Created: 25 May 2016
A new study on sodium intake and hypertension has created controversy. The study’s findings, which fly in the face of longstanding guidelines, show that low-sodium diets may not lower—and may even increase—the risk of cardiovascular disease (CVD) and death compared with moderate sodium intake.
Researchers reported that low sodium intake is associated with greater cardiovascular events and death regardless of hypertension. Other experts have strongly disagreed. The only people who need to lower their sodium consumption are those with hypertension who also consume a high-sodium diet, concluded the investigators of the study, which was published online May 29, 2016 in The Lancet. “While our data highlights the importance of reducing high salt intake in people with hypertension, it does not support reducing salt intake to low levels [in everyone],” said the study’s lead author Andrew Mente, PhD, a principal investigator of the Population Health Research Institute (PHRI) of McMaster University, in Hamilton, Ontario, Canada. “These are extremely important findings for those who are suffering from high blood pressure.” But the American Heart Association (AHA) and other groups flatly refuted the study and warned the public not to accept its results. “The findings in this study are not valid, and you shouldn’t use it to inform yourself about how you’re going to eat,” stated AHA President Mark A. Creager, MD, Director of the Heart and Vascular Center at Dartmouth-Hitchcock Medical Center, in Lebanon, NH. “The large body of science clearly shows how excessive amounts of sodium in the American diet can cause high blood pressure, which can lead to heart disease, stroke, and even death.” For this study, Dr. Mente and colleagues in Canada, South America, China, the Middle East, and Europe reviewed data on 133,118 patients (63,559 with hypertension and 69,559 without; average age 55) from 4 large prospective studies. The researchers estimated subjects’ 24-hour urinary sodium excretion as a measure of sodium intake, and related this to blood pressure, cardiovascular events, and death over a 4-year period. The researchers found that high sodium intake (7g/day or more), when compared with moderate sodium intake (3 g to 6 g/day), was associated with an increased risk of cardiovascular events and death—but only in people with hypertension, not in those without hypertension. But they also found that low sodium intake, compared to average intake, was associated with more cardiovascular events and mortality regardless of whether subjects had hypertension. “Low sodium intake [compared to average intake] reduces blood pressure modestly,” Dr. Mente said. “But low sodium intake also has other effects, including adverse elevations of certain hormones which may outweigh any benefits. The key question is not whether blood pressure is lower with very low salt intake, instead it is whether it improves health.” “This study adds to our understanding of the relationship between salt intake and health, and questions the appropriateness of current guidelines that recommend low sodium intake in the entire population,” said study co-author Martin O’Donnell, PhD, Associate Clinical Professor of Internal Medicine at McMaster University and National University of Ireland in Galway. However, a statement from the AHA insisted that the link between excessive sodium intake and hypertension—as well as higher risks of heart disease, stroke, heart failure, and kidney disease—is indisputable. The AHA’s statement also characterized the study as “flawed.” “Low sodium excretion, based on spot urine collections as done in this study, is a misleading measure of usual dietary intake, particularly over a lifetime,” stated the AHA’s Dr. Creager. “Other factors, beyond dietary sodium intake, are present and probably are responsible for the association of lower sodium excretion with cardiovascular disease—factors such as poor appetite and reduced food intake due to a serious concurrent illness.”