The IOM report affirms that the available evidence on associations between sodium intake and direct health outcomes is consistent with population-based efforts to lower excessive sodium intakes. It is likely a result of the limited scope of its investigation that led to the conclusion that “studies on health outcomes are inconsistent in quality and insufficient in quantity to conclude that lowering sodium less than 2,300mg either increases or decreases risk of heart disease, stroke, or all-cause mortality in the general population.”
The IOM committee reviewed only those studies that relate sodium intake to health outcomes. It was not a comprehensive review of the health effects of sodium.
In particular, it did not include evidence on how sodium reduction lowers blood pressure, a key determinant of health and the largest determinant of preventable mortality worldwide, when formulating its recommendations.
The IOM report does not recommend against 1,500mg, rather, it states that there aren’t enough data on sodium intake and direct health outcomes to recommend lowering to that level, and that the current data are inconsistent.
Sodium is no different from many other nutrients and foods in that “hard outcome” data from randomized trials are not available and likely will not be available, because of the difficulty of conducting such a trial. Therefore, researchers look to the well-established body of evidence of sodium’s effect on blood pressure, because blood pressure is widely recognized as a suitable proxy indicator for risk of heart disease and stroke.
In fact, the 2010 IOM report, “Evaluation of Biomarkers and Surrogate Endpoints in Chronic Disease,” recommended that blood pressure be used as a proxy for coronary heart disease.
The earlier IOM report also indicated that blood pressure is a suitable proxy for cardiovascular disease mortality and morbidity. This is the rationale for the AHA’s recommendation that all Americans consume less than 1,500 mg sodium per day.
For example, the landmark National Heart, Lung, and Blood Institute’s Dietary Approaches to Stop Hypertension (DASH) study initially found that eating a diet rich in fruits, vegetables and low-fat dairy foods and with reduced saturated and total fat could substantially lower blood pressure. Subsequently, when the DASH-Sodium Study combined the DASH diet with reductions in sodium to 1500 mg per day, average blood pressure was reduced by 8.9/4.5 mm Hg compared to a control diet.
Finally, a majority of the American population either has high blood pressure or is at risk for developing it because they are African American, over the age of 51, or have diabetes or chronic kidney disease. There is strong scientific evidence that these groups are especially sensitive to the blood pressure lowering effects of sodium reduction going from 2,300 to 1,500 mg per day.
Reducing sodium also could rein in health costs. One estimate suggests a national effort that reduces population sodium intake by 1,200 mg per day could reduce the health burdens related to heart disease in addition to reducing costs by up to $24 billion per year.
The AHA urges an intensive focus on sodium reduction as a critical component of public health efforts to promote cardiovascular health and prevent cardiovascular disease. Successful sodium reduction requires action and partnership at all levels—individuals, healthcare providers, professional organizations, public health agencies, governments and industry.
Dr. Antman is a spokesperson for the AHA and is a cardiologist at Brigham and Women’s Hospital in Boston.