A Grain of Salt: Framingham Offspring Data Refute Dietary Sodium Guidelines

The validity of recommendations for restricting dietary sodium has repeatedly been called into question in recent years, with a few studies even suggesting that low levels of sodium may be harmful. In the latest example, researchers found an inverse relationship between blood pressure and sodium, one that translated into lower blood pressure values in those who consumed higher-than-recommended amounts of sodium and potassium.

“The real message here is that we focus too much on sodium and ignore other nutrients that have been known for a good long while to be intimately associated with blood pressure,” said Lynn L. Moore, DSc, MPH (Boston University School of Medicine, Boston, MA). Her study also supports the suggestion that magnesium and calcium are important dietary contributors to the regulation of blood pressure.

The 2015-2020 Dietary Guidelines for Americans recommend limiting sodium intake to 2.3 grams per day, as does the American Heart Association (AHA), which further advises striving for an ideal limit of no more than 1.5 g per day for healthy adults.

Last year, a study published in the Lancet found that consuming less than 3 g of sodium per day was associated with a greater risk of all-cause death or major cardiovascular events compared with more moderate intakes, regardless of whether blood pressure was normal or elevated. The results prompted the AHA to issue a public statement refuting the study and a spokesperson to tell TCTMD that “people’s general health will be improved by eating less sodium.”

In the study presented today at the American Society for Nutrition Scientific Sessions and annual meeting during the Experimental Biology 2017 meeting in Chicago, IL, Moore and colleagues analyzed dietary data from 2,632 healthy men and women aged 30 to 64 years who were part of the Framingham Offspring Study. Daily sodium and potassium intake was classified as low (< 2.5 g and < 2.3 g, respectively) or high (≥ 2.5 g and ≥ 2.3 g, respectively).

Over 16 years, systolic and diastolic blood pressures decreased with increasing sodium intake. Mean systolic and diastolic blood pressures of 129.5 mm Hg and 75.6 mm Hg, respectively, were seen among those in the high-sodium and high-potassium groups compared with 135.4 mm Hg and 79.0 mm Hg, respectively, among people in the low-sodium and low-potassium groups. Individuals who had the highest mean combined intakes of sodium (3,717 mg/day) and potassium (3,211 mg/day) had the lowest overall blood pressures. Calcium and magnesium intakes also inversely correlated with blood pressure in a manner similar to those for sodium and potassium.

Sodium Alone Not the Whole Story

“It’s not really a sodium story, it’s a potassium story,” said Andrew Mente, PhD (Population Health Research Institute/McMaster University, Hamilton, Canada), who commented on the findings for TCTMD. “If you eat an all-around healthy diet with plenty of potassium, that is the best way to lower your blood pressure, rather than focusing on sodium.”

Mente said since potassium generally tracks with minimally processed food like fruits and vegetables, dairy, nuts, and whole grains, the conclusion that can be drawn about the study participants is that despite having higher-than-recommended levels of sodium and potassium, they generally consume a healthy diet.

Echoing Moore, he noted that the study is one more piece of evidence that focusing on a single nutrient to improve or maintain health is not a worthy goal. “We know that the relationship between sodium and blood pressure is a very modest one, and this study reaffirms that,” he observed.

Mente, who was the lead author of the 2016 Lancet study that suggested low sodium may increase cardiovascular events and mortality, said there really is no basis to support the current dietary recommendations.

“We know both from this new study and others that lowering sodium does not necessarily lower your blood pressure, and we have these other recent studies showing unintended consequences or increased harm when sodium is low,” he said. “We also know that currently recommended levels of sodium are related to increased plasma renin and aldosterone levels, as well as increases in lipid levels such as cholesterol and triglycerides. All of that [should] make us pause and reconsider these recommendations, which are based on science from many, many years ago. As new data comes forward, we need to question old dogmas and consider possibly changing the recommendations that we currently have.”

Mente added that “virtually nobody on the planet” consumes sodium in amounts less than 2.3 g or 1.5 g per day, apart from some hunter-gatherer societies. “We’re talking about a tiny fraction of the global population, so what they are currently recommending that people eat is something that nobody eats,” he said.

Moore agreed, suggesting that an appropriate target for dietary sodium for healthy adults is likely to be somewhere between 3 and 4 g/day.

“I think that’s a safe range, because the excess risk of cardiovascular disease and cardiovascular death seems to go up when people hit levels of around 5 g/day,” she said. “That may differ for people who have known high blood pressure and who are salt sensitive. We really need to understand better what the effects of sodium are in that subgroup and possibly make different recommendations for them than for healthy people without high blood pressure.”

While change is never easy, especially in science, Moore said she is hopeful that the next iteration of the dietary guidelines will take into consideration all the sodium data from the last 5 or 6 years.

“The body of evidence is growing, and I think it’s time to really [focus] on identifying appropriate sodium guidelines for individuals with and without existing hypertension,” she concluded.