Take a Pinch of Salt with This Result

Only occasionally do I post about a study that produces a major surprise or a contradictory result.  But here’s one that’s produced quite a lot of controversy; it’s published in the Journal of the American Medical Association.    

Current recommendations support a generalized reduction of salt intake by everyone; this would supposedly reduce the cardiovascular death rate and health care costs, starting with a reduction in people’s blood pressure.  But the JAMA study challenges this idea.  European researchers decided to see whether 24-hour urinary sodium output is associated with blood pressure changes and health outcomes. The 24-hour sodium excretion is considered a direct and reliable reflection of sodium intake.  Participating in the study, which was run in Belgium and 4 other European countries, were 3,681 adults who were free of cardiovascular disease; 57% of them had normal blood pressure initially.  Blood pressure and 24-hour sodium excretion were measured at baseline and at follow-up, and the occurrence of hypertension and mortality were determined during the average 8-year follow-up.

The participants were classified into 3 groups, or tertiles, based on their 24-hour sodium excretion. There were 50 deaths in the low sodium excretion tertile (average 107 mmol/24hr), 24 in the medium tertile (average 168 mmol/24hr), and 10 in the high tertile (average 260 mmol/24hr).  The respective death rates were 4.1%, 1.9%, and 0.8%.  In the 57% of participants who had normal blood pressure at baseline, the risk of developing hypertension was not increased across the increasing tertiles.  In one analysis, however, after corrections were made for possibly interfering factors, a 100mmol increase in sodium excretion was associated with a 1.71 mg Hg increase in systolic, but not in diastolic blood pressure.   

This result was unexpected by many of the international experts who are crying for the World Health Organization to recommend salt restriction as the next thing to be pushed worldwide after tobacco reduction.  At present, an attack on the JAMA study is spearheaded by Dr G Macgregor of London.  He believes it is a badly written report of a study with severe methodological problems, and says it is not worth paying attention to.  “It’s like saying we don’t think cigarettes are harmful so we shouldn’t do anything about smoking”.   So don’t refill the salt cellar just yet, however attractive the results of the European study seem.