A broad group of international experts are recommending a far more modest and less draconian approach to sodium restriction than current U.S. and international guidelines.
In a new paper, , they also focused on the broad gaps of knowledge in the field and drew attention to the paucity of high-quality evidence and research. Again, this approach represented a rebuke of current guidelines, which authoritatively assert the benefits of dramatic reductions in salt consumption.
Worldwide, sodium intake is estimated to average about 3.95 g/day, though there are wide geographical and cultural variations. Most guidelines recommend that sodium consumption be reduced to levels below 2.3 g/day, though the American Heart Association goes further and recommends reductions to 1.5 g/day or lower.
By contrast, the authors of the new paper recommended that sodium be reduced to under 5 g/day, since "there is consistent evidence that high sodium intake (> 5 g/day) is associated with increased CV risk." However, they freely acknowledged that there is no good randomized, controlled trial evidence to support this target. And they explicitly rejected the lower target of other guidelines, explaining that "there is an ongoing scientific debate about the optimal lower level of sodium intake for CVD prevention."
The new paper also emphasized the potential dangers of lowering sodium too much, as in the WHO and AHA guidelines. "Sodium," the authors wrote, "is an essential nutrient. This implies that there must be a 'U'-shaped relationship between dietary sodium intake and cardiovascular events, but there is no consensus of where the minimum risks lies."
An Internal Rebellion
The paper in some respects reflected an internal rebellion within the international hypertension, nutrition, and public health establishment against the extreme recommendations promulgated by the AHA, WHO, and other organizations. For this reason, and in order to prevent a public rupture within the expert community, the paper was labelled as a "technical report" from the "joint working group of the World Heart Federation, the European Society of Hypertension and the European Public Health Association." Ostensibly, the paper was about sodium in low- and middle-income countries, but the vast majority of the paper applied to high-income countries as well.
Because it is labelled as a "technical report," several of the authors explained to me, it did not require endorsements or approval from the hundreds of individual organizations represented by the working group. Endorsements from many of the groups would be nearly impossible to obtain, given that many have already endorsed one form or another of the extreme sodium restrictions.
The full title of the paper is "The technical report on sodium intake and cardiovascular disease in low- and middle-income countries by the joint working group of the World Heart Federation, the European Society of Hypertension and the European Public Health Association." Among the authors of the report are well-known hypertension experts like Giuseppe Mancia, Suzanne Oparil, and Paul Whelton.
"We all agree that populations that consume large amounts of salt have more deaths and cardiovascular events than populations using lesser amounts," said co-author, Michael Weber (SUNY Downstate College of Medicine). "But anything more subtle than that is problematic." The AHA recommendation "is not strongly evidence-based."
In sharp contrast to the guidelines, the "technical" paper called attention to the many limitations in the field that make firm, detailed guidelines difficult to establish. The paper noted that it is extremely difficult to reliably measure sodium intake in both individuals and in large populations and it is even more difficult to perform large, long-term randomized controlled trials with cardiovascular endpoints.
"While guidelines may recommend an intake of sodium < 2.3 g/day, this target is relatively meaningless to both clinician and patient, as it is not supported by an available objective measurement," they wrote.
Weber said that "the impetus was the lack of credible evidence in the sodium domain. Most published studies are weak, mainly because of the major difficulty of measuring salt intake in individuals ... virtually every study is questionable or even flawed."
Even if lower levels were proven to be beneficial, the experts pointed out that there is no evidence that it would be possible to achieve these low levels in an entire population. "Despite recommendations for population-wide low sodium intake, it has not been shown that sustained low sodium intake is feasible in free living individuals," they wrote.
The Low Sodium Empire Strikes Back
Hardcore defenders of strict sodium guidelines were not convinced by the new paper. Sidney Smith, a member of the committee writing the new ACC/AHA hypertension guideline, said that "there is no new evidence in the paper to support a change from the 2013 recommendations in the ACC/AHA guidelines for the USA (derived from the systematic evidence reviews at NHLBI)."
Rose Marie Robertson, chief science and medical officer of the American Heart Association, tried to minimize the difference between the working group report and the AHA position. "We're in agreement with them about most of the content." She pointed out that the working group report is "consistent" with the AHA position in that it does not question the relationship between lowering sodium and lowering blood pressure, and that both groups agree that lowering blood pressure is an important priority.
Because it's extremely difficult to perform the large trials that would "connect the dots" -- showing that lowering sodium leads to lower blood pressure that then leads to fewer cardiovascular events -- Robertson said it would be "irresponsible to not try to improve the current situation." She said the AHA position makes "biological sense" and that "people want to know what to eat now."
I asked Robertson whether she was concerned that the low-sodium recommendation might have unintended consequences, along the lines of the negative effect of the AHA's earlier recommendations against dietary cholesterol and saturated fat. She said that the AHA and other experts have learned this lesson and are monitoring health statistics and trends. We are "watching these things like a hawk," she said.
Call For Research
At first glance the working group paper's call for more research to inform guidelines may appear unimportant, because the vast majority of published scientific papers reach similar conclusions. But this call becomes far more than a cliché in this context. It is increasingly becoming clear that firm, authoritative guidelines may serve to hinder important research.
Mancia, the lead author of the working group paper, discussed "the potentially negative impact guidelines may have on future research if they issue strong recommendations in areas in which evidence is weak. This discourages potential sponsoring institutions and investigators to engage in further studies, not to mention the risk to have a project rejected by Ethical Committees that may regard the research not needed because the answer is already in the guidelines."
The working group paper "is really a plea for more rigorous methodology in clinical research studies," added Weber. "Once we get credible evidence we can move on to supportable guidelines and recommendations. But this is probably several years away."