From Heartwire
Lisa Nainggolan
January 21, 2010 (San Francisco, California)— New statistical projections suggest that slashing salt in the US diet by 3 g per day would have huge benefits, reducing the annual number of new cases of coronary heart disease, strokes, and MIs and potentially saving up to 90 000 lives a year. [1].
And even a more modest reduction of 1 g of salt per day would still have significant benefits, Dr Kirsten Bibbins-Domingo (University of California, San Francisco) and colleagues estimate in their paper published online January 20, 2010 in the New England Journal of Medicine. They call for urgent action in terms of a populationwide effort to reduce dietary salt in the US.
In an accompanying editorial [2], Drs Lawrence J Appel and Cheryl AM Anderson (Johns Hopkins University, Baltimore, MD) applaud the new research and say it extends the findings of other studies by demonstrating that such reductions in salt intake could be as beneficial as interventions aimed at smoking cessation, weight reduction, or the use of lipid-lowering medication.
The findings, along with other research, should spur efforts to swiftly implement a public-health approach to salt reduction in the US, they say. The US currently "lags behind many countries when it comes to translating this research into policies that achieve meaningful reductions in dietary salt," say Appel and Anderson. "As we deliberate healthcare reform, let us not neglect this inexpensive yet highly effective public-health intervention for the prevention of disease."
But Dr Michael Alderman (Albert Einstein College of Medicine, Bronx, NY), a well-known critic of policies to reduce salt intake at the population level, does not agree. He told heartwire that while this new study "seems to be a competent estimate of what might happen if BP were reduced--without other effects--based upon what we know from the clinical effects of antihypertensive medications, there is nothing new here but the hope that the effect on a single surrogate end point would translate into a remarkable reduction in morbidity and mortality." This, he says, would be "wonderful if true, but is still without adequate scientific foundation."
New Recommendations on Salt Expected Soon in US?
In their editorial, Appel and Anderson say that despite 40 years of consumer education in the US to try to get people to change their behavior and reduce salt intake, the per capita consumption appears to be increasing or is at best unchanged.
Anderson told heartwire in a recent interview that the situation is pressing: "People are not aware of how much salt they consume, and they are struggling to meet the recommendations." Much of this is due to "the ubiquitous nature of sodium in the food supply," she explains, with approximately 75% of dietary salt coming from processed foods.
As a result, there are currently many initiatives ongoing in the US to try to address the amount of salt added to the food supply. Underpinning these was a petition submitted to the FDA some time ago, to try to revoke its current designation of salt as a food additive "generally regarded as safe."
The agency subsequently held a public meeting, and the Institute of Medicine (IoM) was commissioned to issue a report, "Population-based strategies for reducing salt intake," which is due to come out this spring.
Anderson sits on the IoM panel discussing this issue, and while she says she can't reveal the contents of the upcoming report, "You can imagine there will be recommendations that might be quite different from the 40 years' experience that we have had, because excessive [salt] intake has continued to occur."
Findings Underscore the Need for an Urgent Call to Action
In their study, Bibbins-Domingo et al used the Coronary Heart Disease Policy Model to estimate the benefits of potentially achievable populationwide reductions in dietary salt of up to 3 g per day (1200 mg of sodium per day). Such a reduction would reduce the number of new cases of CHD by 60 000 to 120 000 per year, stroke cases by 32 000 to 66 000, and MIs by up to 99 000, as well as cutting all-cause mortality by almost 100 000, they calculate. This intervention could also save up to 392 000 quality-adjusted life-years and up to $24 billion in healthcare costs annually, they predict.
This postulated dietary reduction of 3 g of salt per day is within the range targeted by some developed countries that have already successfully adopted programs to reduce salt intake, they say.
But recognizing that a 3-g/day reduction may be difficult--given that mean salt intake in the US is extremely high and well above the current daily recommended upper limit of 5.8 g a day--even just a 1-g/day cut in salt intake would provide substantial health benefits and warrant implementation, the researchers note. Such a reduction, gradually achieved between 2010 and 2019, would still be more cost effective than using medications to lower BP in all those with hypertension, for example, they say.
"Lowering salt in the US diet would result in small but measurable reductions in blood pressure across the entire US population, thereby reducing rates of CVD among all adults at risk." In addition, salt reduction would be of proportionately greater benefit in certain subgroups, they note, such as African Americans, who have high rates of hypertension and CVD.
"Our findings underscore the need for an urgent call to action that will make it possible to achieve these readily attainable cardiovascular benefits," they conclude.
Modeling Relies on Assumptions; But Is Evidence Compelling or Not?
Appel and Anderson point out that a feature of the modeling by Bibbins-Domingo et al is "a series of linked assumptions--namely that salt reduction lowers blood pressure and that lowering blood pressure reduces the risk of stroke and CHD."
There is direct evidence of a link between salt and cardiovascular disease from some prospective observational studies and a few available trials with clinical outcomes that concern cardiovascular disease, they note.
"The evidence supporting the call to reduce salt intake as a means of preventing cardiovascular disease is compelling," they state. "There is also evidence that salt reduction may reduce the risk of gastric cancer, end-stage kidney disease, left ventricular hypertrophy, congestive heart failure, and osteoporosis," they add.
But Alderman begs to differ: "As I and others have pointed out, reducing dietary sodium has multiple effects." He says that, "disappointingly," both the editorial and paper "fail to note the complexity . . . the scientific issues involved, and the potential for unintended consequences."
The subject of reducing salt intake via societywide strategies will be probed in an upcoming feature on heartwire .
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