By Michael H. Crawford, MD, Editor
SYNOPSIS: A study of a low-sodium diet for chronic, stable heart failure patients after one year showed no difference in hard clinical outcomes, but the degree of sodium restriction was modest.
SOURCE: Ezekowitz JA, Colin-Ramirez E, Ross H, et al. Reduction of dietary sodium to less than 100 mmol in heart failure (SODIUM-HF): An international, open-label, randomized, controlled trial. Lancet 2022;399:1391-1400.
This trial was designed to test the effects of dietary sodium restriction to under 100 mmol on clinical outcomes in chronic heart failure (HF) patients using a pragmatic, open-label design. The work was conducted in 26 centers in six countries.
HF was defined locally. There was no ejection fraction (EF) or natriuretic peptide criteria for admission, but patients with a dietary sodium intake of < 1,500 mg/day, a serum sodium recording less than 130 mmol/L, an estimated glomerular filtration rate of < 20mL/min/1.73 m2, on hemodialysis, or admitted to the hospital for a cardiovascular (CV) cause in the last month were excluded. Patients were randomly assigned to usual care or a < 1,500 mg of sodium/day diet. Study group assignment was known to the participants and their physicians, but endpoints were adjudicated by an events committee masked to group assignment. All patients were given suggested menus for a CV disease diet, which included general advice to restrict sodium, but the low-sodium diet group was given behavioral counseling to achieve the low sodium goal.
The intervention lasted 12 months, and the patients were followed for an additional 12 months. The control group recorded two follow-up visits — at six months and at 12 months. The test group logged two additional visits — three months and nine months. The purpose of follow-up visits was to reinforce the low-sodium diet. In addition to clinical information, clinicians assessed dietary sodium intake.
The primary composite endpoint included CV hospitalization or ED visits and all-cause death at 12 months. Secondary outcomes included the individual primary outcomes, plus quality of life (QOL), six-minute walk distance, and New York Heart Association (NYHA) functional class. The 806 patients enrolled from 2014 through 2020 were 81% of the planned 992 patients; the trial ended early for several reasons, including the dawn of the COVID-19 pandemic. The median age of the study population was 67 years, and 33% were women.
Median EF was 36%, and median brain natriuretic peptide (BNP) in 263 patients was 197 pg/mL. In the usual care group, median sodium intake at 12 months was 2,073 mg/day. In the low sodium group, median intake was 1,658 mg/day, which was 28% lower than at enrollment. The median difference of 415 mg/day was significant (P < 0.0001). Follow up at 12 months was 98%. The primary outcome occurred in 15% of the low-sodium diet group and 17% of the usual care group (HR, 0.89; 95% CI, 0.63-1.26; P = 0.53). The only secondary outcome that was significantly different was the low sodium group had a greater chance of improving by one NYHA class than the control group (OR, 0.59; 95% CI, 0.40-0.86; P = 0.0061). Also, researchers did not detect any adverse events from a low-sodium diet. The authors concluded dietary sodium reduction in ambulatory patients with chronic HF did not prevent clinical outcomes at one year.
COMMENTARY
This trial included a large cohort, and the follow-up period was long — yet the authors did not see differences in the primary outcome at 12 months. Perhaps an even longer follow-up period would have made a difference — this trial ended early because of so few events (and the outbreak of COVID-19). The investigators predicted a 25% primary event rate in the control group, but it was only 17%. This may be because the sodium intake of the control group was about 2,000 mg/day, which is considered a low-sodium diet vs. what normal individuals consume (probably between 4,000 mg/day and 8,000 mg/day). Thus, cutting about 400 mg/day, which happened in this study, may not have been enough to make a difference in outcomes. Also, the control group was told to eat a low-sodium diet without any specific instructions on how to do this. They did experience a 4% drop in sodium intake at one year, but this was considerably less than the treatment groups. Perhaps if the control group recorded a higher sodium intake, more differences in outcomes would have been seen. In addition, three-quarters of the patients were in NYHA class II. Such patients experience a lower event rate than those in higher classes. Recruiting more NYHA class III patients may have augmented the difference in outcomes.
There were strengths to this study. In addition to the large cohort and long follow-up period, researchers recruited a diverse patient population with markedly different diets and food cultures. This is one reason why prepared foods were not used in this study, but rather individualized menu suggestions based on the local cuisine. Patients all experienced chronic HF for at least one year and were at least one month out from any hospitalizations. Also, subjects were on excellent pharmacologic therapy for HF.
Still, there were weaknesses. Urinary sodium excretion is the gold standard for dietary sodium intake, but was not feasible in this study, nor was it feasible to measure BNP in everyone or conduct serial echocardiograms. Also, no fluid or calorie intake was prescribed, but these parameters did not change during the study. Physicians and patients were not blinded to the study group, which could have biased some subjective measures, such as quality of life and NYHA class. However, a blinded event committee adjudicated the outcomes.
The main problem with this otherwise well-conducted study is chronic HF patients have received the message from clinicians: reduce salt intake. Most clinicians likely would be happy if patients were at 2,000 mg of sodium/day. It takes a big effort to move below this threshold; in this study, the authors reported they did not reach their target of less than 1,500 mg/day in most patients in the low sodium group (median = 1,658 mg/day).
A study of a low-sodium diet for chronic, stable heart failure patients after one year showed no difference in hard clinical outcomes, but the degree of sodium restriction was modest.
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