Study associates low sodium intake with mortality
by Jeff Gelski
WASHINGTON — Lower sodium excretion was associated with higher cardiovascular disease mortality in a study of 3,681 white Europeans appearing on-line May 4 in The Journal of the American Medical Association.
The Salt Institute, citing the study, called on government agencies to stop their sodium reduction agendas and said the recommendations on sodium in the Dietary Guidelines for Americans should be amended.
“We now know conclusively that the U.S. government’s war on salt consumption will cause harm,” said Lori Roman, president of the Salt Institute, in reference to the study.
Peter Briss, a medical director at the Centers for Disease Control and Prevention in Atlanta, said the study will not alter the C.D.C.’s view on sodium intake.
“Essentially our view is that this single report doesn’t change the large body of evidence that demonstrates lower sodium intake is associated with lower blood pressure and better cardiovascular health,” Dr. Briss said. “There are reasons why this individual study doesn’t trump the rest of the body of evidence.”
He said the European study focused mostly on relatively young people in their 40s while most cardiovascular events happen to people older than that. He also said the small number of cardiovascular events in the study made it hard to draw conclusions.
The European study examined the Flemish Study on Environment, Genes and Health Outcomes and the European Project on Genes in Hypertension. The Flemish study started in 1985 in northern Belgium. People in the study were divided into six subgroups: women ages 20-39, 40-59 and 60 or over, and men ages 20-39, 40-59 and 60 or over. The European Project on Genes in Hypertension began in 1999 and followed a similar protocol.
People were followed for a median 7.9 years. Both the Flemish study and the European project ended in 2008.
After obtaining results, researchers divided people into three groups, or tertiles. The mean 24-hour urinary sodium excretion for each tertile was defined as 106 mmol for the low tertile, 165 mmol for the medium tertile and 250 mmol for the high tertile.
In total, 219 study participants died, which included 84 cardiovascular-related deaths. The risk of cardiovascular mortality was elevated significantly in the low tertile, or lower third, of urinary sodium excretion with a significant inverse association between cardiovascular mortality and tertile of sodium excretion.
“It is unlikely that these findings were due to reverse causality because we excluded patients with a history of CVD (cardiovascular disease),” the researchers said.
People in the study also did not receive any recommendations from the research team about moderating their salt consumption.
“The underlying mechanisms explaining the inverse association between cardiovascular mortality and 24-hour urinary sodium excretion might be that a salt intake low enough to decrease blood pressure also increases sympathetic nerve activity, decreases insulin sensitivity, activates the rennin-angiotensin system and stimulates aldosterone secretion,” the researcher said.
The researchers listed four potential limitations in their study. First, one 24-hour urine collection might be insufficient to characterize an individual’s habitual salt intake, but it does reflect the average salt consumption of groups of people. Second, the study population was relatively young and the number of health incidents, including deaths, was small. Third, since the study included only white Europeans, it did not take into account that Asians or blacks might be more sensitive to salt than white people. Fourth, the study did not assess sodium sensitivity.
The study included researchers from the University of Leuven in Belgium, Jagiellonian University Medical College in Krakow, Poland, the University of Padova in Italy, Charles University in Pilsen, Czech Republic, the Institute of Internal Medicine in the Russian Federation, and Maastricht University in The Netherlands.
The Dietary Guidelines recommends reducing daily sodium intake to less than 2,300 mg and a further reduction of less than 1,500 mg should be sought by people who are 51 and over and those of any age who are African American or have hypertension, diabetes or chronic kidney disease. The Dietary Guidelines says on average the higher a person’s sodium intake, the higher that person’s blood pressure and that keeping blood pressure in a normal range reduces a person’s risk of cardiovascular disease, congestive heart failure and kidney disease.