A Look at the Disputed Science on Salt: Is Lower Always Better?
Below is the scientific evidence questioning/contradicting recommendations that a “lower is better” recommendation on sodium is advisable for the general population.
At least five separate scientific teams published in major peer-reviewed journals, in addition to a 2013 review by the U.S. Institute of Medicine (National Academy of Sciences) all concluded that lowering salt below a moderate amount increased the risk of disease and death
The policy of “lower-is-better” is therefore clearly not evidence-based.
Population-wide policies must be backed by strong and consistent scientific evidence. That is not the case with salt.
Evidence on Salt
The following is a list of the evidence contradicting the current dietary recommendations that “lower is better’ for salt intake, followed by specific evidence looking at salt intake in type 2 diabetes, as well as further commentary pieces from various sources.
1. Sodium Intake in Populations: Assessment of Evidence. Institute of Medicine, National Academy of Sciences (2013)
“The committee also concludes that studies on health outcomes are inconsistent in quality and insufficient in quantity to determine that sodium intakes below 2,300 mg/ day either increase or decrease the risk of heart disease, stroke, or all-cause mortality in the general U.S. population.”
The report concludes that sodium intake below 2,300 mg/day may lead to adverse health outcomes in several “disease-specific populations,” including those with diabetes and pre-existing heart disease, a population that includes tens of millions of Americans.
2. Fatal and nonfatal outcomes, incidence of hypertension, and blood pressure changes in relation to urinary sodium excretion. Journal of the American Medical Association (2011). K. Stolarz-Skrzypek, T. Kuznetsova, L. Thijs, et al; European Project on Genes in Hypertension (EPOGH) Investigators.
“In this population-based cohort, systolic blood pressure, but not diastolic pressure, changes over time aligned with change in sodium excretion, but this association did not translate into a higher risk of hypertension or CVD complications. Lower sodium excretion was associated with higher CVD mortality…. Taken together, our current findings refute the estimates of computer models of lives saved and health care costs reduced with lower salt intake. They do also not support the current recommendations of a generalized and indiscriminate reduction of salt intake at the population level. However, they do not negate the blood pressure−lowering effects of a dietary salt reduction in hypertensive patients”
3. Compared with usual sodium intake, low- and excessive-sodium diets are associated with increased mortality: a meta-analysis. Journal of Hypertension (2014). N. Graudal, G. Jürgens, B. Baslund, M.H. Alderman.
“Our study extends the IOM report by identifying a specific range of sodium intake (2,645–4,945 mg) associated with the most favorable health outcomes, within which variation in sodium intake is not associated with variation in mortality.”
“Both low sodium intakes and high sodium intakes are associated with increased mortality, consistent with a U-shaped association between sodium intake and health outcomes.”
4. Urinary sodium and potassium excretion, mortality, and cardiovascular events. New England Journal of Medicine (2014). M. O'Donnell, McMaster University, A. Mente, S. Rangarajan, et al, for the PURE investigators.
“In this study in which sodium intake was estimated on the basis of measured urinary excretion, an estimated sodium intake between 3 g per day and 6 g per day was associated with a lower risk of death and cardiovascular events than was either a higher or lower estimated level of intake. As compared with an estimated potassium excretion that was less than 1.50 g per day, higher potassium excretion was associated with a lower risk of death and cardiovascular events.
Updated Findings: Associations of urinary sodium excretion with cardiovascular events in individuals with and without hypertension: a pooled analysis of data from four studies. The Lancet (2016). A. Mente, Department of Clinical Epidemiology and Biostatistics, McMaster University, M. O’Donnell, S. Rangarajan, et al, for the PURE, EPIDREAM, and ONTARGET / TRANSCEND Investigators.
“Compared with moderate sodium intake, high sodium intake is associated with an increased risk of cardiovascular events and death in hypertensive populations (no association in normotensive population), while the association of low sodium intake with increased risk of cardiovascular events and death is observed in those with or without hypertension. These data suggest that lowering sodium intake is best targeted at populations with hypertension who consume high sodium diets.”
5. The technical report on sodium intake and cardiovascular disease in low- and middle-income countries by the joint working group of the World Heart Federation, the European Society of Hypertension and the European Public Health Association. European Heart Journal (2017). G. Mancia, University of Milano-Biccoca, S. Oparil P.K. Whelton, et al.
“Prospective cohort studies have identified the optimal range of sodium intake to reside in the moderate range (3–5 g/day), where the risk of cardiovascular disease and death is lowest. Therefore, there is consistent evidence from clinical trials and observational studies to support reducing sodium intake to less than 5 g/day in populations, but inconsistent evidence for further reductions below a moderate intake range (3–5 g/day).”
Quote from paper: “Sodium is an essential nutrient. This implies that there must be a ‘U’-shaped relationship between dietary sodium intake and cardiovascular events, but there is no consensus of where the minimum risks lies.”
6. Association Between Sodium Excretion and Cardiovascular Disease and Mortality in the Elderly: A Cohort Study. The Journal of Post-Acute and Long-term Care Medicine (2018) Diana Lelli, MD, Raffaele Antonelli-Incalzi, MD, Stefania Bandinelli, MD, Luigi Ferrucci, MD, PhD, Claudio Pedone, MD, PhD, MPH
Conclusion: "Reduced sodium excretion is associated with increased mortality in a sample of community-dwelling older people, especially among the frail participants. High levels of sodium excretion are not associated with adverse outcomes in this population; therefore, sodium restriction might not be beneficial in older people."
Editorial by The New England Journal of Medicine (2014), commenting on evidence to date
“In the absence of such a [randomized, controlled clinical] trial, the results argue against reduction of dietary sodium as an isolated public health recommendation.”
Editorial by The Lancet - Salt—too much or too little? (2016)
“There is no argument other than “excessive salt in the diet raises blood pressure”, and that strategies to reduce salt in individuals with hypertension prevent the cardiovascular consequences of the disease. However, the corollary that reducing sodium intake across populations will be beneficial to all, has been challenged with the assertion that doing so might indeed be harmful.”
International Experts Call Salt Guidelines Far Too Restrictive. Cardiobrief (2017), Larry Husten
Type 2 Diabetes
In patients with type 2 diabetes, two studies have observed increased all-cause and cardiovascular mortality associated with low-sodium intake.
1. Dietary Salt Intake and Mortality in Patients With Type 2 Diabetes. Diabetes Care (2011). E.I. Ekinci, S. Clarke, M.C. Thomas, et al.
“In patients with type 2 diabetes, lower 24-h urinary sodium excretion was paradoxically associated with increased all-cause and cardiovascular mortality.”
2. Urinary Sodium Concentration Is an Independent Predictor of All-Cause and Cardiovascular Mortality in a Type 2 Diabetes Cohort Population. Journal of Diabetes Research, 2017. P-J. Saulnier, CHU de Poitiers, Centre d’Investigation Clinique, Université de Poitiers, UFR Médecine Pharmacie, Inserm, Poitiers, E. Gand, S. Ragot et al, and SURDIAGENE Study group.
“Urinary sodium independently predicted all-cause and cardiovascular mortality. An increase of one standard deviation of urinary sodium was associated with a decrease of 21% of all-cause mortality and 22% of cardiovascular mortality.”
Additional commentary on the salt debate
Congressman Andy Harris, MD, sends a letter (June 30, 2016) to FDA Commissioner Robert Califf to express “strong disappointment and objection” to the FDA’s new voluntary sodium limits in food. Harris asks the Commissioner to explain misrepresentation of the IOM 2013 study on sodium.
Could 95 Percent of the World’s People Be Wrong About Salt? Washington Post (2015), Peter Whoriskey, staff writer.
The Salt Libel - Wall Street Journal (2014)
The Population Risks of Dietary Salt Excess are Exaggerated. The Canadian Journal of Cardiology (2014). A. Mente, Population Health Research Institute, McMaster University, M.J. O’Donnell, S. Yusuf.
“Policy positions on salt consumption (based largely on the association of sodium and blood pressure [BP]) has remained unchanged since the 1970s, until recently. However, this is beginning to change as new evidence emerges. The evidence supports a strong association of sodium with BP and cardiovascular disease events in hypertensive individuals, the elderly, and those who consume > 6 g/d of sodium. However, there is no association of sodium with clinical events at 3 to 6 g/day and a paradoxical higher rate of events at < 3 g/day. Therefore, until new evidence emerges, the optimal range of sodium consumption should be considered to be between 3 and 6 g/d. Population-wide sodium reduction is not justified in countries such as Canada.”