In a new challenge to the medical orthodoxy that says reducing sodium consumption is healthy, yet another study has found that low sodium intake is associated with increased rates of heart diseases and death in the general population.

The link applies to those with and without high blood pressure, said the study, published Friday in The Lancet. For those with hypertension, about 11 percent of the population, low as well as high sodium intake is also associated with increased heart disease and death.

The study estimated intake by measuring urinary sodium excretion. It’s available at https://j.mp/lancetsalt.

Data from 133,118 people in 49 countries, 63,559 with hypertension and 69,559 without hypertension, went into the study.


“These data suggest that lowering sodium intake is best targeted at populations with hypertension who consume high sodium diets,” the study concluded.

The issue is important to public health: Is it wise to set a national dietary policy that’s not demonstrated to be medically useful for, or might even harm, nearly 90 percent of the public?

Much the same can be said of the guidelines for fat and cholesterol consumption, also once regarded as proven beyond doubt.

While not proving causality, the Lancet study adds to the latest in a growing body of research finding that universal adoption of low-sodium diets isn’t scientifically supported. This runs contrary to the recommendations of numerous public agencies, medical and activist organizations.


That research, including a 2014 study in the New England Journal of Medicine found that low salt intake is associated with increased risk of major heart problems or death.

(Andrell Bower)

Average sodium intake for Americans is 3,400 to 3,700 milligrams daily, the great majority from salt. The NEJM study found that the average sodium intake of Americans was close to the amount associated with the lowest risk. Below that amount, the risk rose sharply, above it the risk rose more slowly.

Another study published last year in Cell Metabolism found that salt plays an important role in fighting infections.


And a 2013 report by the Institute of Medicine warned of potential harm from too low a sodium intake. The report also declined to endorse calls from public health agencies and the American Heart Association to reduce sodium intake to below 2,300 or 2,400 milligrams a day.

The AHA, for example, recommends that people consume no more than 1,500 milligrams of sodium per day.

While acknowledging that studies opposing the AHA’s advice exist, the association simply dismisses them as flawed in its advice to the public.

The 2013 Institute of Medicine report said there are flaws in the total body of research on the subject, understatedly describing the evidence as “less-than-optimal.”


Moreover, newer studies performed since the IOM report point out a significant danger from low sodium intake, something that public health agencies and medical associations tend to overlook.

Sodium excretion versus adverse events in those with hypertension. The risk profile fits a wide U shape, indicating that too little dietary sodium can be as bad as too much. ( / Mente, et al, The Lancet)

The Lancet study found that for those with hypertension, risk could be represented on a U-shaped curve with those in the middle range of consumption having the least risk.

Moreover, for those without high blood pressure, the risk from high sodium intake was dwarfed by the risk from excessively low intake.


Sodium excretion versus adverse events in those without hypertension. The risk profile indicates a greater danger from consuming too little sodium than from consuming too much. ( / Mente, et al, The Lancet)

An accompanying commentary in The Lancet said the study is the “most persuasive evidence” to date that the blanket recommendations of governments for sodium restriction are not valid.

“It will be contended that randomized controlled trials to determine the intake of sodium on outcome are simply not feasible, and that the benefits of a low-salt-for all strategy outweigh any potentially harmful effects,” the commentary stated. “However, without defining precisely the latter risk, this approach is inherently flawed in that the assumption on which the premise is based is scientifically incorrect.”

The commentary can be found at https://j.mp/lancetsaltcomment.


Opposition

The study was disputed by The Center for Science in the Public Interest, which lobbies the government on nutrition policy. The group, which has labeled salt “perhaps the deadliest ingredient in our food supply,” has long advocated government-mandated limits on food salt content.

CSPI issued a three-paragraph statement contesting the results. The group said the study likely confused cause and effect. In other words, people who were ill ate less, therefore excreted less sodium. The group didn’t present any evidence for that claim.

“Furthermore, the study relies on a single urine sample to estimate the long-term sodium intake of each study’s participants, despite the poor validity of those estimates,” the CSPI press release said. “Studies like the Trials of Hypertension Prevention indicate that when those flaws are avoided, people with the lowest sodium intakes have the lowest risk of cardiovascular events.”


That study, last updated in 2006, did not list reducing cardiovascular events as an objective. It was designed to test several non-drug methods, including sodium reduction to reduce blood pressure in those with high normal blood pressure. Those eligible had a diastolic pressure of 80-89 mmHg.

A total of 2,182 subjects were enrolled in Phase 1, a short-term study that tested seven interventions, including lowering sodium intake. Phase 2 enrolled 2,382 subjects in a study lasting 3 to 4 years. It tested three interventions: weight loss, sodium reduction, and the combination.

The sodium reduction group marginally reduced blood pressure after three years by 1.2 mm Hg systolic, 0.7 mm diastolic, compared to a control group.

The rationale for reducing high normal blood pressure was challenged by a 2009 Cochrane Review article. The article reported that reducing blood pressure below 140/90 is not beneficial.


“Using more drugs in the lower target groups did achieve modestly lower blood pressures,” the Cochrane study said. “However, this strategy did not prolong survival or reduce stroke, heart attack, heart failure or kidney failure. More trials are needed, but at present there is no evidence to support aiming for a blood pressure target lower than 140/90 mmHg in any hypertensive patient.”