clinical outcomes identified by the committee was observational, consisting largely of prospective cohort studies. The committee also found important limitations associated with the quantitative measures of sodium intake (see Chapters 2 and 4) and recognized the potential for spurious findings related to incorrect measurement and reverse causality. Specifically, in some studies, low sodium intakes apparently appeared to show an association with risk of disease, when, in fact, the relationship may have been that the disease itself led to low or incomplete measures of sodium among those with preexisting disease (see Chapter 4).
Assessing the impact of sodium intake on health outcomes also was complicated by variability in the types and quality of measures used, so that measures could not be reliably calibrated across studies. 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. Rather, it could consider sodium intake levels only within the context of each individual study. Likewise, the extreme variability in intake levels between and among population groups precluded the committee from establishing a “healthy” intake range.
Recognizing the limitations of the available evidence, the committee found no consistent evidence to support an association between sodium intake and either a beneficial or adverse effect on health outcomes other than CVD outcomes (including stroke and CVD mortality) and all-cause mortality. Some evidence suggested that decreasing sodium intake could possibly reduce the risk of gastric cancer. However, the evidence was too limited to conclude the converse—that higher sodium intake could possibly increase the risk of gastric cancer. Interpreting these findings was particularly challenging because most gastric cancer studies were conducted outside the United States in populations consuming much higher levels of sodium than those consumed in this country. Thus, the committee focused its findings and conclusions on evidence for associations between sodium intake and risk of CVD-related events and mortality.