Heart Risk due to Too High or Too Low of Salt Intakes

It is well known that too much salt intake increase the risk of high blood pressure and other cardiovascular diseases. However, a new study demonstrates that too low salt intake appears to be associated with an elevated risk of cardiovascular events. This study was published in the November 23/30 issue of the Journal of the American Medical Association.

The relationship between sodium intake and a composite of cardiovascular death, stroke, and heart failure hospitalization was “U” shaped, with elevated risks associated with consumption of more than 8,000 mg and less than 3,000 mg per day, according to Martin O’Donnell, MB, PhD, of McMaster University in Hamilton, Ontario, and colleagues.

“Our findings emphasize the burden of cardiovascular disease associated with excess sodium intake and the importance of population-based programs to reduce sodium intake in populations consuming high-sodium diets,” theese authors wrote.

They noted, however, that risk was not elevated on the upper end of intake until sodium levels exceeded 6,500 mg/day, far higher than the upper limits established by the World Health Organization (2,000 mg/day) and the American Heart Association (1,500 mg/day). That discrepancy is consistent, however, with the conflicting results of observational studies that have examined the association between sodium intake and cardiovascular events.
The researchers argued for the conduct of large, randomized, controlled trials that would evaluate the effect of reduced sodium intake on cardiovascular outcomes among primary and secondary prevention populations, using a multi-factorial dietary intervention.

“Pending the results of such trials, a more cautious approach to policy on sodium intake may be appropriate, one that targets sodium reduction in populations consuming high sodium levels and reflects the uncertainty in those with moderate sodium diets, which includes the majority of the population,” they wrote.

The researchers performed an analysis on 28,880 patients from the ONETARGET and TRANSCEND trials. All were 55 or older and had either established cardiovascular disease or high-risk diabetes. Intake of both sodium and potassium was estimated from baseline urinary samples. Through a median follow-up of 56 months, cardiovascular death, stroke, or hospitalization for congestive heart failure occurred in 16.4% of the patients.

Compared with patients who had an estimated sodium intake of 4,000 to 5,999 mg/day, those who consumed more than 8,000 mg/day had greater risks of the composite outcome and all of the individual components (HRs 1.48 to 1.66). In addition, an intake of 7,000 to 8,000 mg/day was associated with a 53% greater risk of cardiovascular death.

But lower intake also was associated with poor outcomes.
Compared with the reference group, patients consuming less than 3,000 mg/day had elevated risks of the composite outcome and cardiovascular death (HRs 1.16 to 1.37). An intake of 2,000 to 2,999 mg/day was associated with a greater risk of being admitted for congestive heart failure (HR 1.23).

Potassium intake, a proposed modifier of the relationship between sodium intake and cardiovascular disease, was associated with stroke risk only. Compared with an intake of less than 1,500 mg/day, higher consumption was associated with reduced risks of stroke (HRs 0.68 to 0.77).

In an accompanying editorial, Paul Whelton, MB, MD, of the Tulane University School of Public Health and Tropical Medicine in New Orleans, agreed with the researchers that additional clinical trials designed to determine whether sodium reduction reduces cardiovascular events would be ideal, pointing out the limitations of observational studies.

Still, he said, most U.S. adults consume too much sodium and reducing the addition of sodium to foods “could represent one of the ‘lifestyle’ changes with the greatest potential for intervention success.”

“This shift to a more natural diet would concurrently lead to an absolute increase in dietary potassium content and also lead to an improved sodium-potassium ratio, which may be more desirable than change of either electrolyte on its own,” he wrote. “The scientific underpinning for the health benefits from sodium reduction is strong, and the available evidence does not support deviating from the stated goal of reducing the exposure to dietary sodium in the general population.”

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