Salt in our diet: The impact of recent studies

We have long had abundant reason to believe that most of us living in the modern world consume too much sodium and would benefit from consuming less. But whether the topic is salt, or saturated fat, or calories, or even the health effects of consuming vegetables and fruits — saltation (the jumping from one position to another) seems to be the prevailing inclination in modern nutrition. Certainly it is the inclination that predominates in the popular press. Salt is just the latest nutrient to get caught up in that proclivity.

This isn’t the first time salt claimed its 15 minutes of notoriety. Just less than a year ago, I was prompted to address this issue by an IOM report questioning the gospel of “less is better” with regard to sodium intake. Two recent studies compel me to revisit the topic now. For those who like the punch line up front, I can tell you my conclusion is much as it was. I remain convinced that most of us consume too much salt, and would benefit from reducing our intake. And yes, of course, it’s possible to consume too little.

Of the two recent studies on salt intake and health outcomes, predictably the one that challenged the prevailing view garnered more media attentionThat study, published in the American Journal of Hypertension in early April, was a meta-analysis examining sodium intake in populations around the world and its association with both all-cause mortality and cardiovascular disease.

The authors concluded that mortality and heart disease rates were higher among those with both low and high sodium intake, and lower for those with intake in the middle range. Because dietary guidelines from the relevant authorities, including the IOM, the CDC, and the USDA all emphasize a reduction in our customarily excessive salt intake, the more provocative message in this study was the potential danger in consuming too little. So “salt guidelines are too low” was the common pop culture assessment.

But there are a few problems with that conclusion. First, as the study authors stated, the increased risks of both heart disease and mortality were greater with high sodium intake, than with low. So if we were ranking our concerns based on this study alone, excess sodium would still be the bigger problem.

Second, the authors noted their meta-analysis was based almost entirely on observational, not intervention, trials. This meant studies simply looked at variation in sodium intake and compared that to variation in health outcomes. Studies like that beg the question: What accounted for the sodium variation in the first place? Some health conscious people may have a very low intake of sodium, but others likely to land there are people with maladies affecting the heart or kidneys, people who are under-nourished for any reason, and so on. The authors attempted to account for such considerations, but acknowledged a limited ability to do so. In other words, this study had limited capacity to tell us whether low sodium intake resulted in poor health, or whether poor health resulted in low sodium intake. Chances are there was some of both in the mix.

The more recent study, published online in the British Medical Journaltook headlines in the opposite direction: Too much sodium is the problem after all. For this study, investigators tracked dietary patterns, including sodium intake, and sodium excretion, in representative samples of the population of England. Over the past decade, they tracked a number of dietary changes, and conducted analyses to determine the association of each with health outcomes. The particularly noteworthy findings were a reduction in sodium intake and excretion, associated with a population-wide reduction in mean blood pressure, in turn associated with a marked reduction in the mortality rate from both stroke and heart disease.

This study is subject to limitations of its own. But it does not suffer the problem of temporal association that bedevils the first. The gist is clear: A population-wide reduction in sodium intake over the past decade is almost certainly at least part of the reason for a population-wide reduction in blood pressure, and cardiovascular mortality.

But conclusions about sodium in our diets should not be based on any one study, whatever its strengths or weaknesses, but rather the overall weight of evidence. That remains rather clear. Average sodium intake levels in the U.S. and much of the modernized world are higher than advised. Intervention studies, such as DASH, that have lowered levels to approximate prevailing guidelines, have lowered blood pressure as a result. Blood pressure reduction in turn has been strongly and consistently associated with reduced risk of both heart disease and stroke.

But there is more. Paleo diet enthusiasts rightly note that our native dietary intake pattern is likely to be “good” for us, since it is the pattern to which we are adapted. That adaptation is a powerful influence – it’s why koala bears should eat eucalyptus leaves, and lions should eat wildebeest. It stands to reason that adaptation is relevant to our species as well. There are many implications of “native” eating for Homo sapiens, but one of them is a much higher intake of potassium than sodium. The modern diet typically reverses this ratio. Arguments for sodium reduction thus derive from both modern science, and paleoanthropology.

Finally, the source of sodium is a relevant consideration. Roughly 80 percent of the sodium in the typical American diet comes not from personal use of a salt shaker, but from salt processed into our food before ever we get our hands on it. This implies that sodium intake tends to come down with consumption of less processed foods overall. While reduced sodium intake is likely beneficial in such context, the context of a less processed diet is apt to be beneficial in a variety of ways. With sodium, as with other nutrients of concern, if we get the foods and dietary pattern right, nutrients tend to take care of themselves.

Of course, the contention that we should reduce ambient sodium intake not by focusing on sodium, but by eating “food, not too much, mostly plants,” invites the customary rebuttals: That’s elitist, unrealistic, too expensive, and too hard. I disagree with these assertions and have addressed them in very practical terms. My group has studied the costs of trading up to better, less-processed, and among other things, less-salty options in any given food category, and found that it can generally be done without spending more money. We have developed and studied a nutrition guidance system and a free food label literacy program, showing that both can help people get there from here. Of importance to everyone who isn’t a card-carrying member of the foodie elite, it is possible to trade up nutrition (and dial down sodium) without swapping out chips for chard; it’s possible to make meaningful progress by eating better chips.

Sodium is an essential nutrient; of course we could, in principle, eat too little. We could, as well, drink too much water. Or exercise too much. Or sleep excessively. Or spend too much time fortifying bonds of friendship. I suppose we might devote too much of each day to hugging.

But really, what are the odds? We sleep and hug too little, work and stress too much. The theoretical dangers of overshooting are not a good reason to neglect what is currently broken.

Average sodium intake in the U.S. hovers well about 3,000 mg per day. While there is legitimate debate about health effects at levels below 2,300 mg per day, there is little about levels between here and there. Just to hit the targets in which we do have confidence, we have a long way to go. So it seems very premature to start encouraging people to worry about overshooting.

The prevailing fashion in nutrition, if not all of health news, is contrarianism. Cutting back on salt was yesterday’s news. If today’s news were the same as yesterday’s news, we might not be confused, and desperately in need of tomorrow’s news to help sort it all out. We can’t have that! So as never before, contrarians and iconoclasts own the headlines.

But they don’t really own the science, which is, as ever, a product of the gradual accumulation of data and genuine understanding over time – not the single study that grabs 15 minutes in the spotlight. And they don’t own our common sense — which should tell us that worrying about doing too much is not a good reason to avoid doing enough.

The saltatory headlines notwithstanding, an excess of sodium is the salient, clear, and present danger for modern societies. While allowing for the hypothetical hazards of going too far, we should focus for now on fixing what we know to be broken.

David L. Katz is the founding director, Yale-Griffin Prevention Research Center. He is the author of Disease-Proof: The Remarkable Truth About What Makes Us Well.

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