Does reducing dietary salt intake lower blood pressure or albuminuria in patients with chronic kidney disease (CKD)?
In patients with CKD, reducing dietary salt intake by approximately 4.2 g per day (73.5 mmol or 1,690 mg of sodium) lowers mean systolic blood pressure by 6.9 mm Hg (95% CI, 5.0 to 8.8 mm Hg) and diastolic blood pressure by 3.9 mm Hg (95% CI, 3.0 to 4.8 mm Hg) compared with patients on a higher salt diet. In patients with CKD who do not have end-stage renal disease, a low-salt diet also decreases mean albuminuria by 36% (95% CI, 26% to 44%) compared with a higher salt diet.1 (Strength of Recommendation: C, disease-oriented evidence.)
CKD is a major global health concern affecting an estimated 9.37% of the world's population, and was the 6th most common cause of non–injury-related death in 2019 in the adult population, accounting for 1.42 million deaths worldwide.2 There has been a 42% increase in deaths among patients with CKD from 2009 to 2019, making it one of the fastest rising major causes of death. The risk of cardiovascular disease and death increases with worsening glomerular filtration rate, which is a measurement used to determine the severity of CKD. Effective strategies for prevention of these negative outcomes might improve patient prognosis and reduce health care costs. Dietary salt intake is a modifiable risk factor thought to reduce progression of CKD, so the authors of this review sought to discern the benefits and harms of reducing dietary salt intake in adults with CKD.
This Cochrane review involved 21 studies with a total of 1,197 randomized participants recruited in the United States, Europe, Asia, and Australia.1 The 2021 update included randomized controlled trials (RCTs) and quasi-RCTs of patients 18 years and older who had CKD and a glomerular filtration rate of less than 60 mL per minute per 1.73 m2, were receiving kidney replacement therapy, had a functioning kidney transplant, or had proteinuria (National Kidney Foundation Kidney Disease Outcomes Quality Initiative stage 1 to 5) or elevated serum creatinine (greater than 1.36 mg per dL [120 μmol per L]). Study duration ranged from one to 36 weeks, with a median of seven weeks. The four-week mark was used as the cut-off to classify short-term vs. long-term intervention. Methods used to determine sodium intake were heterogeneous and included either 24-hour urine sodium excretion (15 studies) or the use of food records or 24-hour patient recall.
Reducing salt intake by 4.2 g per day (73.5 mmol or 1,690 mg of sodium) reduced systolic blood pressure (mean difference [MD] = 6.9 mm Hg; 95% CI, 5.0 to 8.8 mm Hg; high-certainty evidence) as well as diastolic blood pressure (MD = 3.9 mm Hg; 95% CI, 3.0 to 4.8 mm Hg; high-certainty evidence) in short-term (less than four weeks) and long-term (four weeks or more) studies. Ambulatory blood pressure monitoring over the course of 24 hours was used preferentially when more than one blood pressure measurement was reported, and clinic-assessed blood pressures were used preferentially instead of self-assessed measurements. Standing blood pressure was preferred when measurements from more than one position were reported.
In six studies of 436 participants, reducing dietary salt intake decreased the 24-hour urinary protein excretion in patients with CKD stages 1 to 4 (MD = 0.41 mg per day; 95% CI, 0.25 to 0.58 mg per day). Symptomatic hypotension occurred more often with reduced salt intake (number needed to harm = 21; 95% CI, 7 to 83; moderate-certainty evidence) based on data from six studies of 478 participants with CKD stages 1 to 4 in short-term (less than four weeks) and long-term (four weeks or more) interventions. The recorded symptomatic hypotension episodes were mild.
Another meta-analysis of 11 RCTs of 738 patients with CKD stages 1 to 4 showed improvements in blood pressure and proteinuria with moderate dietary salt reduction.3 Considering these data, there is strong evidence that lower dietary salt intake decreases blood pressure, and moderate evidence that it lowers proteinuria in patients with CKD. The National Institute of Diabetes and Digestive and Kidney Diseases recommends total dietary salt intake of less than 2,300 mg per day for patients with CKD.4
The practice recommendations in this activity are available at https://www.cochrane.org/CD010070.
Editor's Note: The number needed to harm and its corresponding CI reported in this Cochrane for Clinicians was calculated by the authors based on raw data provided in the original Cochrane review.
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