Sodium Reduction Study Spotlight Take-Away with Chef Dr. Mike

by Michael S. Fenster, MD

Effect of Dietary Sodium on Blood Pressure: A Crossover Trial

“In an investigation, details matter.”
~Jack Reacher

Considering that all well-done studies are forms of investigation, the details matter, especially given that complex and subtle findings are often transformed into short soundbites to grab a few moments of the ever-shortening news cycle and public attention span.

The push for dietary salt reduction suffered a serious setback in light of the findings of the SODIUM-HF trial (Study of Dietary Intervention under 100 mmol in Heart Failure) published in The Lancet in 2022.

“In that multicenter, international, randomized, controlled trial, patients with heart failure were randomly assigned to a strategy of dietary sodium restriction of less than 1500 mg per day or usual care without a sodium-restricted diet. The median dietary sodium intake, which was approximately 2200 mg per day at baseline in all patients, was reduced by 415 mg more per day in the low-sodium group than in the usual-care group. The incidence of death from any cause, cardiovascular-related hospitalizations, or cardiovascular-related emergency department visits (the composite primary outcome) did not differ [italics added] significantly between the two groups in the trial at 12 months.”[1]

Due to the lack of potent, meaningful findings in this and a number of other low-sodium dietary trials, a positive study would certainly help reinforce dietary sodium reduction.

If there were ever a group of people that should benefit from a low-salt diet, it would be those suffering from congestive heart failure. A prescription of reduced sodium intake has been, as noted by Dr. Salim Yusef of McMaster University, “entrenched as a recommendation for the prevention and treatment of many cardiovascular diseases.”

However, as Dr. Yusef continues to note, “many major professional societies in Canada, the United States, and Europe have stopped recommending strict dietary sodium restriction for patients with heart failure, given the lack of robust evidence supporting this historical practice.”

A recent study purports to provide evidence to the contrary by demonstrating a reduction of blood pressure through dietary sodium restriction.

The Study:

  • A crossover study of 213 individuals examining the effects on blood pressure in response to dietary sodium through a comparison of high-sodium versus low-sodium diets.

The Take-Away:

  • The study claims that the intervention is a difference between a high- or low-sodium diet.
  • The study examined 213 individuals aged 50 to 75 years, of whom 25 percent were normotensive. The participants served as their own controls under the crossover protocol.
  • The high-sodium diet was the participants’ “usual” diet plus the addition of 2200 mg of sodium from bouillon cubes.
  • The low-sodium diet contained 500 mg of sodium and was strictly pre-prepared and distributed to the participants.
  • Whilst on the low-sodium diet, participants could not consume any other items.
  • The study concluded that “dietary sodium reduction significantly lowers blood pressure in the majority of middle-aged to elderly adults.”

The Caveats:

  • The study highlights and indeed reports that the only intervention of consequence is a differential in the amount of daily sodium consumed; however, this is not the case:
    • The low-salt diet was strictly prepared in each site’s metabolic kitchen and supplied not only 500 mg of sodium but also 4500 mg of potassium each day.
    • The high salt diet was the participants’ usual diet, with the addition of two sodium bouillon packets, increasing the intake of sodium by approximately 2200 mg per day.
  • The participants’ high sodium diet contained an average of 5.48 g of sodium, while the average American’s diet contains an average of 3.61 g of sodium – a significant difference.
  • The average American’s daily potassium intake is 2.67 g per day, yielding an average daily sodium-to-potassium ratio of 1.35.
  • The participants’ sodium-to-potassium ratio on the high-salt diet was 3.2.
  • The participants’ sodium-to-potassium ratio of the low-sodium diet was 0.98.

This study highlights the dangers of using abbreviated soundbites to convey complex study results. Despite the inference that the only variable in the study was the sodium content of the diets, the study compared two completely different diets. A “usual” diet enhanced with additional sodium and a strictly controlled low-sodium diet that was also rich in potassium.

Potassium is known to be a vasodilator and has been shown to reduce blood pressure independently of sodium consumption. The sodium-to-potassium ratio has been shown to be a predictor of adverse outcomes independent of absolute amounts, with an increase in adverse events observed when the ratio exceeds one. The participants’ sodium-to-potassium ratio on the high-salt diet was 3.2. The participants’ sodium-to-potassium ratio of the low-sodium diet was 0.98.

The components of the participants’ “usual diet” remain undefined. There are over 25,000 known distinctive compounds found within various foods, many of which can have pleiotropic effects, including those on blood pressure. There is no accounting for the level of ultra-processing amongst the various foodstuffs, an independent variable associated with a 32 percent increased risk of developing hypertension.[2] Indeed, the addition of bouillon cubes to achieve the high sodium diet constitutes additional ultra-processed comestibles to the “usual” diet, with the average American’s diet consisting of more than 60 percent ultra-processed foods at baseline.

Finally, this study observed the effects over a one-week period. Acute ingestion of significant amounts of salt has been shown to increase blood pressure, but this can be quite a transitory effect over time in the setting of normal renal function. The study was also not designed to measure “hard” endpoints (e.g., death, heart attack, stroke, etc.) and assumes that any blood pressure changes achieved through such dietary means translate into measurable reductions in mortality and morbidity.

A lack of attention to detail coupled with assumptions is a volatile recipe. As Reacher also observed, “Frankenstein is The Doctor. They went after Frankenstein’s Monster. Details Matter.”

The Study:

Gupta DK, Lewis CE, Varady KA, et al. Effect of dietary sodium on blood pressure: a crossover trial. JAMA. Published online November 11, 2023. doi:10.1001/jama.2023.23651

Supplemental study data link

Additional Resources:

Cogswell ME, Loria CM, Terry AL, Zhao L, Wang CY, Chen TC, Wright JD, Pfeiffer CM, Merritt R, Moy CS, Appel LJ. Estimated 24-Hour Urinary Sodium and Potassium Excretion in US Adults. JAMA. 2018 Mar 27;319(12):1209-1220. doi: 10.1001/jama.2018.1156.

Ezekowitz JA, Colin-Ramirez E, Ross H, Escobedo J, Macdonald P, Troughton R, Saldarriaga C, Alemayehu W, McAlister FA, Arcand J, Atherton J, Doughty R, Gupta M, Howlett J, Jaffer S, Lavoie A, Lund M, Marwick T, McKelvie R, Moe G, Pandey AS, Porepa L, Rajda M, Rheault H, Singh J, Toma M, Virani S, Zieroth S; SODIUM-HF Investigators. Reduction of dietary sodium to less than 100 mmol in heart failure (SODIUM-HF): an international, open-label, randomised, controlled trial. Lancet. 2022 Apr 9;399(10333):1391-1400. doi: 10.1016/S0140-6736(22)00369-5.

Chang, LL. Dietary Sodium Restriction in Patients with Heart Failure. NEJM. 2023. 388 (17):1621-1623.https://www.nejm.org/doi/full/10.1056/NEJMclde2215283

NIH. (2022, June 2). Potassium Intakes and Status. Retrieved from NIH Fact Sheets: https://ods.od.nih.gov/factsheets/Potassium-healthProfessional/#:~:text=In%20adults%20age%2020%20and,2%2C449%20mg%20potassium%20per%20day.

Vitale, M., Costabile, G., Testa, R., D’Abbronzo, G., Nettore, I. C., Macchia, P. E., & Giacco, R. (2023). Ultra-Processed Foods and Human Health: A Systematic Review and Meta-Analysis of Prospective Cohort Studies. Advances in Nutrition, https://doi.org/10.1016/j.advnut.2023.09.009.


[1] (Chang, 2023)

[2] (Vitale, et al., 2023)

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