IOM: Studies Do Not Support Reduction in Sodium Intake to Below 2,300mg Per Day

16 May 2013 --- Recent studies that examine links between sodium consumption and health outcomes support recommendations to lower sodium intake from the very high levels some Americans consume now, but evidence from these studies does not support reduction in sodium intake to below 2,300 mg per day, says a new report from the Institute of Medicine.

Despite efforts over the past several decades to reduce dietary intake of sodium, a main component of table salt, the average American adult still consumes 3,400 mg or more of sodium a day – equivalent to about 1 ½ teaspoons of salt. The current Dietary Guidelines for Americans urge most people ages 14 to 50 to limit their sodium intake to 2,300 mg daily. People ages 51 or older, African Americans, and people with hypertension, diabetes, or chronic kidney disease – groups that together make up more than 50 percent of the U.S. population – are advised to follow an even stricter limit of 1,500 mg per day. These recommendations are based largely on a body of research that links higher sodium intakes to certain “surrogate markers” such as high blood pressure, an established risk factor for heart disease.

The expert committee that wrote the new report reviewed recent studies that in contrast examined how sodium consumption affects direct health outcomes like heart disease and death. “These new studies support previous findings that reducing sodium from very high intake levels to moderate levels improves health,” said committee chair Brian Strom, George S. Pepper Professor of Public Health and Preventive Medicine at the University of Pennsylvania Perelman School of Medicine. “But they also suggest that lowering sodium intake too much may actually increase a person’s risk of some health problems.”

While cautioning that the quantity of evidence was less-than-optimal and that the studies were qualitatively limited by the methods used to measure sodium intake, the small number of patients with health outcomes of interest in some of the studies, and other methodological constraints, the committee concluded that:

• evidence supports a positive relationship between higher levels of sodium intake and risk of heart disease, which is consistent with previous research based on sodium’s effects on blood pressure;
 
• studies on health outcomes are inconsistent in quality and insufficient in quantity to conclude that lowering sodium intake levels below 2,300 mg/day either increases or decreases the risk of heart disease, stroke, or all-cause mortality in the general U.S. population;
 
• evidence indicates that low sodium intake may lead to risk of adverse health effects among those with mid- to late-stage heart failure who are receiving aggressive treatment for their disease;

• there is limited evidence addressing the association between low sodium intake and health outcomes in population subgroups (i.e., those with diabetes, kidney disease, heart disease, hypertension or borderline hypertension; those 51 years of age and older; and African Americans). While studies on health outcomes provide some evidence for adverse health effects of low sodium intake (in ranges approximating 1,500 to 2,300 mg daily) among those with diabetes, kidney disease, or heart disease, the evidence on both the benefit and harm is not strong enough to indicate that these subgroups should be treated differently from the general U.S. population. Thus, the evidence on direct health outcomes does not support recommendations to lower sodium intake within these subgroups to or even below 1,500 mg daily; and

• further research is needed to shed more light on associations between lower levels of sodium (in the 1,500 to 2,300 mg/day range) and health outcomes, both in the general population and the subgroups.

The report does not establish a “healthy” intake range, both because the committee was not tasked with doing so and because variability in the methodologies used among the studies would have precluded it.

The recent studies suggest that dietary sodium intake may affect heart disease risk through pathways in addition to blood pressure. “These studies make clear that looking at sodium’s effects on blood pressure is not enough to determine dietary sodium’s ultimate impact on health,” said Strom. “Changes in diet are more complex than simply changing a single mineral. More research is needed to understand these pathways.”

The report was sponsored by the Centers for Disease Control and Prevention. Established in 1970 under the charter of the National Academy of Sciences, the Institute of Medicine provides independent, objective, evidence-based advice to policymakers, health professionals, the private sector, and the public. The National Academy of Sciences, National Academy of Engineering, Institute of Medicine, and National Research Council make up the National Academies. A committee roster follows.

CSPI Nutrition Director Bonnie Liebman responded to the report by stating: “The new sodium report from the Institute of Medicine should not keep the government, food industry, health professionals, and consumers from acting on a public health problem of critical importance. As the IOM itself stated in 2010, urgent government action, including mandatory limits on salt in packaged foods, is required to help Americans bring their sodium consumption down to safe levels.”

“The committee found too little evidence to say whether the safest intake—the green zone—is below 2,300 milligrams a day or below 1,500 milligrams a day. What the committee failed to emphasize is that most Americans are deep in the red zone, consuming 3,500 to 4,000 milligrams of sodium a day. It's clear that those excessive levels increase the risk of high blood pressure, heart attacks, and strokes. Whether we aim for 2,300 or 1,500 milligrams a day is irrelevant until we move down out of the red zone.”

“At restaurants, you can get roughly 2,000 milligrams of sodium from just one burrito, a single-serve pizza, or an order of kung pao chicken, and at least 1,000 milligrams from a typical sandwich or burger. As the IOM concluded in 2010—and as our new study published yesterday in JAMA Internal Medicine confirms—getting down to 2,300 will be nearly impossible until the government phases in reasonable limits on the sodium content of foods.”

“The committee was boxed in by a narrow charge to examine only studies that looked at hard endpoints like heart attacks and strokes. Because of flaws in those studies, the committee did not conclude that low sodium intakes are harmful.”

“No large scale studies have tested whether sodium intakes below 1,500 milligrams a day reduce the risk of heart attacks and strokes. Instead, health authorities have rightly relied on a mountain of evidence that higher sodium intakes raise blood pressure, and that high blood pressure raises the risk of cardiovascular disease.”

Dr. Leon Bruner, Chief Science and Regulatory Affairs Officer for the Grocery Manufacturers Association (GMA), responded to the new IOM report by stating: “We welcome the release of today’s IOM report on “Sodium Intake in Populations: Assessment of Evidence” and commend the Committee members for their continued thoughtful and deliberative work on this important public health issue. We are very pleased by the committee’s finding that there is insufficient scientific evidence to support a lowering of daily sodium intake levels to 1,500 milligrams. We also note with interest the Committee’s acknowledgement of the new research pointing to possible adverse health effects in some populations from consuming too little sodium.
 
“Food and beverage manufacturers are committed to providing consumers with the product choices they need to achieve reduced sodium intake levels. Our industry has developed thousands of products with reduced, low or no sodium and has also silently and incrementally reformulated many products to reduce the amount of sodium within consumer taste preferences.
 
“Reducing sodium in products without negatively affecting consumer acceptance must be taken into consideration, because a ‘healthy food’ will not promote health if it is not purchased or eaten.
 
“GMA continues to supports the federal government’s recommendation of no more than 2,300 milligrams of sodium daily for the general population.”