Americans consume more sodium than is recommended. Current estimates say that the average American consumes about 3,400 milligrams (mg) per day, or about 1.5 times the 2,300 mg that is recommended for healthy individuals. Reducing the amount of sodium in the American diet is a primary focus for a key public health initiative to lower blood pressure as a means to reduce risk for cardiovascular disease (CVD) across the population. Emerging evidence, however, suggests that low sodium intakes may increase health risks, especially in certain populations.
With all of this in mind, the Centers for Disease Control and Prevention (CDC) of the U.S. Department of Health and Human Services (HHS) recently commissioned the Institute of Medicine (IOM) to form an expert committee to compile a report assessing whether sodium reduction increases the risk of adverse health outcomes for the general U.S. population as well as for “at-risk” population subgroups: individuals with hypertension or pre-hypertension, those 51 years of age and older, African Americans and those with diabetes, chronic kidney disease and congestive heart failure. To complete this task, the IOM committee was asked to review the literature published since 2003, including a range of sodium intake levels between 1,500 mg and 2,300 mg. The Committee was not asked to recommend a specific range of sodium intake for any population subgroups of assess intermediate end points such as blood pressure.
Released on May 14, 2013, the IOM report, Sodium Intake in Populations: Assessment of Evidence, compiles the most current evidence regarding sodium and cardiovascular disease, stroke and mortality. The literature search included 38 scientific studies with 34 being observational in design and four randomized clinical control trials. Major findings and conclusions in the report differ between the general population and the aforementioned subgroups.
For the general population, the committee came to two conclusions. First, they found “a positive relationship between higher levels of sodium intake and risk of CVD. This evidence is consistent with existing evidence on blood pressure as a surrogate indicator of CVD risk.”
Second, regarding the range of sodium consumption that the committee was asked to consider, the committee “determined that evidence from studies on direct health outcomes is inconsistent and insufficient to conclude that lowering sodium intakes below 2,300 mg per day either increases or decreases risk of CVD outcomes (including stroke and CVD mortality) or all-cause mortality in the general U.S. population.”
For specific subgroups of the population, two conclusions were also reached. First, the committee stated “the available evidence suggests that low sodium intakes may lead to higher risk of adverse events in mid- to late-stage CHF [Congestive Heart Failure] patients with reduced ejection fraction and who are receiving aggressive therapeutic regimens.” It is noted, that evidence for this is based on studies conducted outside the US and thus different clinical protocols were used. The report calls for more research utilizing “standard US clinical practice.” Additionally, according to an article written by three members of the IOM committee published online on June 6, 2013 in the Journal of the American Medical Association, “due to allegations of duplicate publication in 2 of these trials, a meta-analysis including them was recently retracted, after the IOM report’s completion. Another recently published small randomized trial involving patients with acute decompensated HF showed no benefit on weight or clinical stability from a combination of sodium and fluid restriction.”
Second, “the committee concluded that the evidence on direct health outcomes does not support recommendations to lower sodium intake within these subgroups to, or even below, 1,500 mg per day.”
The IOM committee was not asked to further examine the relationship between dietary sodium intake and blood pressure as this has been studied extensively with a substantial body of evidence linking excessive sodium intake to high blood pressure for some population groups. From this relationship and this research, the 2010 Dietary Guidelines for Americans recommended that the general U.S. population consume less than 2,300 mg of sodium per day; however, for large subgroups of the population who are at a higher risk, specifically mentioned as African Americans, people over 51 years of age, and people with hypertension, diabetes, or chronic kidney disease, the Guidelines recommend reducing sodium intake to 1,500 mg per day.
This IOM report goes beyond sodium’s impact on blood pressure to explore the potential for both positive and negative health outcomes with low sodium intake. Evolving research has questioned the role of low sodium intake in increasing risk of heart disease and stroke due to its effect on blood lipids and insulin resistance. While the report does find sufficient evidence to support lowering excessive sodium intake population-wide, the report does not find enough available evidence to support lowering dietary sodium recommendations to 1,500 mg per day for the entire population.
Furthermore, according to the expert’s report, there is no evidence to support treating population subgroups differently from the general population or to indicate a benefit from lowering sodium below the 2,300 mg per day that is currently recommended—this is a marked difference from the current 2010 Dietary Guidelines for Americans. The IOM report does state, however, that there are limitations in the available data and suggest that a “healthy” sodium intake range could be addressed in future clinical studies.
This IOM report may represent a shift in the way sodium intake amounts are viewed. In recent times, a focus on the relationship between high sodium intake and elevated blood pressure has driven key public health efforts to substantially reduce sodium intake across the population. In addition to supporting the effort to reduce American consumption from current levels (3,400 mg), the IOM report submits additional evidence on the associated health outcomes of such reductions. Until now, most attention has been paid to the positive health benefits of low sodium intakes and relatively little attention to a small but growing body of research showing the potential for adverse health outcomes at low sodium intakes. Given the significant impact of sodium recommendations on policy implementation, this newly published IOM review of the existing evidence is a critical step in ensuring science-driven health policy.