I.O.M.: No benefit in sharp sodium cuts

by Eric Schroeder
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WASHINGTON — New research from the Institute of Medicine has found no evidence to support recommendations to significantly lower sodium intake below 2,300 mg per day for the general U.S. population or below 1,500 mg per day within certain subgroups. Currently, American adults consume an average of 3,400 mg per day, the I.O.M. said.

The findings fly in the face of the 2010 Dietary Guidelines for Americans, which include a goal of reducing dietary sodium intake to less than 2,300 mg per day for the general population, and further reducing intake to 1,500 mg per day among certain large population subgroups who may be at higher risk, including African Americans, people 51 years of age and older, and people who have hypertension, diabetes, or chronic kidney disease.

The report, “Sodium intake in populations: Assessment of evidence,” was conducted by the I.O.M. at the request of the Centers for Disease Control and Prevention and focused on recent studies that have looked at the direct effects of sodium on health outcomes. The I.O.M. was asked to review and assess the study designs, methodological approaches, and conclusions about studies on sodium intake linked to direct health outcomes.

In general, the I.O.M. found that the new studies “are not consistent in their methodological approaches to measuring sodium intake and that they have many limitations related to the quality of those measures and the quantity of available evidence assessing sodium intake and health outcomes.”

Limitations cited by the I.O.M. were over- or underreporting intake levels and incomplete collection of urine samples, as well as variability in the way the data were collected.

Despite the limitations, the I.O.M. concluded that the evidence supports a positive relationship between higher levels of sodium intake and risk of cardiovascular disease.

“This is consistent with existing evidence on blood pressure as a surrogate indicator of C.V.D. and stroke risk for the general population,” the I.O.M. said. The I.O.M. also concluded that studies on health outcomes are “inconsistent in quality” and “insufficient in quantity” to determine that sodium intakes below 2,300 mg per day either increase or decrease the risk of heart disease, stroke, or all-cause mortality in the general U.S. population.

For population subgroups who may be at higher risk, including African Americans, people 51 years of age and older, and people who have hypertension, diabetes, or chronic kidney disease, some studies have indicated that low sodium intake may lead to greater risk of adverse health effects in patients who have a diagnosis of moderate or severe congestive heart failure and are receiving certain aggressive therapeutic treatments. In its research, the I.O.M. found no evidence for benefit and some evidence suggesting risk of adverse health outcomes associated with sodium intake levels in ranges approximately 1,500 mg to 2,300 mg per day among those with diabetes, kidney disease and cardiovascular disease.

Furthermore, the committee said the evidence on both the benefit and harm of reducing sodium levels below 2,300 mg is not enough to indicate that the population subgroups should be treated any differently than the general U.S. population.

“The committee concludes that more randomized controlled trials will be needed, as these represent the highest quality study design for determining the effect of sodium on health outcomes,” the I.O.M. said. “Clinical trials might focus on examining the effects of a range of sodium levels on risk of cardiovascular events, stroke, and mortality among patients in controlled environments. This may be more feasible among individuals as part of natural experiments, such as those in other countries where policies affecting sodium consumption are in effect. Such trials may be especially important among higher-risk subgroups, including African Americans and adults 51 years of age and older, because less rigorous observational studies in these populations may be more prone to errors and provide less robust results.

“The committee also identifies a need for studies to collect and re-analyze data from existing clinical trials that were designed to evaluate sodium and health, as well as data during extended follow-up periods after the completion of a clinical trial to identify health outcomes.”

The I.O.M. was not asked to specify an optimal amount of sodium and did not provide any recommendations about how much people should consume.

The American Heart Association, which recommends that all Americans consume no more than 1,500 mg a day of sodium, said the new report is “incomplete” in its assessment of sodium’s impact on health “because it does not focus its examinations on scientific evidence that links excess consumption and high blood pressure.”

“While the American Heart Association commends the I.O.M. for taking on the challenging topic of sodium consumption, we disagree with key conclusions,” said Nancy Brown, chief executive officer of the A.H.A. “The report is missing a critical component — a comprehensive review of well-established evidence which links too much sodium to high blood pressure and heart disease.”

On the other side of the issue, The Salt Institute, an Alexandria, Va.-based non-profit trade association dedicated to advancing the benefits of salt, applauded the I.O.M.’s findings.

“We are pleased to see that the I.O.M. report has recognized that lowering sodium intake too much may actually increase a person’s risk of some health problems,” said Lori Roman, president of the Salt Institute. “I.O.M.’s recommendation that more study is needed is a positive first step toward a more objective dialog about the complex effects of sodium reduction on overall health.”

Morton Satin, vice-president of science and research for the Salt Institute, added, “It is good to see that this report cautions against drastic sodium reduction efforts to get people to consume dangerously low levels of sodium of 1,500 mg a day. There is no scientific justification for population-wide sodium reduction to such low levels and the recognition by the I.O.M. experts that such low levels may cause harm may help steer overzealous organizations away from reckless recommendations.”

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