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Pass the salt

Salt may have been unfairly targeted as a killer in the healthy heart stakes, according to newly published research.

The observational study of over 90000 people in 300 communities across 18 countries, found that sodium consumption was not associated with an increase in health risks unless the average daily consumption was excessive – more than 5g/day or 2.5 teaspoons of salt. And, this average high daily sodium intake was mostly seen in China, with only about 15% of communities outside of China exceeding this 5g a day limit.

As part of this ongoing Prospective Urban Rural Epidemiology (PURE) study, participants aged 35-70 were assessed initially at baseline and then followed for an average of 8.1 years, over which time the occurrence of any major cardiovascular events or death was recorded.

What the researchers found was that the risk of hypertension and strokes was only increased in communities where the average daily sodium intake was greater than 5g. Perhaps unexpectedly, this higher sodium intake was actually found to be also associated with lower rates of myocardial infarction and total mortality. Furthermore, the research found that very low levels of sodium intake were harmful, being associated with an increased risk of cardiovascular disease and mortality.

The findings fly in the face of the current WHO guidelines that recommend, as a global approach we should be aiming for populations to reduce their sodium intake to below 2g/day.

However, no communities in the study came close to achieving this target. In fact, no communities in the study had an average sodium intake of less than 3g/day, based on morning fasting urine samples from the participants.

“Sodium intake was associated with cardiovascular disease and strokes only in communities where mean intake was greater than 5g/day. A strategy of sodium reduction in these communities and countries but not in others might be appropriate,” the Canadian study authors said.

But before we all go and stock up on our Saxa, an accompanying editorial sounds a word of caution. While acknowledging the findings that ‘normal’ salt intake appeared to be at least health-neutral if not beneficial, the editorial authors remind us that the study is observational and has not taken into consideration a number of potential confounders such as diet. Without taking these confounders into account, one can’t assume that just decreasing salt intake in people at high risk of stroke or increasing it in people at risk of a heart attack will work, they said.

“Nevertheless the findings are exceedingly interesting and should be tested in a randomised controlled trial,” they concluded, adding that such a trial, to be conducted in a US federal prison population had been proposed.




Vol 392 No 10146 pp:496-506

Vol 392 No 10146 pp: 456-458