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Low-sodium salt substitute diet may lower systolic, diastolic BP
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Implementing low-sodium salt substitutes in a diet can lead to a significant lowering of systolic and diastolic BP, according to a meta-analysis published in Heart.
Adrian V. Hernandez, MD, PhD, FACC, FESC, associate professor of comparative effectiveness and outcomes research in the department of pharmacy practice at the University of Connecticut, and colleagues conducted a systematic review and meta-analysis to examine the effect of low-sodium salt substitutes in reducing CVD.
“One of the several existing salt reduction strategies is the use of salt products containing lower concentration of sodium, usually replaced by potassium and other minerals,” Hernandez and colleagues wrote. “These low-sodium salt substitutes are available in industrialized as well as developing countries. If this alternative demonstrates effectiveness on outcomes, it could be targeted as simple public health intervention.”
The researchers analyzed 21 randomized controlled trials enrolling adult hypertensive or general populations comparing detected hypertension, systolic BP, diastolic BP, overall mortality, stroke and other CV factors. Low-sodium salt substitute formulations were heterogenous across studies.
Low-sodium salt substitutes decreased systolic BP (mean difference, –7.81 mm Hg; 95% CI, –9.47 to –6.15) and diastolic BP (mean difference, –3.96 mm Hg; 95% CI, –5.17 to –2.74) compared with the control group, the researchers reported.
Levels of urinary potassium (mean difference, 11.46 mmol per day; 95% CI, 8.36-14.55) and calcium excretion (mean difference, 2.39 mmol per day; 95% CI, 0.52-4.26) increased in those taking low-sodium salt substitutes, Hernandez and colleagues wrote. A decrease in urinary sodium excretion (mean difference, –35.82 mmol per day; 95% CI, –57.35 to –14.29) was also observed with low-sodium salt substitutes. There were no significant differences in detected hypertension, overall mortality, total cholesterol, triglycerides, glucose or BMI.
“We could not conclude on the effects of salt substitutes’ stroke or CV mortality due to the scarcity of data,” Hernandez and colleagues wrote. “Further, well-powered, phase 3 [randomized controlled trials] are necessary to elucidate the effects of low-sodium salt substitutes on clinical and intermediate outcomes in hypertensive and general populations.” – by Earl Holland Jr.
Disclosures: The authors report no relevant financial disclosures.
Perspective
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Franz H. Messerli, MD, FACC
Because the outcomes quite clearly show that BP can be lowered with a low-salt substitute it is, to some extent, a little bit disappointing that a low-sodium salt substitute does not fulfill the hypothesis of the author that it should reduce morbidity and mortality. Yes, BP goes down, but no, there’s no effect on morbidity and mortality.
So, the question that comes up automatically is ‘why is this the case?’
There are a variety of possibilities. I think the most important one we always forget is that BP remains a surrogate endpoint.
In general, it goes in parallel with stroke, MI and mortality, but not always. It remains a surrogate endpoint and it’s entirely possible that under certain circumstances, there are discrepancies between BP and the risk for stroke and MI, and this may be one possibility here.
A meta-analysis is not a randomized trial and suffers from its inherent pitfalls. As Hernandez and colleagues stated, it would be nice to have a randomized, prospective trial over a prolonged period, but this is probably not going to happen.
Looking at the literature in aggregate, it seems reasonable to recommend a low-sodium diet in hypertensive persons, because with a low-sodium diet, we can lower BP some.
However, the percentage of patients who will indeed be able to go and to stay on a low-sodium diet over a prolonged period of time is small. Still, a low-salt sodium substitute may prove to be useful, and I think that it’s most important usefulness comes from the fact that sodium is mostly replaced by potassium. We know that potassium does have a beneficial effect on CVD and particularly on the risk of stroke. Even for patients who are on a relatively high-salt diet, increasing potassium intake may confer a protective effect regarding BP elevation.
So, in this regard, despite the disappointing overall CV effects in the above study, salt substitutes are to be welcome.
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