, excretion predicted clinically important renal outcomes.”

In speculating how high potassium excretion may reduce progression of kidney disease, the authors noted that ONTARGET had found that a diet rich in fruits and vegetables was associated with better renal outcomes. “Obviously such a diet will lead to higher potassium excretion,” they wrote.

“Thus, the potassium effect observed here may entirely be due to a healthy diet, mediated by dietary antioxidants that have anti-inflammatory activity, which may decrease kidney disease progression.”