References on food salt & health issues
There are two issues that require public policy response: 1) ensuring adequate iodine nutrition to populations around the world and 2) resolving whether populations would be healthier if they consumed a maximum amount of dietary salt (or sodium) and, if so, how to accomplish such salt reduction.
Salt and iodine deficiency
Public health authorities around the world agree on the critical priority need to avoid iodine defiency and the brain damage that results from inadequate iodine consumption. Virtually all agree that universal salt iodization should remain the primary strategy.
Iodine deficiency is the single greatest cause of preventable mental retardation. The problem is explored comprehensively in Basil Hetzel's book Towards the Global Elimination of Brain Damage due to Iodine Deficiency , available online on the website of the International Council for the Control of Iodine Deficiency Disorders (ICCIDD) which he co-founded.
The ICCIDD has the longest focused leadership role in identifying the issue and promoting solutions, primarily through universal salt iodization (USI). The Salt Institute is a long-term supporter. The solutions recommended by ICCIDD involve several essential elements, each well discussed on the ICCIDD website :
- Identifying the need
- Fortifying salt
- Building coalitions , both national and global
- The ICCIDD's quarterly IDD Newsletter is the foremost source of ongoing information.
The Network for the Sustained Elimination of Iodine Deficiency was created by 12 groups (including the Salt Institute) in the aftermath of a major programatic effort at the 8th International Symposium on Salt (Salt2000). The Network's website is another rich source of information about the global campaign against IDD. The Network produces a useful Global Scorecard of the progress against IDD.
Other IDD Network partners have important online resources about iodine deficiency and efforts to overcome IDD. These include:
United Nation's Childen's Fund (UNICEF). UNICEF has provided key support for the effort (with tremendous voluntary contributions gathered by Kiwanis International , another partner) and tracks progress . UNICEF Deputy Executive Director Kul Gautam delivered an outstanding charge in October 2007 to the American Thyroid Association entitled "A public health triumph in the making " which captured the moral imperative of universal salt iodization and included an outstanding historical review of the entire issue. UNICEF has also collected valuable information on technical questions involved in producing iodized salt .
World Health Organization (WHO). WHO also tracks iodine status globally , working through national health ministries. WHO is pursuing both USI and salt reduction having ruled them compatible and is conducting a test of using iodized salt in bread in Poland that will run until 2012.
Global Alliance for Improved Nutrition (GAIN). Funded by the Bill & Melinda Gates Foundation, GAIN works in high-priority countries .
EuSalt -- the Salt Institute's counterpart salt industry association in Europe is dealing with surprisingly resistant problems of iodine deficiency throughout the continent.
The (US) Centers for Disease Control and Prevention (CDC). CDC has taken a leadership role in discovering a disturbing decline in iodine sufficiency status in the United States (in this regard, see the May 2006 ICCIDD IDD Newsletter which contains an excellent article on page 4 on the current status of iodine nutrition in the U.S . by Dr. Elizabeth Pearce of the Boston University School of Medicine). CDC has led development of an international consortium of laboratories throughout the world. CDC has also investigated multiple fortification of salt .
The Micronutrient Initiative (MI). MI has provided hands-on technical support for small salt producers' efforts to iodize salt and pioneered work on double-fortifying salt with iodine and iron (to combat anemia).
Although often promoted as a more healthful alternative to refined table salt, natural sea salt has little iodine and is a poor choice for those concerned about ensuring their iodine sufficiency. Two studies have examined this question carefully:
- Fisher and L'Abbe (1980) tested non-iodized sea salt and iodized table salt and sea salt. The authors found 52.9 - 84.6 micrograms iodine/gram of salt in iodized salt and 1.2 - 1.4 micrograms iodine/gram in non-iodized sea salt. [see Fisher, Peter W. F. and Mary L'Abbe. 1980. Iodine in Iodized Table Salt and in Sea Salt . Can. Inst. Food Sci. Technolo. J. Vol. 13. No. 2:103-104. April]
- Aquaron (2000) determined iodine content of natural sea salt and rock salt, and iodized salt. The author found iodine levels of less than 0.71 milligrams iodine/kilogram of salt (micrograms/gram) in non-iodized salt and 7.65 - 100 mg iodine/kg of salt in iodized salt (depending on the country's iodine laws). [see Aquaron, R. 2000. Iodine content of non iodized salts and iodized salts obtained from the retail markets worldwide. 8th World Salt Symposium . Vol. 2:935-940]
Population health advisories should be evidence-based. We insist that pharmacologic interventions be justified as "safe and efficacious." That should be our expectation for non-pharmacologic interventions as well. The public is bombarded with messages that seem to change with every issue and every edition. Some of this reflects the natural progression of science, but much of it comes from uncritical reporting, even by prestigous medical journals. The way forward is found in evidence-based medical and public health policy-making.
The Cochrane Collaboration invented the concept and describes it with authority. These are key references:
- About the Cochrane Collaboration
- BMJ editorial on "Evidence-based medicine; what it is and what it isn't " by David Sackett et al for the Cochrane Collaboration
Cochrane Reviews on salt and health
- Hooper et al, "Advice to reduce dietary salt for prevention of cardiovascular disease " (Cochrane Review) – The Cochrane Library Issue 1, 2004
- Hooper, et al, "Systematic review of long term effects of advice to reduce dietary salt in adults ," BMJ vol 325 21 Sept 2002
- Jürgens G, Graudal NA, "Effects of low sodium diet versus high sodium diet on blood pressure, renin, aldosterone, catecholamines, cholesterols, and triglyceride " (Cochrane Review)
- Graudal, et al, "Effects of Sodium Restriction on Blood Pressure, Renin, Aldosterone, Catecholamines, Cholesterols, and Triglyceride A Meta-analysis ," JAMA. 1998;279:1383-1391.
- And see this lay version by Niels Graudal: "Effect of salt intake on blood pressure and cardiovascular outcome: critical evaluation of reported trials and meta-analyses " published by the Salt Association (UK).
In the U.S., the U.S. Preventive Services Task Force (HHS Agency for Healthcare Research and Quality) provides "Counseling to promote a healthy diet " examining the various claimed associations of dietary variables to health outcomes
Other key studies of the health outcomes of reduced-salt diets
Michael H. Alderman, "Salt, Blood Pressure, and Cardiovascular Disease ," Presidential address, International Society of Hypertension (37-minute video with slides)
Midgley, et al, "Effects of Reduced Dietary Sodium on Blood Pressure - A Meta-analysis of Randomised Controlled Trials ," JAMA, May 1996
Alderman, et al, "Dietary sodium intake and mortality: the National Health and Nutrition Examination Survey (NHANES I) ." The Lancet (vol 351 . March 14, 1998)
Cohen, et al, "Sodium Intake and Mortality in the NHANES II Follow-up Study ," American Journal of Medicine, Volume 119, Issue 3, Pages 275.e7-275.e14 (March 2006)
Cohen, et al "Sodium Intake and Mortality Follow-Up in the Third National Health and Nutrition Examination Survey (NHANES III) ," Journal of General Internal Medicine, Volume 23, Number 9 / September, 2008
Fodor, et al, "Recommendations on dietary salt ," Canadian Medical Association Journal. May 4,1999;160 (9 Suppl), pages S29-S34.
David A. McCarrron, "The dietary guideline for sodium: should we shake it up? Yes! " American Journal of Clinical Nutrition, 2000;71:1013-9.
Geleijnse et al, "Sodium and potassium intake and risk of cardiovascular events and all-cause mortality: the Rotterdam Study ," European Journal of Epidemiology, (2007) 22:763–770.
Tunstall-Pedhoe et al "Comparison of the prediction by 27 different factors of coronary heart disease and death in men and women of the Scottish heart health study: cohort study ," BMJ 1997;315:722-729 (20 September)
Alderman et al, "Low Urinary Sodium Is Associated With Greater Risk of Myocardial Infarction Among Treated Hypertensive Men ", Hypertension, 1995;25:1144-1152.
Controlled trial needed
As the Cochrane Collaboration and U.S. Preventive Services Task Force agree, there is insufficient evidence of a health benefit for low-sodium diets. As evidence from three studies of the NHANES database for the U.S. and independent studies in Scotland and the Netherlands note, there is either an absence of cardiovascular health benefits for those on lower sodium diets -- or an actual increase in risk for those following the recommendation to reduce dietary salt. A controlled trial is required as has been noted by researchers and such groups as the Salt Institute and Grocery Manufacturers of America ("Sodium and Salt " January 2009). Fortunately, the federal government has a lot of experience with health outcomes studies. It conducted a major study of the health benefits of anti-hypertensive medications -- the ALLHAT Study -- during which study one class of drugs was dropped from the study because, while it reduced blood pressure just as predicted, it wasn't improving health outcomes. That's the concept for a health outcomes study of salt reduction. And the model for the salt outcomes study is also proven. The salt reduction health outcomes trial can use the approach proven in the Trials of Hypertension Prevention, phase II. See Lasser, et al, (for the Trials of Hypertension Prevention TOHP Collaborative Research Group), "Trials of Hypertension Prevention, Phase II - Structure and Content of the Weight Loss and Dietary Sodium Reduction Interventions ," Annals of Epidemiology, Volume 5, Number 2, March 1995 , pp. 156-164(9)
Still, many governments and public health organizations recommend salt reduction for the entire population, arguing that a hidden reduction of salt in small increments will result in reduced population sodium intake. Though logical, this proposition has never been tested. Research reported in February 2008 in the Experimental Physiology showing a hard-wired "salt appetite" in humans' neural systems would call this thesis into question. See Geerling and Lowey, "Central regulation of sodium appetite ," in Experimental Physiology, 2008, 93.2 pp 177–209
And research confirms that reducing the salt content of some vegetables discourages consumption , contrary to dietary recommendations. The salt masks the bitter flavors of some vegetables like broccoli. See Salt Sensibility blog post "Out of the mouths of babes," May 22, 2007.