Population-wide cut in salt not beneficial

People with lower sodium excretion – a marker of salt intake – had increased cardiovascular mortality, and those with higher sodium excretion were at no increased risk of hypertension, found a study in this week’s JAMA.

Researchers in Belgium set out to confirm assumptions, based on results from short-term and observational studies, that a population-wide reduction in salt intake would reduce the rate of cardiovascular events –  but their study produced directly contrary results.

They followed 3681 people enrolled in genetics and hypertension studies, for a median of 7.9 years. At baseline none had cardiovascular disease (CVD) and 2096 were normotensive. At last follow up, 1499 participants’ blood pressure and urinary sodium excretion were both recorded.

Cardiovascular mortality during follow up was significantly inversely associated with 24-hour sodium excretion – it was 4.1% in the tertile with the lowest sodium excretion, compared with 0.8% in the tertile with the highest sodium levels. However there was no significant association between either baseline sodium excretion and total mortality; or sodium excretion and total (fatal + nonfatal) CVD events.

The authors found no association between increasing baseline levels of 24-hour urinary sodium excretion and incidence of new hypertension during follow-up. But, they said, “in multivariable-adjusted analyses, a 100mmol increase in sodium excretion was associated with 1.71mmHg increase in systolic blood pressure (P.<001) but no change in diastolic BP”.

The authors conclude: “The associations between systolic pressure and sodium excretion did not translate into less morbidity or improved survival. On the contrary, low sodium excretion predicted higher cardiovascular mortality.

“Taken together, our current findings refute the estimates of computer models of lives saved and health care costs reduced with lower salt intake. They do also not support the current recommendations of a generalised and indiscriminate reduction of salt intake at the population level."

But they were at pains to point out that for individual patients with raised blood pressure, salt reduction remains important. They concluded: “[Our findings] do not negate the blood pressure-lowering effects of a dietary salt reduction in hypertensive patients.”

Neither the study nor authors had any declared links to the food industry.