New report highlights the dangers of having too little salt in our diet

Shaun Weston15 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.

However, evidence from these studies does not support reduction in sodium intake to below 2,300mg per day, according to 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 3,400mg or more of sodium a day, which is equivalent to about 1½ teaspoons of salt.

The current Dietary Guidelines for Americans urge most people ages 14-50 to limit their sodium intake to 2,300mg 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% of the US population) are advised to follow an even stricter limit of 1,500mg 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 such as 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 2,300mg/day either increases or decreases the risk of heart disease, stroke or all-cause mortality in the general US 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 (ie 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 2,300mg daily) among those with diabetes, kidney disease or heart disease, the evidence on both the benefit and harm isn't strong enough to indicate that these subgroups should be treated differently from the general US population. Thus, the evidence on direct health outcomes doesn't support recommendations to lower sodium intake within these subgroups to or even below 1,500mg daily, and further research is needed to shed more light on associations between lower levels of sodium (in the 1,500 to 2,300mg/day range) and health outcomes, both in the general population and the subgroups.

The report doesn't establish a 'healthy' intake range, because the committee wasn't 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.

Source: Institute of Medicine