Will lowering salt intake extend your life?

Americans have been told to slash their salt intake by about half, but whether that will actually protect our hearts and extend our lifespans remains a matter of fierce debate among experts. The latest finding, a Cochrane review analysis of seven studies involving 6,250 participants, indicates that reducing sodium in the diet does lead to lower blood pressure but that there’s no proof this translates into fewer heart attacks or deaths from heart disease.

One study of heart failure patients found that those who were randomly assigned to lower their sodium intake to 1,840 milligrams per day experienced more deaths and hospitalizations than those who told to aim for no more than 2,760 mg per day.

But the researchers, who published the finding in the American Journal of Hypertension, emphasize that the reason heart benefits have not been demonstrated may be the design of the studies rather than faulty thinking about the merits of salt reduction. For example, the studies -- each involving anywhere from 42 to 1,213 volunteers -- may have been too small to measure a statistically significant difference in strokes, heart attacks, or deaths in those who lowered their sodium intake compared with those who didn’t. Or perhaps the studies didn’t last long enough to see real benefits.

“We did see a trend towards a reduction in mortality in the shorter term, two to three years,” points out study author Rod Taylor, a professor of health services research at the Peninsula Medical School University of Exeter in an e-mail, though that trend may have been due to chance. Still, Taylor says that the lack of longer-term follow-up data may reflect how tough it is to truly reduce sodium for a decade or more.

The 2010 Dietary Recommendations for Americans say those with heart failure, high blood pressure, and kidney problems -- as well as anyone over 51 and all African Americans -- should get no more than 1,500 mg per day and that the rest of us should aim for no more than 2,300 mg. Yet in most of the studies in the Cochrane review, those with high blood pressure or heart failure aimed to get no more than 1,800 milligrams a day, which is above the lower recommendation.

Thus, results may have been more striking if researchers had been able to lower sodium intakes to currently recommended levels. What’s clear, at least to Taylor, is that greater efforts still need to be implemented to get Americans to eat less salt -- beyond simply advising folks to put down the salt shaker or eat low-sodium packaged goods.

“We need to continue to encourage the food industry to reduce hidden salt,” he says, and to make “better use of food labelling.
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But he’d also like to see better designed and larger studies to see whether these strategies really work, not just to reduce blood pressure but all the life-threatening complications that come with it.