Effects of Reduced Dietary Sodium and the DASH Diet on GFR: The DASH-Sodium Trial

Background A potassium-rich Dietary Approaches to Stop Hypertension (DASH) diet combined with low sodium reduces BP. However, the effects of sodium reduction in combination with the DASH diet on kidney function are unknown. We determined the effects of sodium reduction and the DASH diet, on eGFR using cystatin C. Methods DASH-sodium was a controlled, feeding study in adults with elevated or stage 1 hypertension, randomly assigned to the DASH or a control diet. On their assigned diet, participants consumed each of three sodium levels for 30 days after a 2-week run-in period of a high sodium-control diet. The three sodium levels were low (50 mmol/d), medium (100 mmol/d), and high (150 mmol/d). The primary outcome was change in eGFR based on cystatin C. Results Cystatin C was measured in 409 of the original 412 participants, of which 207 were assigned the DASH diet and 202 to the control diet. Compared with control, the DASH diet did not affect eGFR (beta=-0.96 ml/min per 1.73 m(2); 95% confidence interval [CI], -2.74 to 0.83). By contrast, low versus high sodium intake decreased eGFR (beta=-2.36 ml/min per 1.73 m(2); 95% CI, -3.64 to -1.07). Together, compared with the high sodium-control diet, the low sodium-DASH diet decreased eGFR by 3.10 ml/min per 1.73 m2 (95% CI, -5.46 to -0.73). This effect was attenuated with adjustment for diastolic BP and 24-hour urinary potassium excretion. Conclusions A combined low sodium-DASH diet reduced eGFR over a 4-week period. Future research should focus on the effect of these dietary interventions on subclinical kidney injury and their long-term effect on progression to CKD.