COMMITTEE TASK AND APPROACH
Against the backdrop of questions about sodium reduction in the population, the Centers for Disease Control and Prevention of the U.S. Department of Health and Human Services (HHS) asked the Institute of Medicine (IOM) to convene an expert committee to examine the designs, methodologies, and conclusions of this emerging evidence, as well as other reports published since the 2005 Dietary Reference Intake (DRI) report, Dietary Reference Intakes for Water, Sodium, Chloride, and Sulfate. Specifically, the committee was asked to review and assess the benefits and adverse outcomes (if any) of reducing sodium intake in the population, particularly in the range of 1,500 to 2,300 mg per day, with an emphasis on relevant subgroups. These subgroups include individuals with hypertension and prehypertension, those 51 years of age and older, African Americans, and those with diabetes, chronic kidney disease, and congestive heart failure (CHF). The committee also was asked to comment on the implications for population-based strategies to reduce sodium intake and to identify data and methods gaps and suggest ways to address them.
In approaching its task, the committee first conducted a broad search of the published literature through 2012 to identify relevant scientific publications on sodium and direct health outcomes. The committee was unable to identify studies published prior to 2003 that provided data on how the frequency of direct health outcomes was associated with changes in dietary sodium. Information also was gathered from a public workshop. The committee then developed a strategy to qualitatively assess each study identified as relevant from the search. Although an in-depth review was not conducted, the committee also considered evidence published since 2003 on associations between sodium intake and intermediate markers, particularly blood pressure. This additional evidence on the effect of sodium on blood pressure supported the findings and conclusions in the DRI report, the technical report from the 2010 Dietary Guidelines Advisory Committee (DGAC), and the recently released 2012 report from the World Health Organization, Guideline: Sodium Intake for Adults and Children.
Although blood pressure is a widely accepted surrogate marker, the scientific community continues to debate the use of other intermediate markers and biomarkers generally. Further, and in keeping with the systematic evidence review in the DGAC report, the effects of lowering sodium intake on blood pressure, as with other biomarkers, cannot always be disentangled from the effects of total dietary modification. For example, the committee’s review revealed that in a number of studies, the effects of dietary sodium on CVD outcomes sometimes persisted even after controlling for blood pressure. This suggests that associations between dietary sodium and risk of CVD may be mediated through interaction with other dietary factors (e.g.,