Abstract
Background
Authoritative medical and public health agencies in most countries advise to reduce population dietary salt intake to under 5–6 g/day as a strategy for preventing high blood pressure and cardiovascular disease. However, there is still dispute about whether salt reduction should be adopted by all populations. In addition, the effect of duration of dietary salt reduction has not been sufficiently investigated.
Purpose
To understand the effect of dietary salt reduction on blood pressure and the impact of intervention duration.
Methods
A systematic review and meta-analysis was conducted. Randomized controlled trials that allocated participants to low and high salt intake, without confounding from unequal concomitant interventions, were included. We excluded studies done in individuals younger than 18 years, pregnant women, individuals with renal disease or heart failure, and studies with sodium excretion estimated from spot urine. Random effect meta-analysis was used to generate pooled estimates of the effect on 24-hour urinary sodium excretion, systolic and diastolic blood pressure. Multivariate meta-regression was used to quantify the dose response effect of dietary salt on blood pressure change and to understand the impact of the intervention duration.
Results
125 studies were included with 162 data points extracted. Ninety-nine data points (61%) had interventions under 4 weeks. Overall, 24-hour urinary sodium excretion changed by −141 mmol (95% CI: −156; −126), systolic blood pressure changed by −4.4 mm Hg (95% CI: −5.2; −3.7) and diastolic blood pressure changed by −2.4 mm Hg (95% CI: −2.9; −1.9). Sodium reduction resulted in a significant decrease of systolic blood pressure in all subgroups except in participants with low baseline sodium intake (<109 mmol) (Figure 1). Each 100 mmol reduction of sodium was associated with 2.7 mm Hg (95% CI: 1.0; 4.4; p=0.002) reduction of systolic blood pressure and 1.2 mm Hg (95% CI: 0.0; 2.4; p=0.046) reduction of diastolic blood pressure after adjusting for intervention duration, age, sex, race, baseline blood pressure, baseline sodium intake and interaction between age and baseline blood pressure. For the same amount of salt reduction, a 10 mm Hg higher baseline systolic blood pressure would result in 2.5 mm Hg greater reduction of systolic blood pressure. There is not enough evidence to show the impact of intervention duration.
Figure 1
Conclusions
Our meta-analysis showed that sodium reduction could reduce blood pressure in all adult populations regardless of age, sex and race. The effect of salt reduction on systolic blood pressure increases with higher baseline blood pressure. Further studies, designed to investigate the impact of intervention duration, are needed to understand the significance of the duration.
Acknowledgement/Funding
None
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