Long-Term Effect of Salt Substitution for Cardiovascular Outcomes

Salt substitution is a simple yet increasingly promising strategy to improve cardiovascular outcomes. To evaluate the long-term effects of salt substitution on cardiovascular outcomes. PubMed, EMBASE, Cochrane CENTRAL, and CINAHL searched from inception to 23 August 2023. Trial registries, citation analysis, and hand-search were also done. Randomized controlled trials (RCTs) comparing provision of or advice to use a salt substitute with no intervention or use of regular salt among adults for 6 months or longer in total study duration. Two authors independently screened articles, extracted data, and assessed risk of bias. Primary outcomes include mortality, major cardiovascular events (MACE), and adverse events at 6 months or greater. Secondary and post hoc outcomes include blood pressure, cause-specific mortality, and urinary excretion at 6 months or greater. Random-effects meta-analyses were done and certainty of effect estimates were assessed using GRADE (Grading of Recommendations Assessment, Development and Evaluation). Of the 16 included RCTs, 8 reported on primary outcomes. Most (n = 7 of 8) were done in China or Taiwan, 3 were done in residential facilities, and 7 included populations of older age (average 62 years) and/or with higher-than-average cardiovascular risk. In this population, salt substitute may reduce risk for all-cause mortality (6 RCTs; 27 710 participants; rate ratio [RR], 0.88 [95% CI, 0.82 to 0.93]; low certainty) and cardiovascular mortality (4 RCTs; 25 050 participants; RR, 0.83 [CI, 0.73 to 0.95]; low certainty). Salt substitute may result in a slight reduction in MACE (3 RCTs; 23 215 participants; RR, 0.85 [CI, 0.71 to 1.00]; very low certainty), with very low-certainty evidence of serious adverse events (6 RCTs; 27 995 participants; risk ratio, 1.04 [CI, 0.87 to 1.25]). The evidence base is dominated by a single, large RCT. Most RCTs were from China or Taiwan and involved participants with higher-than-average cardiovascular risk; therefore, generalizability to other populations is very limited. Salt substitution may reduce all-cause or cardiovascular mortality, but the evidence for reducing cardiovascular events and for not increasing serious adverse events is uncertain, particularly for a Western population. The certainty of evidence is higher among populations at higher cardiovascular risk and/or following a Chinese diet. National Health and Medical Research Council. (PROSPERO: CRD42022327566).