Salt Intake and Kidney Outcomes in Older Adults With Chronic Kidney Disease: A Stage-Specific Cohort Study

In patients with chronic kidney disease (CKD), salt restriction has been shown to lower blood pressure and proteinuria and to provide kidney protective effects. However, the benefit of salt restriction in older adults with CKD remains unclear, particularly in advanced stages.

We conducted a single-center retrospective cohort study of patients aged ≥ 75 years with CKD (estimated glomerular filtration rate [eGFR] < 60 mL/min/1.73 m²). Salt intake was estimated from spot urine using the Tanaka formula and categorized into quartiles. The primary outcome was a composite kidney endpoint of ≥ 30% eGFR decline or initiation of kidney replacement therapy. Cox proportional hazards models and competing risk analyses were performed, stratified by CKD stage.

A total of 462 patients (median age, 79 years; 68.6% male) were included. Of these, 305 had CKD Stage 3 and 157 had Stages 4-5. During a median follow-up of 2.79 years, 121 patients (26.2%) experienced the composite outcome. In Stage 3 CKD, higher salt intake was significantly associated with increased risk (adjusted HR 2.70; 95% CI 1.02-7.12; highest vs. lowest quartile), and findings were consistent across sensitivity analyses. In contrast, no significant association was observed in Stages 4-5.

Among older adults with CKD, excessive salt intake was associated with adverse kidney outcomes in CKD Stage 3 but not in Stages 4-5. These results suggest that salt restriction may be most beneficial in the early stages of CKD in this population.