The study involved patients with heart failure; people felt particularly sensitive to the presence of extra salt. Heart failure comes in a variety of forms, but in its heart (pun intended?) the pumping ability fails and fluid backs up into the lungs causing increased shortness of breath or into our veins causing swelling in the legs. Physiologically, the addition of salt increases our blood volume, further aggravating the failure of the heart as a pump, worsening shortness of breath, reduced mobility and swelling in the legs.
The American Heart Association recommends no more than 2.3 g of salt per day, ideally 1.5 g. The typical diet is closer to 3.5g. This spawned a cottage industry of listicles, including the Salty Six and 30 Foods with High Salt and even salt consumption legislation permitted by people living in nursing homes.
The study was randomized but open label; participants knew whether they were sodium restricted or not. Approximately 800 participants, optimally managed for heart failure, were randomized to receive treatment as usual versus salt restriction of 1500 mg. Patients were classified as NYHA 2 or 3 – mildly to moderately disabled for physical activity but still comfortable at rest. Average age of 66, about a third female, and the study lasted a year before being prematurely terminated by what else, COVID.
- “At 12 months, dietary sodium intake was 1658 mg in the low sodium diet group versus 2073 mg in the usual care group.”
- “The primary outcome, all-cause mortality or cardiovascular ER visit/hospitalization at 12 months, occurred in 15% of the low sodium group versus 17% of the usual care group.”
- “All-cause mortality at 12 months: 6% in low sodium group versus 4% in usual care group.”
- “The Difference in Kansas City Cardiomyopathy Questionnaire (KCCC) Adjusted Mean  the global summary score at 12 months was 3.38 points higher in the low sodium group compared to the usual care group. This questionnaire has a scale of 100 points, representing a change of 3%.
- “The difference in the mean adjusted 6-minute walk test at 12 months was 6.6 minutes greater in the low sodium group compared to the usual care group.”
“In ambulatory patients with heart failure, dietary intervention to reduce sodium intake did not reduce clinical events.”
Only sodium intake and subjective KCCC score were statistically significant. Significant sodium restriction did not improve patients’ day-to-day health or outcomes in mild to moderate congestive heart failure. And those roughly 6.2 million patients are theoretically more susceptible to the impact of salt intake than the roughly 344 million of us without CHF. (Admittedly, I’m playing a little fast and loose with these numbers. This doesn’t take into account people with kidney failure where sodium intake is a much bigger issue or other conditions, but the number of advised to limit sodium is much higher than those at risk.)
In an open-label study and therefore with a bias in self-reporting, sodium restriction detected only a small subjective difference with sodium restriction and no net physical benefit. Many studies on the impact of dietary salt on hypertension date from the late 1980s and 1990s – it may be time to reevaluate these findings, especially in light of the fact that some people are more susceptible salt than others. A call for such a study was launched in 2018 and remains unsatisfied.
Source: Study of Dietary Intervention Under 100 mmol in Heart Failure – SODIUM-HF A presentation at the American College of Cardiology (ACC)
Subsequently published as Reduction of dietary sodium to less than 100 mmol in heart failure (SODIUM-HF): an international, open-label, randomized, controlled trial Lancet DOI: 10.1016/S0140-6736(22)00369-5
Note: The Lancet article is behind a paywall, and my reporting is based on material available in the ACC presentation.