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Salt is bad for your blood pressure. We've known that for a long time, from both associational studies and randomized trials. People and populations with high salt intake have more hypertension and strokes. If you lower patients' salt intake in research trials, their blood pressure goes down. But what about morbidity and mortality? Stands to reason that they would go down too, but until now it hasn't been shown clearly.
Nancy Cook and colleagues followed up patients from two large American hypertension prevention trials of patients with high normal blood pressure (doi: 10.1136/bmj.39147.604896.55). In both trials, the original interventions—weight loss, counseling to decrease dietary sodium, or both—led to decreased blood pressure compared to controls. Now, 10-15 years after the trials concluded, the investigators report cardiac morbidity and mortality data for more than 75% of the patients.
After adjustment for baseline characteristics, a 25% reduction in the risk of cardiovascular disease occurred among those who had received the sodium reduction interventions. Given the fact that the research interventions had ended years previously and the general tendency for behavioral interventions to attenuate over time, this is a remarkable finding. The difference in mortality between the groups did not reach significance.
In a related editorial, Francesco Cappuccio points out that most dietary salt in developed countries comes from eating processed foods and bread (doi: 10.1136/bmj.39175.364954.BE). Thus, messages to “throw away the salt shaker” would have little effect. It seems clear that the only way progress will be made is if manufacturers reduce the sodium in prepared foods, either voluntarily or by regulation.
Almost a year ago, the American Medical Association joined public health groups in calling for at least a 50% reduction in the amount of sodium in prepared foods, fast foods, and restaurant meals; improved labeling of sodium content in foods; and the withdrawal by the FDA of the “generally recognized as safe” status of salt (www.ama-assn.org/ama/pub/category/16461.html). Little has happened. Without some sort of regulatory action we are unlikely to make much progress against this common but now clearly dangerous dietary ingredient.