The Sodium Debate

I know that the news today can be overwhelming, even just mentioning the word facts can trigger all sorts of reactions.  I’m Dr. Michael Greger and I happen to really like facts!  So, I’ve devoted my life to learning all there is to know about the latest nutrition research, so that you and your family can lead healthier, more productive lives.

On today’s show we tackle a salty topic, sodium!  In our first story we ask – Is the sodium debate a legitimate scientific disagreement or a “controversy” manufactured by industry?

For decades, a sometimes furious battle has raged amongst scientists over which the extent to which elevated salt consumption contributes to death, with one camp calling it a public health hazard that requires vigorous attack and another claiming the risks of dietary salt excess are exaggerated, even to the point of calling salt reduction probably, “the largest delusion in the history of preventive medicine”. The other side calls this denialism ethically irresponsible, especially when millions of lives are at stake every year. 

Described two sides of the debate may be falling into the trap of false equivalency though, as the superhero sounding “World Hypertension League” points out, there is strong scientific consensus that reducing salt saves lives and, like the climate change debate, most authorities are on one side with only the industry affected and their paid consultants and a few dissenting scientists on the other.  Nearly all government-appointed bodies and nutrition experts who have considered the evidence have recommended we collectively cut our salt intake about in half, described as extreme though by those defending the industry.  After all, just a small fraction of Americans actually get their sodium intake that low.  Therefore, the salt skeptics say, the human experience for very low levels of sodium consumption is extremely sparse.  Extremely sparse?  The reality is the exact opposite!  The human experience is living for millions upon millions of years without Cheetos or a salt shaker in sight.  We evolved to be salt-conserving machines and when we’re plunked down into snack food and KFC country, we develop high blood pressure. 

But, in the few populations left that don’t eat salt that continue to eat as much as we have for millions of years, our leading killer risk factor—hypertension—is practically nonexistent. 

When we take people out-of-control hypertension and bring them back down to the sodium levels we were designed to eat, the ravages of the disease can even be reversed. 

So, why is there still a debate?  If salt hidden in foods kills millions of people around the world, why are efforts to cut dietary salt being met with fierce resistance?  Well, salt is big business for the processed food and meat industry and, so, according to the head of the World Health Organization’s Collaborating Center on Nutrition, we get the familiar story.  Just like the tobacco industry spent decades trying to manufacture doubt and confuse the public, the salt industry does the same, but the controversy is fake. 

The evidence for salt reduction is clear and consistent.  Most of the “contradictory research” comes from scientists linked to the salt industry.  However, it takes skill to spot the subterfuge, because the industry is smart enough to stay behind the scenes—covertly paying for studies designed to downplay the risks.  All they have to do is manufacture just enough doubt to keep the controversy alive.  The likes of the World Hypertension League have been described as a near popgun against the weapons-grade fire power of salt-encrusted industries, who look disdainfully at the do-gooder health associations who erect road blocks on the path to profits. Lest we forget, notes this editorial in the Journal of the Canadian Medical Association, high blood pressure is big business for the drug industry too whose blood pressure billions might be threatened should we cut back on salt.  If we went sodium-free and eliminated the scourge of hypertension, not only would Big Pharma suffer, what about doctors? The #1 diagnosis adults see doctors with is high blood pressure, nearly 40 million doctor visits a year, and so maybe even the BMW industry might be benefiting from keeping the salt debate alive.

What about the studies that show a so-called “u-shaped curve,” where yeah too much sodium is bad, but too little may be bad too? Here’s what they found out.

High blood pressure is not the only harmful effect of too much salt—it’s also been tied to stomach cancer, kidney stones, bone loss, obesity even, direct damage to our kidneys, arteries, and heart. But, as I reviewed before, there is a consensus that dietary sodium plays a significant role in raising people’s blood pressure, a dispute that has now finally been resolved.

So, there’s this unequivocal evidence that increased sodium intake is associated with increased blood pressure, and we know that increased blood pressure leads to increased risk of vascular diseases like strokes, aneurisms, and atherosclerosis.  So, to quote the long time editor-in-chief of the American Journal of Cardiology, “We all must decrease our salt intake!”, as other authorities have echoed.

So, how is the food industry going to keep the salt controversy alive? If salt leads to high blood pressure and high blood pressure leads to disease—if A leads to B, and B leads to C, then A should lead to C—the logic seems sound. Blood pressure is one of the best validated surrogate markers for cardiovascular disease, and when countries have tried cutting down on salt, it seems to have worked.

Campaigns in England were able to successfully bring down salt consumption. Blood pressures dropped, and so did rates of heart disease and stroke. Now, they were also successfully able to bring down cholesterol levels and smoking, and improve fruit and vegetable consumption, but in Japan they dropped salt intake while eating a worse diet and smoking more, and still saw a large reduction in stroke mortality.

Based on what they were able to achieve in Finland, one daily teaspoon of salt may mean between 25 and 50% more deaths from heart attacks and strokes. But are there randomized controlled trials to show that? They’ve never randomized people into two groups, one low-sodium, one not, followed them out for 20 years to see if the differences in blood pressures translated into the expected consequences. But for that matter, such a study has never been done on smoking either. Imagine randomizing a group of smokers to quit smoking or stay smoking for ten years to see who gets lung cancer.

First of all, it’s hard to get people to quit, just like it’s hard to keep people on a low-salt diet, and would it be ethical to force people to smoke for a decade knowing from the totality of evidence that it’s likely to hurt them? That’s like the Tuskegee experiment. We can’t let the perfect be the enemy of the good; we’re never going to get a decade-long randomized trial, but in 2007 we got this: There have been randomized trials of sodium reduction, but they haven’t lasted long enough to provide enough data on clinical outcomes. For example, the famous TOHP trials, which randomized thousands into at least 18 months of salt reduction. What if you followed up with them 10 to 15 years after the study was over, figuring maybe some in the low-salt group stuck with it and, indeed, cut sodium intake by 25 to 35%, and we may end up with 25% lower risk of heart attacks, and strokes, and other cardiovascular events.

This was considered the final nail in the coffin for salt, addressing the one remaining objection to universal salt reduction, the first study to show not only a reduction in blood pressure, but a reduction in hard end points—morbidity and mortality—by reducing dietary sodium intake. Case closed, 2007.

But when billions of dollars are at stake, the case is never closed. One can just follow the press releases of the Salt Institute. For example, what about the Institute of Medicine report saying salt reduction may cause harm in certain patients with decompensated congestive heart failure? An analysis of those studies has since been retracted out of concern that the data may have been falsified. But it’s certainly possible that those with serious heart failure, already severely salt depleted by high dose salt-wasting drugs, may not benefit from further sodium restriction. But for the great majority of the population, the message remains unchanged.

What about the new study published in the American Journal of Hypertension?  They found that the amount of salt we are eating is just fine, suggesting a kind of u-shaped curve where too much sodium is bad, but too little could be bad too.

But, those biased less towards Big Salt and more towards Big Heart have noted that these studies have been widely misinterpreted, stirring unnecessary controversy and confusion. It basically comes down to three issues: measurement error, confounding, and reverse causality. All these data came from studies that were not designed to assess this relationship, and so, tended to use invalid sodium estimates, just because it’s so hard to do multiple 24-hour urine collections necessary to get a good measurement.

And, in the U.S., many of those eating less salt are simply eating less food, maybe because they’re so sick. So, no wonder they’d have higher mortality rates. So, compiling these studies together is viewed as kind of garbage in garbage out. But why would they do that?  They claim to have no conflicts of interest. But when confronted with evidence showing at least one of the co-authors received thousands of dollars from the Salt Institute, they replied that well, “they didn’t get more than $5,000 from them in the last 12 months,” so, that’s how they could get out of saying they had a conflict of interest. 

If you, instead, only look at the trials in which they did the gold-standard 24-hour collections in healthy people to avoid the reverse causation and controlled for confounders, the curve instead looks like this: a continuous decrease of cardiovascular disease events, like heart attacks and strokes, as sodium levels get lower and lower, a 17% increase in risk of cardiovascular disease for every gram of sodium a day. And, this is for people without high blood pressure, for which we’d expect the benefit to be even greater.

Unfortunately, the media widely misreported the findings and a false sense of controversy has been broadcast, confusing the public. But it’s not just the media. When editorials are published on the subject in some of the most prestigious medical journals in the world, you don’t expect them to be written by those who got paid personal fees by Big Salt.  And before accepting money from the Salt Institute, she was accepting money from the Tobacco Institute, and was a frequent expert witness in defense of Philip Morris and other tobacco companies. So, if that’s who the New England Journal of Medicine chooses to editorialize about salt, you can see the extent of industry influence. The editor-in-chief of the American Journal of Hypertension himself worked for many years as a consultant to the Salt Institute.  Rather than reformulate their products with less sodium and save lives, food manufacturers have lobbied governments, refused to cooperate, encouraged misinformation campaigns, and tried to discredit the evidence.

Like any group with vested interests, the food industry resists regulation. Faced with a growing scientific consensus that salt increases blood pressure, major food manufacturers have adopted desperate measures to try to stop governments from recommending salt reduction. After all, salt is the main source of flavor in processed foods. Of course, they could improve the flavor by adding real ingredients, but like making a Pop-Tart with actual strawberries, would be more expensive, cut into profits.

The evidence that they’re trying to discredit includes double-blind randomized trials dating back decades. You take people with high blood pressure, put them on a sodium-restricted diet, and their blood pressure drops. Then, if you keep them on a low-salt diet and add a placebo, nothing happens. But if you, instead, give them salt in the form of a time-release sodium pill secretly, their blood pressure goes back up. And, the more sodium you secretly slip them, the higher their blood pressure climbs.

Even just a single meal can do it. If you take people with normal blood pressure and give them a bowl of soup containing the amount of salt a regular meal might contain and their blood pressure goes up over the next three hours compared to the same soup with no added salt. Why though? High blood pressure appears to be our body’s way to push excess salt out of our system. 

Dozens of such studies have been done, showing that if we reduce our salt intake, we can reduce our blood pressure, and the greater the reduction, the greater the benefit. The so-called DASH diet, which I’ve covered before, commonly used to capture the blood pressure benefits of a more plant-based diet.  But, how do we know the benefits have anything to do with eating less salt instead of just eating more fruits and vegetables? Because it was put to the test.

Sure, eating healthier lowers blood pressure no matter how much salt we eat, but even if we stick to the same diet, lowering salt helps independently of other dietary improvements.

You can do this on a community level. You take two matched villages that both start out about the same. In the control village, on average, blood pressures went up and/or stayed the same. But in the village where they were able to cut down on salt intake, blood pressures went down, whereas if we don’t cut down, chronic high salt intake can lead to a gradual increase in blood pressure throughout life, as shown in the famous Intersalt Study. Fifty-two centers from 32 countries participated with hundreds of participants each, and four of those centers were in populations that ate so little salt they actually complied with the American Heart Association guidelines for salt reduction–something less than 1% of Americans achieve.

In a population where everyone makes the cutoff, not a single case of high blood pressure was found—not one case of high blood pressure, but not only that, the older folks had the same blood pressure as the teenagers.

This is why including such populations is so important. If you just look at the 48 centers in the industrialized Western world, there does not appear to be any relationship between rising blood pressure with age and how much sodium people are getting every day. Now, the salt industry looks at this and says “Aha!—see I told you so, no relationship between salt and increasing blood pressures as you get older.” But maybe that’s because they’re all getting too much salt. If you add in those low-salt populations that get little or no high blood pressure as they get older, you end up with a highly statistically significant relationship between increasing sodium and increasing blood pressure, but only if you include people that actually comply with the salt guidelines. As with so many lifestyle interventions, they only work if you actually do it.

To see any graphs, charts, graphics, images or studies mentioned here, please go to the Nutrition Facts podcast landing page. There, you’ll find all the detailed information you need – plus links to all the sources we cite for each of these topics.

Be sure to check out my How Not to Die Cookbook, beautifully designed, with more than 100 recipes for delicious and nutritious meals, snacks and beverages. All proceeds I receive from the sale of my books go to charity.

NutritionFacts.org is a nonprofit, science-based public service, where you can sign up for free daily updates on the latest in nutrition research via bite-sized videos and articles.

Everything on the website is free. There’s no ads, no corporate sponsorship.  It’s strictly non-commercial.  I’m not selling anything. I just put it up there as a public service, as a labor of love—as a tribute to my grandmother – whose own life was saved with evidence-based nutrition.

Thanks for listening to Nutrition Facts.  I’m Dr. Michael Greger.

This is just an approximation of the audio content, contributed by Allyson Burnett.

Please consider volunteering to help out on the site.