However, in the case of blood pressure, the recent report on biomarkers (IOM, 2010) points to its wide acceptance as a surrogate marker and to the recent evidence attributing 35 percent of myocardial infarction and stroke events, 49 percent of heart failure episodes, and 24 percent of premature deaths to high blood pressure (Lawes et al., 2008). Nevertheless, the committee recognizes that cardiovascular effects do not occur only as a result of blood pressure. For example, and as described in the 2010 IOM report, it is known that different classes of drugs can have multiple cardiovascular outcomes but not all of them are a result of their blood pressure lowering effects. For example, despite their effects on blood pressure, alpha blockers have been shown to have a higher risk of heart failure compared to diuretics (ALLHAT Collaborative Research Group, 2000). The committee also recognizes that, in addition to blood pressure effects, diets modified in sodium may execute their effects on health outcomes through other factors, including other dietary constituents. The committee did not address questions related to such potential additional mechanisms because such questions were not part of its statement of task.
The committee’s assessment of the evidence reviewed was influenced by a number of factors. These included the variability in methodological approaches used to evaluate relationships between sodium intake and risk of health outcomes, study design, limitations in the quantitative measures of both dietary intake and urinary excretion of sodium, confounder adjustment, and the number of relevant studies available. Assessing the impact of sodium intake on health outcomes was further complicated by wide variability in intake ranges among studies. For example, in the studies reviewed, high sodium intake levels for examining associations with health outcomes ranged from about 2,700 to more than 10,000 mg per day. The lack of consistency between studies in defining sodium intakes at both high and low ends of the range of typical intakes among various population groups meant that the committee could not derive a numerical definition for high or low intakes in its findings and conclusions. Rather, it could consider sodium intake levels only within the context of an individual study. Thus, in its findings and conclusions, the committee’s use of “high” or “low” sodium intake indicates levels in the ranges described in the evidence reviewed.
Sources of Information
The committee obtained data and information for its conclusions from several sources. The main source of information came from a review of the evidence in the scientific literature from 2003 through 2012. For this review, scientific literature searches were conducted by the study staff in