The Nutrition Debate #153: “Salt: friend of foe?”

A recent Lancet article (Volume 381, Issue 9880. 5/25/13), “Salt: friend or foe?” revisits this perennial conundrum. It begins,

“Dietary guidelines advise against the consumption of too much salt. A high intake of sodium causes raised blood pressure – an established risk factor for heart disease, stroke and kidney disease. But how much salt is too much? And could a very low salt intake also be detrimental?”

What was the impetus for this latest foray into the controversial “effects of salt consumption on health outcomes”? The answer: a May 14, 2013 Consensus Report, “Sodium Intake in Populations: Assessment of Evidence” prepared by the Institute of Medicine’s (IOM) “Committee on the Consequences of Sodium Reduction in Populations.” The Centers for Disease Control and Prevention (CDC) asked IOM to do the study since IOM “serves as adviser to the nation to improve health.” Who better, then, to examine the question, right?

The casual observer might not see what’s at play here, but for me the key words are the first two in the lead quote above: “Dietary guidelines”; they are obviously an indirect reference (since “guidelines” is not capitalized) to the most recent “2010 Dietary Guidelines for Americans.” In the Guidelines, the authors at the USDA/HHS call for the general population to have “a goal of reducing sodium intake to less than 2,300mg/day, and further reducing intake to 1,500mg/day” among very large population subgroups including everyone 51 years older and older, all people who have hypertension, diabetes, or chronic kidney disease, and all African Americans.  The American Heart Association (AHA) “even advises that everyone adheres to the 1,500mg/day limit, irrespective of age or race,” according to the Lancet article.

I won’t keep you in suspense any longer. What are the “implications for population-based efforts” at dietary guidelines for sodium consumption? According to the IOM, the “assessment of evidence” of “sodium intake in populations,” is as follows:

·         The available evidence on associations between sodium intake and direct health outcomes is consistent with population-based efforts to lower excessive dietary sodium intakes.

·         The evidence on health outcomes is not consistent with efforts that encourage lowering of dietary sodium in the general population to 1,500mg/day.

·         There is no evidence on health outcomes to support treating population subgroups differently from the general U.S. population.

Alright, I won’t quarrel with the first conclusion. “Excessive dietary sodium intakes” are obviously…well, “excessive.” We are all told how processed and prepared foods are loaded with hidden salt, especially soup, right? The solution: Don’t buy or eat processed or prepared foods. Eat only “real” food – whole foods – and add salt to your taste.

The second conclusion is startling and really troubling. Lowering dietary sodium in the general population to 1,500mg/day, as the American Heart Association purportedly recommends, is not consistent with the evidence? And this a principal conclusion from a distinguished committee at the Institute of Medicine? What do they say to support this conclusion?

“…(T)he committee concludes that the evidence supports a positive relationship between higher levels of sodium intake and risk of CVD. This is consistent with existing evidence on blood pressure as a surrogate indicator of CVD and stroke risk for the general population. The committee also concludes that studies on health outcomes are inconsistent in quality and insufficient in quantity to determine that sodium intakes below 2,300mg/day either increase or decrease the risk of heart disease, stroke, or all-cause mortality in the general U.S. population.”

Wow. But how about those “special population” subgroups that taken in their entirely make up a majority of the adult population of the United States. Is there really “no evidence to support treating population subgroups differently…”? Here’s what the IOM committee, examining this specific question, said about that:

“The committee found no evidence for benefit and some evidence suggesting risk of adverse health outcomes associated with sodium intake levels in ranges approximately 1,500 to 2,300mg/day among those with diabetes, kidney disease, or CVD. Further, the evidence on both the benefit and harm is not strong enough to indicate that these subgroups should be treated differently than the general U.S. population. Thus, the evidence on direct health outcomes does not support recommendations to lower sodium intake within these subgroups to or even below 1,500mg/day.” (emphasis mine)

Okay, you say this is just an internecine quarrel between government agencies, pitting the medical (AHA), public health (HHS) and agribusiness (USDA) establishments against the less influential CDC and IOM. In fact, if you hadn’t read this Lancet article about an obscure IOM report here, it is not likely you would have read about it anywhere else. IOM and CDC don’t get much notice in the popular press regarding American dietary choices. But, there has been and will be plenty of talk in the blogosphere. My post #74, “No Added Salt? Why?,” had 5 links to good sources on salt in the diet: here, for Gary Taubes’s “The (Political) Science of Salt” from 1998 and here for his 2012 NYT op-ed “Salt, We Misjudged You”; this from a stunning 2011 article in Diabetes Care about a University of Melbourne study; this Chris Kresser article, “The Dangers of Salt Restriction” about a 2011 study reported in JAMA; and this from the Drs. Michael and Mary Dan Eades of “Protein Power.”