Less salt, less loss of renal function for chronic kidney patients

Patients with chronic kidney disease who react well to antihypertensive medication benefit from limiting their salt intake. The less salt they eat, the better able they are to prevent advancing renal function loss. The chances of becoming dependent on dialysis in the long term are thus reduced.

UMCG renal specialist Prof. Gerjan Navis, PhD student Stefan Vegter and Prof. Maarten Postma (Department of PharmacoEpidemiology & PharmacoEconomics, University of Groningen) conducted the study in cooperation with researchers from the Mario Negri Institute in Bergamo, Italy. The results were published yesterday in the authoritative Journal of the American Society of Nephrology.
 
The best available treatment for kidney patients is directed towards lowering blood pressure and reducing protein loss in the urine by means of medication that blocks the renin-angiotensin-aldosterone system (RAAS). Unfortunately, the treatment is not always sufficiently effective, so that some patients do become dependent on kidney dialysis in the long term. Earlier research had revealed that limiting salt intake improved renal function in the short term by improving blood pressure reduction and lowering protein loss in the urine. This study is the first to investigate the long-term effects.

Long-term effects

Five hundred patients with chronic kidney disease participated in the study. All of the patients were advised to keep a sharp eye on their salt intake. Blood pressure was very strictly regulated in all patients with medication, regardless of their salt intake. After 4 years, there was a clear effect visible with low salt intake. In the group of patients with low salt intake (less than 7 grams of salt a day, which is in line with the advice about salt intake for the general public) only 20% needed dialysis; in the group with high salt intake (14 grams of salt or more a day) this was 60%. In those patients who used excessive amounts of salt, the protein in the urine did not react to the treatment with medication, despite the well-regulated blood pressure. Excessive salt intake thus inhibits the protein-reducing effect of RAAS blockers, with the result that renal function loss continues and dialysis becomes essential. 

Advice

The researchers have been able to show for the first time that too much salt leads to a faster loss of renal function, and in addition that the damaging effect of excessive salt intake on the kidneys occurs even if the blood pressure is properly regulated. They emphasize the importance of avoiding too much salt intake, not only when treating high blood pressure and with cardiovascular disease, but also to preserve renal function. What is remarkable is that the positive effects of reducing salt intake were found at salt intake levels that match the recommendations for a healthy diet; in other words, do not add salt when cooking and avoid salty foods and snacks. With relatively simple lifestyle measures, it thus turns out to be possible for kidney patients to potentially achieve significant health benefits. 

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