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 worldwide, 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 a moderate amount (3-5g daily) of sodium is an optimal, population-wide recommendation. Below this, an increased risk of disease and death is seen. Therefore, the proposed front-of-package warnings on salt for all Canadians could very well increase rates of death and disease among its citizens.
The policy of “lower-is-better” for all 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.
Scientific evidence, in chronological order:
Institute of Medicine, National Academy of Sciences (2013)
“Evidence from studies on direct health outcomes is inconsistent and insufficient to conclude that lowering sodium intake below 2,300 mg/day either increases or decreases risk of CVD outcomes (including stroke and CVD mortality) 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.
Journal of the American Medical Association (2011)
Stolarz-Skrzypek, T. Kuznetsova, L. Thijs, et al; European Project on Genes in Hypertension (EPOGH) Investigators.
“An estimated sodium intake between 3g per day and 6 g per day was associated with a lower risk of death and cardiovascular events than either a higher or lower estimated level of sodium intake. As compared with an estimated potassium excretion of less than 1.50 g per day, higher potassium excretion was associated with a reduction in the risk of the composite outcome.”
Journal of Hypertension (2014) Graudal, G. Jürgens, B. Baslund, M.H. Alderman.
“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.”
New England Journal of Medicine (2014O’Donnell, McMaster University , A. Mente, S. Rangarajan, et al, for the PURE investigators.
“Compared with moderate sodium intake, high sodium intake [>7g/day] 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 [<3g/day] 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.”
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.”
Mente, Department of Clinical Epidemiology and Biostatistics, McMaster University, M. O’Donnell, S. Rangarajan, et al, for the PURE, EPIDREAM, and ONTARGET/TRANSCEND Investigators.
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.
(6) “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)
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.”
Type 2 Diabetes:
In patients with type 2 diabetes, two studies have observed increased all-cause and cardiovascular mortality associated with low-sodium intake.
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.” [NT2] “An increase of one standard deviation of U-Na was associated with a decrease of 21% of all-cause mortality and 22% of cardiovascular mortality”
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.
Additional commentary on the salt debate
“Salt Intake and Cardiovascular Disease: Why are the Data Inconsistent?” European Heart Journal (2013)
O’Donnell, Department of Medicine (M.O.D., S.Y.), and Department of Clinical Epidemiology and Biostatistics (A.M.), Population Health Research Institute, Hamilton Health Sciences, McMaster University, A. Mente, A. Smyth, S. Yusuf.
The Canadian Journal of Cardiology (2014)
Mente, Population Health Research Institute, McMaster University, M.J. O’Donnell, S. Yusuf.
“The Salt Libel”
Wall Street Journal (2014)
“Could 95 Percent of the World’s People Be Wrong About Salt?”
Washington Post (2015)
Peter Whoriskey, staff writer.
Circulation Research (2015)
O’Donnell, Department of Medicine (M.O.D., S.Y.), and Department of Clinical Epidemiology and Biostatistics (A.M.), Population Health Research Institute, Hamilton Health Sciences, McMaster University, A. Mente, S. Yusuf.
“It is assumed that the blood pressure-lowering effects of reducing sodium intake to low levels will result in large reductions in cardiovascular disease globally. However, current evidence from prospective cohort studies suggests a J-shaped association between sodium intake and cardiovascular events, based on studies from >300 000 people, and suggests that the lowest risk of cardiovascular events and death occurs in populations consuming an average sodium intake range (3-5 g/d).”
Congressional Concern Regarding the U.S. Sodium Guideline
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.
This document prepared by Nina Teicholz, science journalist, author, and Executive Director of the Nutrition Coalition.