A Little Less Salt Results in Big Gains in Health Benefits and Years of Life

Lynda A. Szczech, MD


August 05, 2010

Population Strategies to Decrease Sodium Intake and the Burden of Cardiovascular Disease: A Cost-Effectiveness Analysis

Smith-Spangler CM, Juusola JL, Enns EA, Owens DK, Garber AM
Ann Intern Med. 2010;152:481-487, W170-173


Considerable focus has been given to sodium intake and its association with the improvement in public health in response to the United Kingdom’s recent success in lowering population sodium intake. Smith-Spangler and colleagues used simulated models to understand how a reduction in population sodium intake would save healthcare costs to society, as mediated by a reduction in blood pressure and subsequent decrease in the rate of myocardial infarction (MI) and stroke.

Study Summary

Using computer simulation, the authors took a defined hypothetical population and aged its members to examine the effects of sodium intake on long-term outcomes. During this electronic aging process, some members of the simulated population developed cardiovascular events (in this case, MI and stroke). Some of these events were fatal, and some were not. Patients who developed nonfatal events continued to age within the cohort and incurred higher risk for additional events and death than those who did not experience cardiovascular events. With each simulated year that passed, the population changed in terms of age, degree of comorbidity, and event rate. This iterative process was accomplished using multiple sets of probabilities or assumptions. Key factors inherent in this analysis include the expected reduction in sodium intake that the various strategies proposed will accomplish, the effect of that reduction on blood pressure, and the effect of the reduction in blood pressure on cardiovascular event rates. In addition, life expectancy after a cardiovascular event and the cost of the cardiovascular event play key roles in the conclusions of these analyses.

To develop a range of assumptions and probabilities to test, Smith-Spangler and colleagues used multiple valid and appropriate data sources, including the Medical Panel Expenditure Survey, the Framingham Heart Study, and Dietary Approaches to Stop Hypertension Trial. Given that a key feature in the quality of simulated patient populations is the validity of the underlying probabilities and assumptions, the importance of using valid sources and testing multiple ranges within those estimates needs to be underscored. US census data were used to identify numbers of persons aged 40 to 85 years.

On the basis of these methods and data sources, the study estimated that a reduction of 9.5% in population sodium intake would result in a modest decrease in mean systolic blood pressure of 1.25 mm Hg in persons aged 40 and 85 years. This reduction would, however, result in 513,000 fewer strokes and 480,000 fewer MIs and an increase in more than 1.3 million years of life for US adults who are currently 40 to 85 years of age. The reductions in stroke and MI would result in a savings of $32.1 billion in direct medical costs. These estimates were derived from the assumption that a collaboration between government and industry would result in a voluntary reduction in the sodium content in foods. As an alternative to voluntary reduction in sodium content, the authors also examined the decrease in sodium intake that would be achieved by levying a sodium tax, and they concluded that a sodium tax would provide similar although slightly lower reductions in events and monetary savings. The calculated effects on health achieved by a sodium tax amounted to approximately 327,000 strokes and 306,000 MIs averted, as well as a gain of 840,000 years of life and a savings of $22.4 billion dollars in direct medical costs.

The authors were sensitive to the effect of reduction in dietary salt intake on quality of life. Although they acknowledged that the effect would probably be minimal, they performed analyses to estimate what reduction in quality of life would substantially affect the benefits to clinical outcomes demonstrated in the simulations.


Given that the strength or limitations of a simulation such as this can largely be gauged through the validity of the assumptions, one important point should be noted: The cost savings presented here are striking. If the causal pathway of decreased sodium leading to decreased blood pressure and decreased cardiovascular events is valid on a population level, then one key limitation of this analysis should also be considered. Blood pressure influences many comorbid conditions, such as congestive heart failure and chronic kidney disease. These comorbidities, as well as others, affect both lifespan and healthcare costs. The failure to include such events in this analysis undoubtedly resulted in an underestimate of the cost savings that would be achieved by a sodium reduction initiative, if one were implemented.

In addition to the staggering public health benefit and cost savings that would be achieved by lowering the population’s sodium intake, this analysis makes conjecture on the relative successes of 2 different strategies to implement such an initiative. For various reasons, the authors conclude that voluntary reduction by the food industry in the sodium levels of prepared foods would result in an increased overall benefit and a lesser likelihood of discrimination against poor persons than would be achieved by the levying of a salt tax. The implementation of either strategy would take coordination of industry and government and is likely to evolve gradually. In the interim, our role as clinicians is to continue to educate the public on dietary choices and the role that decreased sodium intake can play in their long-term health. In the absence of large-scale cooperation by the food industry, this education process will need to be accomplished, physician by physician, person by person, and certainly crystal by crystal.



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