Thirty-seven RCTs reported blood pressure and adverse effect outcomes; 14 cohort studies and five RCTs reported cardiovascular outcomes. There were also nine trials and one cohort study in children. Most RCTs had duration of less than three months (range four weeks to 36 months). Cohort studies had follow-up times ranging from 3.8 to 22 years. RCTs were judged to be at low risk of serious bias. Cohort studies were judged to have little risk of serious bias beyond that inherent in observational studies. Studies in children were judged to be at risk of bias.
Blood pressure and adverse events
Reduced sodium intake lowered resting systolic blood pressure (MD 3.39mmHg, 95% CI 2.46 to 4.31; 36 studies, 6,736 participants; Ι²=65%) and lowered resting diastolic blood pressure (MD 1.54mmHg, 95% CI 0.98 to 2.11). Systolic blood pressure lowering was greater in participants with hypertension (MD 4.06 mmHg, 95% CI 2.96 to 5.15; 24 studies; Ι²=29%), than in those without hypertension (MD 1.38 mmHg, 95% CI 0.02 to 2.74; seven studies; Ι²=38%). Results from a number of other subgroup analyses were presented. Reduced sodium intake was found to have no adverse effect on lipid levels (11 studies, 2,339 participants), adrenaline levels, catecholamine levels or renal function. There was no evidence of publication bias.
Mortality and cardiovascular events
Higher sodium intake was associated with a greater risk of stroke generally (RR 1.24, 95% CI 1.08 to 1.43; 10 studies, 72,878 participants; Ι²=49%), of fatal strokes in particular (RR 1.63, 95% CI 1.27 to 2.10; three studies, 48,645 participants; Ι²=33%) and with a greater risk of fatal coronary heart disease (RR 1.32, 95% CI 1.13 to 1.53; three studies, 30,670 participants; Ι²=0). Higher sodium intake increased the risk of all-cause mortality and cardiovascular events generally but results were not statistically significant.
In studies in children reduced sodium intake lowered resting systolic blood pressure (MD 0.84mmHg, 95% CI 0.25 to 1.43; nine studies; Ι²=21%) and diastolic blood pressure (MD 0.87mmHg, 95% CI 0.14 to 1.6). No studies in children reported data on adverse events.