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Salt Study Discounts Link to Hypertension
  MedPage Today
Published: May 03, 2011
In a study that seems likely to re-energize the debate over dietary salt, European researchers found that the changes in the amount of sodium excreted in the urine were related to changes in systolic blood pressure.
But they were not linked to diastolic pressure or the risk of developing hypertension, according to Jan Staessen, MD, PhD, of the University of Leuven in Leuven, Belgium, and colleagues.
And levels of urinary sodium excretion were inversely related to the risk of dying of cardiovascular causes, Staessen and colleagues reported in the May 4 issue of the Journal of the American Medical Association.
Action Points
* Explain that a study of 24-hour urinary sodium excretion found an association between lower excretion and increase in cardiovascular deaths.
* Point out, however, that diagnosis of hypertension did not correlate with lower sodium excretion even though systolic blood pressure was higher.
Taken together, Staessen and colleagues argued, the findings do not support "the current recommendations of a generalized and indiscriminate reduction of salt intake at the population level."
But the findings should be taken with a grain of salt, according to Ralph Sacco, MD, president of the American Heart Association and chairman of neurology at the University of Miami.
The study raises some questions, he said, but the "bulk of the evidence" still supports the view that cutting sodium will reduce blood pressure and improve cardiovascular outcomes.
The heart association earlier this year said the daily intake of sodium should be no more than 1,500 milligrams and Sacco told MedPage Today the group will stand by that.
"One study is not enough to change policy," he said.
The findings come from analysis of participants in two European cohorts, with baseline and outcome data on a total of 3,681 people - the so-called "outcome cohort" - over a median follow-up of 7.9 years, the researchers reported.
Of those, 2,856 agreed to take part in follow-up analyses and were considered as two over-lapping groups.
On one hand, the researchers studied the links between changes in 24-hour urinary sodium excretion and changes in blood pressure, over a median of 6.1 years of follow-up, in 1,429 follow-up participants who had complete and accurate urine collection, no cardiovascular disease, and were not on antihypertensive medication.
On the other hand, they studied the incidence of hypertension over a median of 6.5 years in the 2,096 participants who did not have the condition at baseline.
The cohort was divided into thirds, based on 24-hour urinary sodium excretion, with average levels of 107 millimoles in the low tertile, 168 in the medium group, and 260 in the high tertile.
The study population was relatively young at baseline, the researchers noted, with an average age of 40.9 in the low tertile, 38.6 in the medium tertile, and 38.6 in the high group.
Staessen and colleagues found:
* Cardiovascular deaths decreased across increasing tertiles of 24-hour urinary sodium excretion. There were 50 deaths in the low group, 24 in the medium tertile, and 10 in the high group - 4.1%, 1.9%, and 0.8% of the cohort, respectively - and the differences were significant at P<0.001.
* The risk of cardiovascular death was significantly elevated in the low tertile, with a hazard ratio of 1.56 and a 95% confidence interval from 1.02 to 2.36, which was significant at P=0.04.
* 24-hour urinary sodium excretion was not associated with incidence of hypertension. There were 187 new cases of hypertension in the low tertile, 190 in the medium, and 175 in the high group over the follow-up period.
* In multivariate analyses, a 100-millimole increase in sodium excretion was associated with a systolic blood pressure of 1.71 millimeters of mercury (significant at P<0.001) but no change in diastolic pressure.
The researchers cautioned that the number of events was relatively small, owing to the youth of the cohort. And, they added, it may not apply to people other than those of European descent.
They also did not measure sodium sensitivity, they reported.
The heart association's Sacco told MedPage Today that the study had a young population, with a relatively short follow-up, so that some outcomes - such as cardiovascular death - would be expected to be rare.
As well, he said, findings from an all-white European cohort may not completely apply to the U.S. population, with its large proportion of African Americans and Asians.
Sacco said that the average daily intake of sodium in the U.S. is about 3,500 milligrams, much of it from processed and packaged foods.
"That's a lot of salt," he said.
The Heart Association would like to see that down to 1,500 a day by 2020, he said.
The researchers had support from the European Union, InGenious HyperCare, HEALTH-F4-2007-201550 HyperGenes, the Fonds voor Wetenschappelijk Onderzoek Vlaanderen, the Katholieke Universiteit Leuven, the Polish Ministry for Science and Higher Education, and the Czech Society of Hypertension.
The authors said they had no conflicts.
Primary source: Journal of the American Medical Association Source reference:
Stolarz-Skrzypek K, et al "Fatal and nonfatal outcomes, incidence of hypertension, and blood pressure changes in relation to urinary sodium excretion" JAMA 2011; 305(17): 1777-1785.
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