the effects of other electrolytes), or through pathways in addition to blood pressure. The committee sought to synthesize these potential associations. The committee’s approach to assessing the evidence focused on new data about the health effects of sodium intake on measures of health outcomes, rather than on effects mediated through an intermediate marker, namely blood pressure (see Figure D-1 in Appendix D).
The committee’s assessment of the evidence reviewed was guided by a number of factors. These included the study design, the quantitative measures of dietary sodium intake and confounder adjustment, as well as the number and consistency of relevant studies available. Assessing the impact of sodium intake on health outcomes was complicated by variability in the types and quality of measures used in observational studies, so that measures could not be reliably calibrated across studies. These measures also were difficult to assess in comparison to sodium intake in clinical trials. It was the consensus of the committee that the lack of consistency among studies in the methods used for defining sodium intakes at both high and low ends of the range of typical intakes among various population groups precluded deriving a numerical definition for high and low intakes in its findings and conclusions. Likewise, the extreme variability in intake levels between and among population groups precluded the committee from establishing a “healthy” intake range. The committee could consider sodium intake levels only within the context of each individual study.
The evidence for an effect of sodium intake on health outcomes reviewed by the committee included a broad range of population groups and methodological approaches. All of the evidence on the health outcomes related to CVD, stroke, and mortality was observational, mostly prospective cohort studies, whereas the evidence on health outcomes related to heart failure included randomized clinical trials (RCTs). Although the committee considered using a meta-analysis to assess the evidence, this approach was deemed inappropriate for this review because of the marked heterogeneity among the reviewed studies, particularly with respect to variations in measuring sodium intake and adjusting for confounders. For the same reason, the committee did not use a rating system to evaluate individual studies. Instead, studies were reviewed and assessed on an individual basis, and the committee considered the evidence on associations between sodium intake and health outcomes in its totality.
In evaluating each study, the committee considered RCTs a higher-quality study design for determining the effect of sodium on health outcomes than were observational studies. Well-executed cohort studies were considered more important for suggesting associations between dietary intake and health outcomes than were case-control studies because of the potential for bias in dietary assessment of sodium intake with the case-control study design. Finally, cross-sectional studies were included as an