Impact of sodium intake on blood pressure, mortality and major cardiovascular events: an umbrella review of systematic reviews and meta-analyses

A plethora of systematic reviews with meta-analyses (SRMAs) evaluating sodium intake on cardiovascular health have been published. However, the quality of the SRMAs, that report absolute estimates of effect for major cardiovascular events and the corresponding certainty of the evidence has not been explicitly summarized. We conducted an umbrella review to assess the strength and validity of associations between lower sodium intake and cardiovascular outcomes. We used a modified, more stringent, version of the AMSTAR 2 instrument and the GRADE approach to assess SRMA methodological quality and evidence certainty, respectively. Across three cardiovascular risk strata, we computed the absolute risk reduction (ARR) for binary outcomes. We included 56 SRMAs. In various cardiovascular risk populations, moderate to high certainty evidence suggested that lower sodium intake reduced systolic blood pressure (BP) by -8.69 to -2.00 mmHg, and had concordant but smaller effects on diastolic BP. Salt substitutes conferred a small but important reduction in all-cause and cardiovascular mortality [ARR 12 fewer per 1000; 9 fewer per 1000; respectively], and had little to no effect on the risk of stroke [ARR 1 fewer per 1000]. Moderate to high certainty evidence suggested that lower sodium intake is probably beneficial for the prevention of major cardiovascular events, especially in low cardiovascular risk populations.