Greater scientific rigour required for all dietary sodium studies related to health outcomes.
The recent article by Jun and Neal (1), "Low dietary sodium in heart failure: a need for scientific rigour," calls for greater consistency and attention in one outcome related to salt intake. The Salt Institute is in complete agreement with their call for greater scientific rigour and believes, in the interests of public health, that this should be extended to all health outcomes related to dietary sodium intake. While blood pressure is one of several important surrogate measurements for cardiovascular disease, it is not a key measure for many other health outcomes. Overall health outcomes related to essential nutrients are generally described by their dose response and the J- or U-shaped curve (Bertrand's Rule) is a common characteristic of virtually all micro- nutrients, including sodium. Unfortunately, the available data for sodium is erratic, contradictory and continually open to subjective interpretation.
It is unfortunate that Jun and Neal neglected to including a reference to the recent CDC-sponsored IOM Committee on the Consequences of Sodium Reduction in Populations report (1) which found no evidence for benefit and some evidence suggesting risk of adverse health outcomes associated with the sodium intake levels recommended by the Dietary Guidelines (1,500 to 2,300 mg/day) among those with diabetes, kidney disease, or CVD. The report further stated that evidence on both the benefit and harm is not strong enough to indicate that subgroups should be treated differently than the general U.S. population and that direct health outcomes do not support recommendations to lower sodium intake within these subgroups down to or even below 1,500 mg/day. Obviously, the practice of relying on a single surrogate health measure has limitations resulting in questionable Dietary Guidelines that have been in effect for a decade.
Of critical significance, on page 20 (Section 1-2) of this new IOM report, the Committee on the Consequences of Sodium Reduction in Populations specificallyquoted a statement from the original Dietary Reference Intakes stating that the requirements for sodium were not derived from actual evidence, but were arbitrarily set. "In establishing DRI values for sodium, the Panel on Dietary Reference Intakes for Electrolytes and Water (IOM, 2005) found insufficient evidence to derive Recommended Dietary Allowances. Instead Adequate Intakes (AIs) were set for all life stage and gender groups." This new report, along with numerous Cochrane Collaboration and other meta-analyses underscore the fact that the evidence base is not currently at a level of quality that can be considered scientifically acceptable. The unrestricted, universal acceptance of these recommendations, despite their lack of an acceptable base of scientific evidence, makes it all the more important that greater rigour be applied, before they can be considered valid.
Morton Satin Salt Institute Alexandria, VA
1) Min Jun, Bruce Neal, Low dietary sodium in heart failure: a need for scientific rigour Heart Online First, published on June 1, 2013 as 10.1136/heartjnl-2012-303266. 2) IOM (Institute of Medicine). (2013). Sodium intake in populations: Assessment of evidence. Washington, DC: The National Academies Press. Accessed at http://www.iom.edu/Reports/2013/Sodium-Intake -in-Populations-Assessment-of-Evidence.aspx on 2/6/2013.
Conflict of Interest:
Morton Satin is employed by the Salt Institute, Alexandria, VA 22314, USA