Commentary

The Complicated Relationship Between Sodium Intake and Blood Pressure

AUTHOR:
Michael J. Bloch, MD,
Associate Professor, University of Nevada School of Medicine
Medical Director, Renown Vascular Care, Renown Institute for Heart and Vascular Health
President, Blue Spruce Medical Consultants, PLLC

CITATION:
Bloch MJ. The complicated relationship between sodium intake and blood pressure. Consultant360. Published online January 5, 2022.

It is generally well accepted that populations who consume more salt have higher rates of hypertension and that restriction of sodium intake can lower blood pressure in patients with hypertension. However, the fact that many individuals can consume large amounts of sodium without developing hypertension suggests that the relationship between sodium intake and blood pressure is more complex than commonly appreciated.

In a fascinating recent review of salt handling and blood pressure, Ellison and Welling try to demystify this relationship.1 As they point out, under normal hemodynamic conditions, even small changes in effective circulating volume (ECV) caused by changes in sodium intake will lead to corresponding changes in renal sodium handling to maintain sodium excretion equal to sodium intake. It is clear that many people can maintain normal blood pressure across wide ranges of sodium intake by adjusting sodium excretion accordingly. Yet, some people, often referred to as “salt sensitive,” can have striking changes in blood pressure with even small changes in sodium intake. While most people probably live in the intermediate range of the continuum from salt “sensitive” to “resistant,” a clinical marker of salt sensitivity is not readily available to clinicians.

Traditionally, it has been held that people who are salt sensitive develop hypertension simply because of expansion of ECV, but this does not appear to fit the experimental or clinical evidence. As Ellison and Welling explain in their review article,1 the development and maintenance of salt-sensitive hypertension likely stems from a “mosaic” of multiple pathological underpinnings including renal, neurohormonal, vascular, immunologic, and dietary factors. The fact that potassium intake, increased dietary fiber, and the gut microbiome may all affect salt-sensitive hypertension has particular public health resonance.

In particular, the complex interplay between potassium intake and salt sensitivity is illustrative. Previous studies that examine only sodium intake have shown inconsistent results in terms of reduction in blood pressure and cardiovascular events. A recent Cochrane review demonstrated that as compared with high sodium intake, low sodium intake was associated with only a 0.4 mm Hg reduction in normotensives and a 4 mm Hg reduction in hypertensives.2  This modest effect stands in contrast to more recent studies that suggest that the ratio of sodium to potassium intake may be more important than looking at sodium intake in isolation.

The Dietary Approach to Stop Hypertension (DASH) diet is generally high in potassium (as well as soluble fiber, healthy fats, and nonmeat protein). In the DASH-Sodium study, compared with the control diet with a high sodium level, the DASH-Sodium diet with a low sodium level led to a mean systolic blood pressure that was 7.1 mm Hg lower in participants without hypertension, and 11.5 mm Hg lower in participants with hypertension.3 Additionally, in a recent large cluster-randomized clinical trial performed in 600 rural villages in China, participants who received a potassium-containing salt substitute (75% sodium and 25% potassium) had significantly lower blood pressure and a 14% decrease in the rate of stroke, a 13% decrease in rate of major cardiovascular events, and 12% decrease in the risk of deaths from any cause.4

For the clinician, this information suggests that we likely need to encourage sodium restriction not as an isolated intervention but as a part of a multifaceted lifestyle intervention that includes more healthy eating habits, including increased fiber and potassium intake. As investigators, we need to continue to unlock the secrets of the gut microbiome and the immune system, which may hold additional keys to understanding the link between sodium and blood pressure.

References:

  1. Ellison DH, Welling P. Insights into salt handling and blood pressure. N Engl J Med. 2021;385(21):1981-1993. doi:10.1056/NEJMra2030212
  2. Graudal NA, Hubeck-Graudal T, Jurgens G. Effects of low sodium diet versus high sodium diet on blood pressure, renin, aldosterone, catecholamines, cholesterol, and triglyceride. Cochrane Database Syst Rev. 2011;(11):CD004022. doi:10.1002/14651858
  3. Sacks FM, Svetkey LP, Vollmer WM, et al; DASH-Sodium Collaborative Research Group. Effects on blood pressure of reduced dietary sodium and the Dietary Approaches to Stop Hypertension (DASH) diet. N Engl J Med. 2001;344(1):3-10. doi:10.1056/NEJM200101043440101
  4. Neal B, Wu Y, Feng X, et al. Effect of salt substitution on cardiovascular events and death. N Eng J Med. 2021;385(12);1067-1077. doi:10.1056/NEJMoa2105675