How Much Salt?
July 5, 2015
Jacob Schor, ND, FABNO
www.DenerNaturopathic.com

In the practice of medicine, we advocate for rational, objective, unbiased decision making that favors the best interests of our patients. At least that is what we all claim. Yet the reality is often different and practitioners often fragment into different camps adhering to one side or another of debates regarding specific practices. Far from being dispassionate and objective arbiters of the science, we often take sides and defend our beliefs in a manner that is far from dispassionate. Rather, our behavior is more akin to one defending a belief or faith rather than working their way toward rational advancement of knowledge

These thoughts are prompted by the ongoing debate over how much salt people should eat. Or more accurately stated, how much salt we, as physicians, should tell people to eat, or actually, not eat. Most people eat plenty of salt and our job is supposed to be to tell them to eat less of it.

This ‘salt debate’ and the intensity of the positions taken is worth watching, not just because it would be useful for us to know what to tell our patients but also to watch the process unfold, for battle lines to be drawn and to witness how quickly supposedly rational people lose hold of their objectivity. Knowledge keeps changing and to practice good medicine, our understanding of what is ‘right’ must change and evolve with the science. This does not come easily for many of us. Thus watching this evolution of thinking regarding salt, may help us learn to adapt in other areas of science as well.



The idea that the public should limit sodium intake through reductions in dietary salt intake was introduced in 1972 when the National Institutes of Health started the National High Blood Pressure Education Program. At the time, available evidence to support such a recommendation was weak. The problem now is that nearly half a century later, the evidence is still weak; it seems that the suggestion to limit salt has been so often repeated over the years, that most people, patients and doctors, just assume the idea is well proven.

Regardless of the evidence or lack thereof, the NIH’s and the American Heart Association’s position about sodium remains strong; reading their position statements, one would assume that the evidence was solid:

“This evidence is extensive [1] ---- from clinical therapeutics, animal experimentation, physiology and pathophysiology, cross population and within population epidemiologic research, anthropology and randomized controlled trials.” [2]
From: Implementing Recommendations for Dietary Salt Reduction 1996

Yet, according to Gary Taubes, writing in the New York Times, “….the U.S.D.A., the Institute of Medicine, the C.D.C. and the N.I.H. — all essentially rely on the results from a 30-day trial of salt, the 2001 DASH-Sodium study. [3] It suggested that eating significantly less salt would modestly lower blood pressure; it said nothing about whether this would reduce hypertension, prevent heart disease or lengthen life.”[4] 

Actually the Institute of Medicine has backtracked fromn their sodium position releasing a position paper in May 2013 suggesting that current evidence “is not consistent with efforts that encourage lowering of dietary sodium in the general population to 1,500 mg/day.” [5] 

Our need for salt is a fundamental evolutionary inheritance, a reminder that our ancestors were once ocean dwellers. Our cells still require salt concentrations reminiscent of our past. We cannot survive without minimal levels of salt in our blood that are similar to sea water. T
he idea that excess salt is harmful is not unreasonable. High salt consumption causes the body to retain water in order to maintain a constant sodium concentration in the blood. Salty foods make us thirsty, we drink more water and for a short period, blood pressure increases until the kidneys excrete the excess salt and water. As high blood pressure is a risk factor for cardiovascular disease (CVD), the idea that chronic blood pressure increases caused by high salt consumption over time would increase CVD is reasonable. The problem again is that there has been little evidence to support this idea. 

Jordi Salas-Salvadó, the principal author of a recent study pointed out that while the “2010 US Dietary Guidelines for Americans recommended a sodium intake below 2300 mg per day [~1 teaspoon of salt] in the general population. …. it is unknown whether decreasing sodium intake below 2300 mg/d has an effect on CVD or all-cause mortality. The recent Institute of Medicine (IOM) explicitly concluded that studies on health outcomes are inconsistent in quality and insufficient in quantity to determine that sodium intake below 2300 mg/d may increase or decrease the risk of heart disease, stroke or all cause of mortality.” [6] 


In 2014, a Cochrane Review failed to confirm the current government recommendations. Eight studies were included in the review: three of the studies were on people with normal blood pressure (n= 3,518), while the other five studies had mixed populations of normal and hypertensive participants (n=3,766). There was no significant change in risk of mortality for people with normal blood pressure associated with low salt intake [RR 0.67, 95% confidence interval (CI) 0.40 - 1.12]. There was a non-significant trend toward lower cardiovascular disease related mortality in participants with high blood pressure who lowered salt intake [RR 0.67, 95% CI 0.45 - 1.01].[7]

A September 2014 meta-analysis by Niels Graudal of Denmark really brought the issue into question. Graudal looked at all cause mortality and CVD in populations exposed to varying amounts of sodium. Data from 23 cohort studies and 2 follow up RCTs (n=274,683) showed that risk of mortality or CVD events was about 10% lower in people consuming what the researchers considered a normal amount of sodium [115-165 mmol/day (6728-9653 mg salt or 2 ¾ tsp to 4 tsp/day)] compared to low sodium intake (<115 mmol < 6728 mg salt or < 2 3/4 tsp)). Risk of mortality increased about 16% and for CVD events by about 12 % in people consuming large amounts of sodium (> 215 mmol 12,578 mg salt or 5 ¼ tsp salt/day). [8] In other words following the NIH’s current suggestion of consuming less than a teaspoon of salt per day was associated with increased mortality and CVD events compared to rather liberal salt use. Thus in Grudal’s view, "For most people, there is no reason to change their dietary habits concerning salt, as most people eat what appears to be the safest amount." [9] 

Just as a reminder, the 2010 Dietary Guidelines for Americans that recommend a sodium intake below 2300 mg per day (equivalent to just less than 1 teaspoon of salt per day) for the general population.

These USDA Dietary Guidelines rank salt as one of the most dangerous aspects of the American Diet, at the top of their list of harmful foods, listing salt even before “… solid fats, added sugars and refined grains….” [10]

Yet is it as dangerous as the USDA would have us believe? Most important, does complying with the USDA’ guideline to eat less than 2300 mg per day have long term benefits?

Suggestions that these guidelines might be a bit too conservative have over the years met with a strong backlash. Back in 2006, the Journal of the College of Nutrition published a supplemental issue focusing on various issues related to salt and that raised the issue that the guidelines might be too low.

The Center for Science in the Public Interest (CSPI) attacked the journal almost immediately accusing them of ethical violations, of misrepresenting the science, of allowing Frito-Lay and other junk food manufacturers to influence them. [11] This was an important enough accusation that Science News had Janet Raloff, one of their senior editors, investigate the controversy in great deal and report on it. In the end it seems as if CSPI’s accusations were for the most part unfounded; rocking the boat and questioning the status quo isn’t easy. [12 

In a March 2015 paper, Salas-Salvadó attempted to answer the salt question. He and colleagues who have been part of the PREDIMED group used their earlier data to compare sodium intake from food frequency questionnaires to look for an association between incidence of CVD events and mortality with lower sodium consumption. Recall that the 3,982 participants in the PREDIMED cohort were all at high risk for cardiovascular disease. 

Participants were categorized by sodium intake as low (<1500 mg/d), intermediate (≥1500 to ≤2300 mg/d), high (>2300 to ≤3400 mg/d), or very high (>3400 mg/d).
Deaths and CVD events were measured for a median of 4.8 years. Sodium intake <2300 mg/d was associated with a 48% lower risk of all-cause mortality after one year and 49% decrease risk after 3 years. Increasing sodium intake after 1 year was associated with a 72% higher risk of CVD events. 

On the face of this evidence, this study is strong support for the low-sodium side.[13] Yet recall that this study involved the PREDIMED Trial Cohort, all of who were at high risk for heart disease; just over 70% were already medicated for hypertension. [14] Only about 51% of hypertensive people are salt sensitive but for them, reducing dietary salt intake will help reduce blood pressure. [15] On the other hand, reducing salt intake in someone with normal blood pressure does not lower blood pressure and may not offer the same health benefit. Given that more than half of the PREDIMED cohort had high blood pressure, it is possible that low salt diets offered them a benefit not seen for the general population. Thus the findings of this study may not really conflict with the results reported in the Graudal and Cochrane Reviews. 

Robert Heaney, a well known endocrinologist specializing in nutrition and a professor at Creighton University, best known for his work on osteoporosis and vitamin D, startled many with an article published in the March/April 2015 issue of Nutrition Today. His analysis of the available evidence led him to conclude that health risks increase when sodium intake drops below 3-4 grams per day or if it rises above 6-7 g/day. (2.5 tsp). [16] [this review is worth reading] 

Of course such a suggestion is nutritional sacrilege and Cheryl Anderson, and other mainstream low salt advocates offered a rebuttal in the same issue of Nutrition Today, suggesting that the methodology of the studies Heaney quoted is flawed. [17] 

What will be the final outcome of these salt debates? It may be too early to tell. As a naturopathic physician, I admit my own bias to favor the underdog, my tendency to be drawn to the ‘alternative viewpoint’, to want the mainstream science to be proven wrong. At this point though, it’s too early to tell. 

Likely, as is often the case, the biology may prove more complex than we at first thought. Salt reduction may prove valuable for some, less so for others, and maybe harmful for others. Learning to determine who and when to apply salt restriction to, will become another aspect to our art of practice. In the meantime, the real lesson is in watching the participants of this ongoing debate and ask, who is practicing good science and good medicine and who is acting merely to defend a belief system whose foundation is not as solid as we once assumed?



NOTE:
Conversion of salt units:
Any discussion about ideal salt intake are confused by the variety of units used to consumption. Conversion factors are below. In my commentary above all amountshave been reported into teaspoons of salt rounded to the nearest ¼ tsp. 
1 mmol sodium = 23 mg sodium
• 1 g sodium = 43.5 mmol sodium
• 1 g salt (sodium chloride) = 390 mg sodium
• 1 tsp salt = 6 g salt ≈ 2,400 mg sodium = 104 mmol sodium = 104 mEq sodium
To convert mmol to mg of sodium, chloride, or sodium chloride, multiply mmol by 23, 35.5, or 58.5 (the molecular weights of sodium, chloride, and sodium chloride), respectively.
http://www.cdc.gov/salt/sodium_toolkit.htm

References:

1. Cutler JA, Kotchen TA, Obarzanek E (guest eds). The National Heart, Lung, and Blood Institute Workshop on Salt and Blood Pressure. Hypertension 1991;17:I1-121.

2. https://www.nhlbi.nih.gov/files/docs/resources/heart/hbp_salt.pdf National High Blood Pressure Education Program: Implementing Recommendations for Dietary Salt Reduction. NIH. Publication No. 55-728N, Nov 1996. 

3 Vollmer WM, Sacks FM, Ard J, Appel LJ, Bray GA, Simons-Morton DG, Conlin PR, et al. DASH-Sodium Trial Collaborative Research Group. Effects of diet and sodium intake on blood pressure: subgroup analysis of the DASH-sodium trial. Ann Intern Med. 2001 Dec 18;135(12):1019-28.

4. Taubes G. Salt, We Misjudged You. New York Times. June 2, 2012.
http://www.nytimes.com/2012/06/03/opinion/sunday/we-only-think-we-know-the-truth-about-salt.html?_r=1

5. http://iom.nationalacademies.org/~/media/Files/Report%20Files/2013/Sodium-Intake-Populations/SodiumIntakeinPopulations_RB.pdf

6. http://medicalresearch.com/heart-disease/much-salt-intake-recommended-patients-heart-disease/10200/

7. Adler AJ, Taylor F, Martin N, Gottlieb S, Taylor RS, Ebrahim S. Reduced dietary salt for the prevention of cardiovascular disease. Cochrane Database Syst Rev. 2014 Dec 18;12:CD009217. 

8. Graudal N, Jürgens 2, Baslund B, Alderman MH. Compared with usual sodium intake, low- and excessive-sodium diets areassociated with increased mortality: a meta-analysis. Am J Hypertens. 2014 Sep;27(9):1129-37. 

9. Reinberg S. CDC salt guidelines too low for good health. HealthDay News, April 2, 2014.
http://www.webmd.com/food-recipes/20140402/cdc-salt-guidelines-too-low-for-good-health-study-suggests

10. http://www.cnpp.usda.gov/sites/default/files/dietary_guidelines_for_americans/ExecSumm.pdf

11. http://www.cspinet.org/new/pdf/jacn_letter_1.pdf

12. https://www.sciencenews.org/blog/food-thought/salty-controversy-over-sodium-and-health-papers

13. Merino J, Guasch-Ferré M, Martínez-González MA, Corella D, Estruch R, Fitó M, Ros E, Salas-Salvadó J, et al. Is complying with the recommendations of sodium intake beneficial for health in individuals at high cardiovascular risk? Findings from the PREDIMED study. Am J Clin Nutr. 2015 Mar;101(3):440-8.

14. Guasch-Ferré M, Bulló M, Martínez-González MÁ, Ros E, Corella D, Estruch R, Fitó M, Arós F, et al; PREDIMED study group. Frequency of nut consumption and mortality risk in the PREDIMED nutrition intervention trial. BMC Med. 2013 Jul 16;11:164.doi:10.1186/1741-7015-11-164.

15. Armando I, Villar VA, Jose PA. Genomics and Pharmacogenomics of Salt-sensitive Hypertension. Curr Hypertens Rev. 2015;11(1):49-56.

16. Robert P. Heaney. Making Sense of the Science of Sodium. Nutr Today. 2015 March; 50(2): 63–66. Published online 2015 March 26.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4420255/pdf/nt-50-66.pdf

17. Anderson CA, Johnson RK, Kris-Etherton PM, Miller EA. Commentary on Making Sense of the Science of Sodium. Nutr Today. 2015 Mar;50(2):66-71.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4420255/