A sophisticated analysis, just published in the journal Hypertension and based on three distinct computer-modeling approaches, found that meaningful reductions in Americans' average intake of dietary sodium could save between 280,000 and 500,000 lives over the next decade.
Those are big, impressive numbers. Not all that long ago, this provocative finding would have been a clear and direct goad to public action, for there was widespread acceptance that sodium excess was harmful. While that view still persists among the majority of experts, a vocal minority has voiced enough dissent over recent years to create at least the impression of abiding doubt. There is the possibility, therefore, that the opportunity highlighted in this new study may prove only to be new fodder for interminable and contentious debate. I would like to help preempt that.
The new study ran its several models based separately on observational epidemiology, epidemiologic studies, and intervention trials. We have long had evidence that excessive dietary sodium is harmful, based on just such sources.
Decades of observational epidemiology indicate lower rates of hypertension, stroke, and cardiovascular disease in populations with less salt intake. Of course such studies, such as Intersalt, cannot fully isolate the effects of sodium. Intervention trials, however, such as DASH and related studies can and have--reaching similar conclusions. Transcultural studies that track what happens to health outcomes as groups with the same genes move into different cultural contexts have lent further support.
[See DASH Diet]
On the basis of such aggregated evidence, the Center for Science in the Public Interest has long contended that excess sodium kills 150,000 Americans prematurely each year. While the new analysis suggests that estimate may itself be slightly excessive, it corroborates the fundamental concern.
Of course, the issue has always been that excessive sodium was harmful, and even then, only for those vulnerable to its effects. Sodium, per se, is not only not harmful--it's essential for life. If we don't consume sufficient sodium, we develop hyponatremia (low blood sodium), and if that advances, we die. Most of us who have gone through medical training have seen cases of life-threatening hyponatremia, and it isn't pretty.
The mere possibility of an excessive intake of sodium is a modern anomaly. Marine animals--and long enough ago, that was all animal life--are surrounded by brine, and immune to being pickled by it. In the seas, we had limitless access to sodium, and were at no risk of getting too much.
Our need for sodium became acute only when we hauled ourselves out of that brine, and became terrestrial creatures. On land, sodium is rather hard to come by in adequate supply, let alone excess. Deer will come to a salt lick for that very reason.
But "salty" is one of the several basic flavor categories of food, and like others on that list--notably sweet and savory--tends to stimulate appetite. So while the addition of salt to food originated with efforts at preservation and the prevention of spoilage, more and more has been added over time to make food ever more palatable. Copious additions of salt to processed food count among the reasons why nobody can no longer eat just one.
Of course, there really shouldn't be any debate about the harms of "excess" sodium, because harm is implied by the term "excess." If our sodium intake was not harmful, what basis would there be to define it as excessive? Compared with what?
What the weight of evidence shows is that prevailing intake is, indeed, excessive relative to what is optimal for health. Ambient intake in the United States is excessive in comparison to standards around the world--standards associated with far lower rates of sodium-related chronic diseases, such as hypertension, osteoporosis, stroke, and heart disease. Prevailing levels are excessive compared to our native intake level in a world of pronounceable and recognizable foods, devoid of Golden Arches. Our Stone Age ancestors consumed much more potassium than sodium, and we have reversed that ratio in dramatic fashion.
The fact that too much is harmful doesn't make too little harmless. Deficiency, like excess, is a contingent term: deficient, compared with what? We need a certain sodium level to maintain normal levels in our blood, maintain normal blood pressure, and maintain normal hormonal balance. Neither too much nor too little is good. So studies showing potential harm from very low sodium intake are not surprising.
Nor do such studies invite neglect of the prevailing excess. We would be foolish to neglect global warming (more than we already do) for fear that our remedial efforts could overshoot and induce an ice age. The fixable problem we have should be prioritized over the hypothetical problem we might create if we overshoot absurdly. Let's not overshoot--but let's do something.
What something? Experts argue a need for change in processed foods, which provide 80 percent of the sodium we all ingest. The salt shaker adds only minimally to the problem. As for taking matters into your own hands, you can do so by eating more foods direct from nature. They tend to represent the relative paucity of sodium and abundance of potassium familiar to our ancestors and help shift our own balance of these nutrients toward the native normal.
Those concerned that we have distorted the harmful effects of any given nutrient deserve to be heard. But they go too far when any given study is used to replace the hard-earned aggregation of evidence that preceded it. Scientific evidence is most useful in context. When scientific opinion is batted around like a ping-pong ball, the public health tends to take a beating.
There is no question that dietary patterns at odds with the fundamentals of what we know about the basic care and feeding of Homo sapiens are a major cause of the most egregious injuries imposed on modern public health. There are many minor deficiencies and major excesses contributing to the adversities of our dietary intake, and an excess of sodium is by no means solely responsible for what ails us. But the weight of evidence decisively implicates it as one among the many responsible exposures.
There are, in other words, serious wounds in public health--and there is, along with the rest of a dubious recipe, salt in those wounds.
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David L. Katz, MD, MPH, FACPM, FACP, is a specialist in internal medicine and preventive medicine, with particular expertise in nutrition, weight management, and chronic-disease prevention. He is the founding director of Yale University's Prevention Research Center, and principal inventor of the NuVal nutrition guidance system. Katz was named editor-in-chief of Childhood Obesity in 2011, and is president-elect of the American College of Lifestyle Medicine.