What about the studies that show a “u-shaped curve,” where too much sodium is bad, but too little may be bad too?
Sodium Skeptics Try to Shake Up the Salt Debate
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, and 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 to disease—if A to B, and B to C, then A 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 also successfully brought down cholesterol levels and smoking, and improved 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 to 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 and followed them out for 20 years to see if the differences in blood pressure 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 stuck with it, and indeed, cut sodium intake by 25 to 35%, and we may end up with 25% lower risk of heart attacks, 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 with billions of dollars 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 that sodium reduction may cause harm in certain patients with decompensated congestive heart failure? But 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 that found 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?
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 hard to do the multiple 24-hr 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 like garbage in garbage out. But why would they do that—they claim to have no conflicts of interest? 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, no conflict of interest.
If you instead look only 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 (CVD) events like heart attacks and strokes as sodium levels get lower and lower, a 17% increase in risk of CVD 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 has 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.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.
Please consider volunteering to help out on the site.
- K Bibbins-Domingo, G M Chertow, P G Coxson, A Moran, J M Lightwood, M J Pletcher, L Goldman. Projected effect of dietary salt reductions on future cardiovascular disease. N Engl J Med. 2010 Feb 18;362(7):590-9.
- W C Roberts. High salt intake, its origins, its economic impact, and its effect on blood pressure. Am J Cardiol. 2001 Dec 1;88(11):1338-46.
- B Neal, M A Land, M Woodward. An update on the salt wars-genuine controversy, poor science, or vested interest? Curr Hypertens Rep. 2013 Dec;15(6):687-93.
- A Mente, M J O’Donnell, S Yusuf. Extreme sodium reductions for the entire population: zealotry or evidence based? Am J Hypertens. 2013 Oct;26(10):1187-90.
- F J He, G A MacGregor. Salt reduction lowers cardiovascular risk: meta-analysis of outcome trials. Lancet. 2011 Jul 30;378(9789):380-2.
- N M Kaplan. The final nail for sodium reduction. Curr Hypertens Rep. 2007 Nov;9(5):349-50.
- N R Cook, JA Cutler, E OBarzanek, J E Buring, K M Rexrode, S K Kumanyika, L J Appel, P K Whelton. Long term effects of dietary sodium reduction on cardiovascular disease outcomes: observational follow-up of the trials of hypertension prevention (TOHP). BMJ. 2007 Apr 28;334(7599):885-8. Epub 2007 Apr 20.
- F Godlee. The food industry fights for salt. BMJ. 1996 May 18;312(7041):1239-40.
- J J DiNicolantonio, P Di Pasquale, R S Taylor, D G Hackam. Low sodium versus normal sodium diets in systolic heart failure: systematic review and meta-analysis. Heart. 2013 Mar 12.
- M Jun, B Neal. Low dietary sodium in heart failure: a need for scientific rigour. Heart. 2014 Nov;100(21):e2.
- P K Whelton, L J Appel, R L Sacco, C A Anderson, E M Antman, N Campbell, S B Dunbar, E D Frohlich, J E Hall, M Jessup, D R Labarthe, G A MacGregor, F M Sacks, J Stamler, D K Vafiadis, L V Van Horn. Sodium, blood pressure, and cardiovascular disease: further evidence supporting the American Heart Association sodium reduction recommendations. Circulation. 2012 Dec 11;126(24):2880-9.
- F J. He, G A MacGregor. Salt Intake and Mortality. Am J Hypertens. 2014 Nov; 27(11): 1424.
- N Graudal, G Jurgens, B Baslund, M H Alderman. Compared with usual sodium intake, low- and excessive-sodium diets are associated with increased mortality: a meta-analysis. Am J Hypertens. 2014 Sep;27(9):1129-37.
- P K Whelton, L J Appel. Sodium and cardiovascular disease: what the data show. Am J Hypertens. 2014 Sep;27(9):1143-5.
- N Graudal, M H Alderman. Response to “Salt Intake and Mortality”. Am J Hypertens. 2014 Nov; 27(11): 1425.
- F J He, S Pombo-Rodrigues, G A MacGregor. Salt reduction in England from 2003 to 2011: its relationship to blood pressure, stroke and ischaemic heart disease mortality. BMJ Open. 2014 Apr 14;4(4):e004549.
- N R Campbell, F P Cappuccio, S W Tobe. Unnecessary controversy regarding dietary sodium: a lot about a little. Can J Cardiol. 2011 Jul-Aug;27(4):404-6.
- N R Cook, L J Appel, P K Whelton. Lower levels of sodium intake and reduced cardiovascular risk. Circulation. 2014 Mar 4;129(9):981-9.
- S Oparil. Low sodium intake--cardiovascular health benefit or risk? N Engl J Med. 2014 Aug 14;371(7):677-9.
- NA. CMJE Form for Disclosure of Potential Conflicts of Interest
- T C Beard. Comment on Editorial about salt intake. Kidney International (2007) 71, 86. doi:10.1038/sj.ki.5001952.
- J Tuomilehto, P Jousilahti, D Rastenyte, V Moltchanov, A Tanskanen, P Pietinen, A Nissinen. Urinary sodium excretion and cardiovascular mortality in Finland: a prospective study. Lancet. 2001 Mar 17;357(9259):848-51.
- H E de Wardener, G A MacGregor. Harmful effects of dietary salt in addition to hypertension. J Hum Hypertens. 2002 Apr;16(4):213-23.
- N R Campbell, D T Lackland, M L Niebylski. 2014 dietary salt fact sheet of the World Hypertension League, International Society of Hypertension, Pan American Health Organization technical advisory group on cardiovascular disease prevention through dietary salt reduction, the World Health Organization collaborating centre on population salt reduction, and World Action on Salt & Health. J Clin Hypertens (Greenwich). 2015 Jan;17(1):7-9.
Images thanks to JD Hancock via Flickr.
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, and 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 to disease—if A to B, and B to C, then A 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 also successfully brought down cholesterol levels and smoking, and improved 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 to 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 and followed them out for 20 years to see if the differences in blood pressure 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 stuck with it, and indeed, cut sodium intake by 25 to 35%, and we may end up with 25% lower risk of heart attacks, 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 with billions of dollars 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 that sodium reduction may cause harm in certain patients with decompensated congestive heart failure? But 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 that found 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?
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 hard to do the multiple 24-hr 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 like garbage in garbage out. But why would they do that—they claim to have no conflicts of interest? 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, no conflict of interest.
If you instead look only 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 (CVD) events like heart attacks and strokes as sodium levels get lower and lower, a 17% increase in risk of CVD 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 has 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.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.
Please consider volunteering to help out on the site.
- K Bibbins-Domingo, G M Chertow, P G Coxson, A Moran, J M Lightwood, M J Pletcher, L Goldman. Projected effect of dietary salt reductions on future cardiovascular disease. N Engl J Med. 2010 Feb 18;362(7):590-9.
- W C Roberts. High salt intake, its origins, its economic impact, and its effect on blood pressure. Am J Cardiol. 2001 Dec 1;88(11):1338-46.
- B Neal, M A Land, M Woodward. An update on the salt wars-genuine controversy, poor science, or vested interest? Curr Hypertens Rep. 2013 Dec;15(6):687-93.
- A Mente, M J O’Donnell, S Yusuf. Extreme sodium reductions for the entire population: zealotry or evidence based? Am J Hypertens. 2013 Oct;26(10):1187-90.
- F J He, G A MacGregor. Salt reduction lowers cardiovascular risk: meta-analysis of outcome trials. Lancet. 2011 Jul 30;378(9789):380-2.
- N M Kaplan. The final nail for sodium reduction. Curr Hypertens Rep. 2007 Nov;9(5):349-50.
- N R Cook, JA Cutler, E OBarzanek, J E Buring, K M Rexrode, S K Kumanyika, L J Appel, P K Whelton. Long term effects of dietary sodium reduction on cardiovascular disease outcomes: observational follow-up of the trials of hypertension prevention (TOHP). BMJ. 2007 Apr 28;334(7599):885-8. Epub 2007 Apr 20.
- F Godlee. The food industry fights for salt. BMJ. 1996 May 18;312(7041):1239-40.
- J J DiNicolantonio, P Di Pasquale, R S Taylor, D G Hackam. Low sodium versus normal sodium diets in systolic heart failure: systematic review and meta-analysis. Heart. 2013 Mar 12.
- M Jun, B Neal. Low dietary sodium in heart failure: a need for scientific rigour. Heart. 2014 Nov;100(21):e2.
- P K Whelton, L J Appel, R L Sacco, C A Anderson, E M Antman, N Campbell, S B Dunbar, E D Frohlich, J E Hall, M Jessup, D R Labarthe, G A MacGregor, F M Sacks, J Stamler, D K Vafiadis, L V Van Horn. Sodium, blood pressure, and cardiovascular disease: further evidence supporting the American Heart Association sodium reduction recommendations. Circulation. 2012 Dec 11;126(24):2880-9.
- F J. He, G A MacGregor. Salt Intake and Mortality. Am J Hypertens. 2014 Nov; 27(11): 1424.
- N Graudal, G Jurgens, B Baslund, M H Alderman. Compared with usual sodium intake, low- and excessive-sodium diets are associated with increased mortality: a meta-analysis. Am J Hypertens. 2014 Sep;27(9):1129-37.
- P K Whelton, L J Appel. Sodium and cardiovascular disease: what the data show. Am J Hypertens. 2014 Sep;27(9):1143-5.
- N Graudal, M H Alderman. Response to “Salt Intake and Mortality”. Am J Hypertens. 2014 Nov; 27(11): 1425.
- F J He, S Pombo-Rodrigues, G A MacGregor. Salt reduction in England from 2003 to 2011: its relationship to blood pressure, stroke and ischaemic heart disease mortality. BMJ Open. 2014 Apr 14;4(4):e004549.
- N R Campbell, F P Cappuccio, S W Tobe. Unnecessary controversy regarding dietary sodium: a lot about a little. Can J Cardiol. 2011 Jul-Aug;27(4):404-6.
- N R Cook, L J Appel, P K Whelton. Lower levels of sodium intake and reduced cardiovascular risk. Circulation. 2014 Mar 4;129(9):981-9.
- S Oparil. Low sodium intake--cardiovascular health benefit or risk? N Engl J Med. 2014 Aug 14;371(7):677-9.
- NA. CMJE Form for Disclosure of Potential Conflicts of Interest
- T C Beard. Comment on Editorial about salt intake. Kidney International (2007) 71, 86. doi:10.1038/sj.ki.5001952.
- J Tuomilehto, P Jousilahti, D Rastenyte, V Moltchanov, A Tanskanen, P Pietinen, A Nissinen. Urinary sodium excretion and cardiovascular mortality in Finland: a prospective study. Lancet. 2001 Mar 17;357(9259):848-51.
- H E de Wardener, G A MacGregor. Harmful effects of dietary salt in addition to hypertension. J Hum Hypertens. 2002 Apr;16(4):213-23.
- N R Campbell, D T Lackland, M L Niebylski. 2014 dietary salt fact sheet of the World Hypertension League, International Society of Hypertension, Pan American Health Organization technical advisory group on cardiovascular disease prevention through dietary salt reduction, the World Health Organization collaborating centre on population salt reduction, and World Action on Salt & Health. J Clin Hypertens (Greenwich). 2015 Jan;17(1):7-9.
Images thanks to JD Hancock via Flickr.
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Sodium Skeptics Try to Shake Up the Salt Debate
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Content URLDoctor's Note
This video is part of my extended deep-dive series on sodium, with lots more to come. Here are the ones I put up so far:
- High Blood Pressure May Be a Choice
- Sprinkling Doubt: Taking Sodium Skeptics with a Pinch of Salt
- The Evidence That Salt Raises Blood Pressure
Salt restriction is also important for kidney stones, How to Treat Kidney Stones with Diet, but aren’t low-salt diets tasteless? Only for a little while. See Changing Our Taste Buds
For more on how industry influence can distort nutritional science, see:
- The McGovern Report
- Eggs and Cholesterol: Patently False and Misleading Claims
- Collaboration with the New Vectors of Disease
- Big Sugar Takes on the World Health Organization
- Food Industry Funded Research Bias
- Big Food Using the Tobacco Industry Playbook
- The Healthy Food Movement: Strength in Unity
If you haven’t yet, you can subscribe to my videos for free by clicking here. Read our important information about translations here.