Cardiovascular diseases are the leading cause of death globally, with high blood pressure being a major risk factor for premature deaths. Insufficient dietary potassium and excess dietary sodium are common causes of high blood pressure.
Study: Effects of salt substitutes on clinical outcomes: a systematic review and meta-analysis. Image Credit: Andrey_Popov / Shutterstock.com
Several previous randomized trials have reported that potassium supplementation and reduced sodium intake can lower blood pressure. These blood pressure lowering effects can be found in sodium-reduced and potassium-enriched salt substitutes, where the sodium chloride (NaCl) content of regular salt is replaced with potassium chloride (KCl).
Recently, the Salt Substitute and Stroke Study (SSaSS), which is a five-year cluster randomized trial involving 600 villages in China, provided evidence that salt substitutes can protect against death, cardiovascular events, and stroke. SSaSS also addressed concerns regarding the adverse impact of dietary potassium supplementation and the risk of hyperkalemia. The improvement in clinical outcomes observed in SSaSS is mostly mediated by lowering blood pressure.
A new Heart journal study provides a systematic review of the impact of salt substitutes on clinical outcomes and blood pressure for all available trials. The researchers also sought to determine the constancy of the findings across diverse geographies and populations.
About the study
The study involved searches on Embase, Cochrane, and MEDLINE databases for keywords such as low-sodium salt, salt substitute, potassium salt, and reduced-sodium salt through August 31, 2021.
All studies where clusters or adults were randomly assigned to a regular salt or salt substitute were included. Mortality, blood pressure, cardiovascular events, and cardiovascular mortality were the most common outcomes.
The titles and abstracts of the studies were screened by one author to assess eligibility, while the full-text versions were independently reviewed by the authors. Differences between reviewers were solved through a reference with a third author.
The participant and study characteristics, as well as all outcomes, were extracted from the records. The risk of bias for all studies was also determined independently.
Three cluster-randomized trials, 17 individually-randomized trials, and one step-wedged randomized trial were included in the current analysis. Of the included studies, 11 were in the World Health Organization (WHO) Western Pacific Region, five in the WHO European Region, one in the WHO South-East Asian Region, and four in the WHO Region of the Americas.
The duration of intervention ranged from one to 60 months. The NaCl proportion in the salt substitutes varied from 33% to 75%, while the KCl proportion varied from 25% to 65%.
The mean baseline systolic blood pressure (SBP) was between 113 mm Hg and 177 mm Hg, while the mean baseline diastolic blood pressure (DBP) was within the range of 71 mm Hg and 105 mm Hg.
The mean baseline 24-hour sodium excretion in urine was between 2.9 g and 5.5 g, while the mean daily 24-hour potassium excretion in urine was between 0.8 g and 3.6 g. The overall risk of bias was high for two studies, of some concern for eight studies, and low for 11 studies.
An overall −4.61 mm Hg reduction in SBP, along with a −1.61 mm Hg in DBP, was observed with salt substitutes as compared to controls. Trial durations for less than 12 months were associated with greater reductions in DBP and SBP.
A lower proportion of NaCl in the salt substitute and a higher intake of potassium at baseline were observed to be associated with greater reductions in DBP. Moreover, these results were found to be consistent across various geographical regions and populations.
Furthermore, five studies reported effects on mortality, two on major cardiovascular events, and three on cardiovascular mortality. However, six studies reported no serious adverse events associated with hyperkalemia, while two reported no effect of salt substitute on the serum potassium levels.
Salt substitutes also reduced urinary sodium excretion by −0.48 g/day and increased urinary potassium excretion by 0.45 g/day. The impact on potassium excretion was highest in the European regions and least in the Southeast Asian region. Moreover, the increase in urinary potassium secretion was higher in men.
The current study demonstrated that salt substitutes can lead to consistent blood pressure-lowering effects across diverse populations and geographies without causing any severe adverse events.
Salt substitutes can be adopted in public health policies and clinical practice for the reduction of dietary sodium intake. Furthermore, these substitutes can increase dietary potassium intake to ultimately reduce blood pressure and prevent serious cardiovascular diseases.
Complete data was not available for many studies, and the grey literature was not searched. An additional limitation was that the number of available trials is relatively small.
Limited data on non- hypertensive individuals makes drawing definite conclusions difficult. Finally, the data on clinical outcomes were primarily obtained from one trial.
- Yin, X., Rodgers, A., Perkovic, A., et al. (2022). Effects of salt substitutes on clinical outcomes: a systematic review and meta-analysis. Heart. doi:10.1136/heartjnl-2022-321332.