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Salt Intake Set by the Brain
Study explains why official advice goes unheeded … and may be unhealthful for many
9/26/2013By Craig Weatherby
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U.S. health authorities have long urged limits on people’s salt intake.
 
This advice stemmed from studies showing that blood pressure often drops slightly when people eat less salt, with greater pressure drops seen in certain subgroups.
 
So it seemed logical to urge people to cut back on sodium to reduce the risks of high blood pressure, which promotes cardiovascular disease and stroke.
 
The U.S. dietary guidelines for 2010 recommend these daily intakes:
  • 2,300mg or less – General population.
  • 1,500mg daily (half a teaspoon of salt) maximum – People aged 51 or older, African-Americans, and people with hypertension, diabetes, or chronic kidney disease.
Last May, the U.S. Institute of Medicine (IOM) issued a report that upset conventional wisdom.
 
The IOM’s sodium panel looked at the evidence and saw little to support standard sodium-intake advice … see “Salt Exonerated (Mostly) by U.S. Experts”.
 
Doubts about advice on sodium date back more than 10 years, as we reported in “Take New Sodium Advice with a Grain of Salt”.
 
In fact, the data show that heart patients with intakes below 3,000mg daily could be doing themselves more harm than good.
 
The increased risks seen with daily sodium intakes below 3,000mg include greater risk of death and heart attack (Paterna S et al. 2008; Paterna S et al. 2009; O'Donnell MJ et al. 2011; Stolarz-Skrzypek K et al. 2011).
 
Now, an international team’s report further undermines the idea that people can – or should try to – stick to official guidelines.
 
Salt intake set by the brain
The new study comes from researchers at UC Davis, Harvard Medical School, Seattle’s Bastyr University, and Copenhagen’s University Hospital, Rigshospitalet.
 
Its results echo what neuroscientists find true about animals … that sodium (salt) intake is controlled by networks in the brain.
 
And they affirm prior evidence that people unconsciously maintain daily sodium intakes within a relatively narrow range … with the lowest intakes being higher than the official guideline (2,300mg).
 
The authors analyzed data from studies covering more than 69,000 people in 45 countries over the past 50 years.
 
In each of the 190 studies they analyzed, researchers measured participants’ sodium intake by measuring the amount excreted in urine during a 24-hour period.
 
The analysis showed an average sodium intake of about 3,650 mg per day, and a range of 2,600 to 4,800 mg per day.
 
As lead author David McCarron, M.D., said, “Our data clearly demonstrate that humans’ sodium (salt) intake is regulated within a relatively narrow ‘normal’ range that is defined by the body’s physiology and biological need rather than by the food supply.” (UCD 2013)
 
“This analysis defines the normal range and mean [average] value for sodium intake in humans and documents that the range has not changed during five decades, nor been influenced by ethnicity or the unique dietary practices of various cultures around the world,” he added (UCD 2013).
 
Findings suggest official policies lack credibility or purpose
Drawing a reasonable conclusion, Dr. McCarron said, “The nation’s future health policies and guidelines should be developed based on that biologically determined range. Our data demonstrate that past U.S. guidelines for sodium (salt) intake are well below human needs.” (UCD 2013)
 
Co-author Joel Geerling, M.D. of Harvard Medical School underscored the reason why sodium intake appears remarkably consistent across decades, ethnicities, and regions:
“These findings are consistent with the idea that eating salt is physiologically controlled, as predicted by decades of efforts … directed at understanding the brain’s role in the regulation of sodium appetite.” (UCD 2013)
 
“Our new study explains why decades of government efforts have failed to lower the sodium, or salt, intake in the U.S.,” said co-author Judith Stern, professor emeritus of nutrition and internal medicine at UC Davis (UCD 2013).
 
“Policy simply cannot change physiology. If future nutritional guidelines are to be effective, they must be based on the scientific reality reflected in these data, which have documented that a normal range for human sodium intake exists,” she said.
 
“Sodium intake will not be changed by altering the salt content of food products or other public-policy attempts to limit sodium consumption.”
 
Funding for the study did not come from the food industry, nor did any of the researchers report conflicts of interest.
 
 
Sources
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  • Dahl LK. Sodium intake of the American male: implications on the etiology of essential hypertension. Am J Clin Nutr. 1958 Jan-Feb;6(1):1-7
  • Freedman DA, Petitti DB. Salt and blood pressure. Conventional wisdom reconsidered. Eval Rev. 2001 Jun;25(3):267-87. Review.
  • McCarron DA, Drüeke TB, Stricker EM. Science trumps politics: urinary sodium data challenge US dietary sodium guideline. Am J Clin Nutr. 2010 Nov;92(5):1005-6. Epub 2010 Oct 6.
  • McCarron DA, Kazaks AG, Geerling JC, Stern JS, Graudal NA. Normal range of human dietary sodium intake: a perspective based on 24-hour urinary sodium excretion worldwide. Am J Hypertens. 2013 Oct;26(10):1218-23. doi: 10.1093/ajh/hpt139. Epub 2013 Aug 26.
  • O'Donnell MJ, Yusuf S, Mente A, Gao P, Mann JF, Teo K, McQueen M, Sleight P, Sharma AM, Dans A, Probstfield J, Schmieder RE. Urinary sodium and potassium excretion and risk of cardiovascular events. JAMA. 2011 Nov 23;306(20):2229-38. doi: 10.1001/jama.2011.1729.
  • Paterna S, Gaspare P, Fasullo S, Sarullo FM, Di Pasquale P. Normal-sodium diet compared with low-sodium diet in compensated congestive heart failure: is sodium an old enemy or a new friend? Clin Sci (Lond). 2008 Feb;114(3):221-30.
  • Paterna S, Parrinello G, Cannizzaro S, Fasullo S, Torres D, Sarullo FM, Di Pasquale P. Medium term effects of different dosage of diuretic, sodium, and fluid administration on neurohormonal and clinical outcome in patients with recently compensated heart failure. Am J Cardiol. 2009 Jan 1;103(1):93-102. doi: 10.1016/j.amjcard.2008.08.043. Epub 2008 Oct 17.
  • Report of the Dietary Guidelines Advisory Committee on the Dietary Guidelines for Americans, 2010. June 15, 2010. Accessed at http://www.cnpp.usda.gov/DGAs2010-DGACReport.htm
  • Stolarz-Skrzypek K, Kuznetsova T, Thijs L, Tikhonoff V, Seidlerová J, Richart T, Jin Y, Olszanecka A, Malyutina S, Casiglia E, Filipovský J, Kawecka-Jaszcz K, Nikitin Y, Staessen JA; European Project on Genes in Hypertension (EPOGH) Investigators. Fatal and nonfatal outcomes, incidence of hypertension, and blood pressure changes in relation to urinary sodium excretion. JAMA. 2011 May 4;305(17):1777-85. doi: 10.1001/jama.2011.574.
  • The New York Times. No Benefit Seen in Sharp Limits on Salt in Diet. May 14, 2013. Accessed at http://www.nytimes.com/2013/05/15/health/panel-finds-no-benefit-in-sharply-restricting-sodium.html
  • University of California, Davis (UCD). Salt intake physiologically set in humans, new study finds. August 26, 2013. Accessed at http://news.ucdavis.edu/search/news_detail.lasso?id=10692
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