Salt in the Wound: Experts Clash Over Ideal Sodium Targets in Hypertension

ORLANDO, FL—There’s near-universal agreement that too much sodium in the diet is a bad thing, but that’s about where the consensus ends, with numerous organizations and societies taking a different stance on just how low to go with salt in patients with hypertension.

Two experts took on this contentious topic here at the American College of Cardiology (ACC) 2018 Scientific Session, with Robert Eckel, MD (University of Colorado Hospital, Aurora), arguing that the optimal amount of sodium for the management of hypertension is less than 2,300 mg/day. Martin O’Donnell, MD (National University of Ireland, Galway), on the other hand, said he believes that such a target is not only unreachable but destined to disappoint.

“Even if it were practical, it’s unnecessary,” said O’Donnell. “We are setting ourselves up to fail, and more importantly, we are setting our patients up to fail.”

Instead, O’Donnell argued that physicians need to focus on the 20% of the population who still consume high amounts of sodium, such as those exceeding 5,000 mg/day. The goal should be meeting a population-wide target of “moderate” sodium consumption, rather than aiming to get individual patients to adhere to an unrealistic threshold, since this will have the greatest impact on population health.

We are setting ourselves up to fail, and more importantly, we are setting our patients up to fail. Martin O’Donnell

Eckel acknowledged that any lifestyle intervention studied longitudinally is a daunting task given the tendency for people to lapse from the therapy. “But I treat one patient at a time, and all the guidelines say to restrict dietary sodium,” he said. “So I would [argue] that, treating one patient at a time, salt restriction lowers blood pressure.”

What Do the Experts Say?

The World Health Organization currently recommends individuals consume less than 2,000 mg of sodium per day. The American Heart Association (AHA) takes a somewhat stricter line, arguing that an ideal sodium target is 1,500 mg/day, although they do concede a daily maximum allowance of less 2,300 mg/day.  

Eckel, who co-chaired the 2013 ACC/AHA lifestyle guidelines for the reduction of cardiovascular disease, said patients advised to lower blood-pressure levels should adhere to the DASH diet, the AHA diet, or the USDA dietary pattern, and consume no more than 2,300 mg of daily sodium. Reducing sodium to 1,500 mg/day, which can be achieved with the low-sodium DASH diet, is even more desirable given its beneficial effects on blood pressure.

Compared with a daily intake of 3,300 mg/day, the DASH and low-sodium plans would reduce systolic blood pressure by 2 mm Hg and 7 mm Hg, respectively. However, even if individuals are unable to achieve those targets, decreasing sodium intake by at least 1,000 mg per day would also significantly impact blood pressure, said Eckel.  

In his argument for sodium restriction, Eckel cited several studies, including the 1998 TONE study of patients treated with one antihypertensive medication. After 3.2 months, approximately 90% of those who reduced their daily sodium intake to less than 1,800 mg/day were off medical therapy.

I treat one patient at a time, and all the guidelines say to restrict dietary sodium. Robert Eckel

A more recent Cochrane analysis of the effects of a low-sodium diet versus a high-sodium diet, which was defined as approximately 1,500 mg/day versus 4,600 mg/day, showed there was a significant reduction in systolic and diastolic blood pressure in white hypertensive subjects. In black and Asian subjects, there was an even bigger reduction in systolic and diastolic blood pressure, said Eckel.

The 2017 US guidelines for the treatment of hypertension recommend sodium reduction as part of a nonpharmacological treatment strategy for adults with elevated blood pressure or hypertension (class IA). Adults with elevated blood pressure or stage 1 hypertension and a 10-year atherosclerotic CVD risk of less than 10% should be managed with a nonpharmacological approach first and then have their blood pressure assessed again in 3 to 6 months, according to the guidelines. 

Unrealistic Targets

For O’Donnell, though, the current sodium goals, including the higher 2,300 mg/day recommendation, are unrealistic and impractical. Currently, the average intake of sodium in the United States is 3,400 mg/day, according to the Centers for Disease Control and Prevention. Only a minority of the population consumes less than 2,300 mg/day, and almost none of the population consumes less than 1,500 mg/day, said O’Donnell.

“I want to take a step back and ask the questions that sensible patients or clinicians would ask about any targeted modifiable risk factor,” said O’Donnell. “Can it be measured conveniently, reliably, and validly, as is true of most factors? Can it be interpreted by patients and members of the general public? Can low sodium intake of less than 2.3 g per day be achieved, and is there a clinical benefit, most notably beyond blood pressure?”

For him, sodium intake is notoriously tough to measure and the public have no realistic concept of what 1,500 mg, 2,300 mg, or 5,000 mg of sodium per day means in a practical sense. In terms of achieving low daily intakes, including 1,500 mg/day, it can be done, but only if patients are fed as part of a clinical trial, said O’Donnell. Studies that aim to achieve reductions in sodium with dietary counseling are less successful, however.

Most importantly, aside from the effects on blood pressure, there is no evidence showing that lowering sodium levels to less than 2,300 mg/day reduces cardiovascular events. By contrast, there is “reasonable evidence” showing that a reduction from “high” to “moderate” sodium intake does reduce clinical events, he said.

As for what is considered high, O’Donnell said it’s more than 5,000 mg/day and that several clinical trials, including ON-TARGET and PURE, and EPIC-Norfolk, suggest a J-shaped relationship between cardiovascular outcomes and sodium intake. In fact, O’Donnell cited his 2016 analysis of PURE, EpiDREAM, ONTARGET, and TRANSCEND that suggested higher risks of all-cause mortality and cardiovascular events among hypertensive (and normotensive) patients who consumed less than 3,000 mg/day

On average, the lowest risk of cardiovascular disease events is observed among individuals consuming anywhere from 2,700 to 5,000 mg/day of sodium, according to O’Donnell.

A 2017 report from the World Heart Federation, along with the European Society of Hypertension and European Society of Public Health, currently recommends physicians “avoid a numeric target in individual counseling” in low- and middle-income countries given that clinical trials have employed interventions not feasible for population-wide implementation. O’Donnell, who was part of the writing group, said the population-level wide aim is to reduce sodium levels from high to moderate levels.