We've talked about salt before here on Healthcare Triage, with the conclusion that while consuming too much of it's a bad thing, so might be consuming too little.  A new study is making news all over the world that adds to this discussion and in the interest of being (?~0:14) and I hope you watched that episode, we should update our priors based on its results.  That's the topic of this week's Healthcare Triage.

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This new study was a meta-analysis that examined how salt intake is associated with cardiovascular events and death, but it added to the discussion by including hypertension status.  In other words, it wanted to see how salt intake affected those outcomes for people with both high blood pressure and normal blood pressure.  

This is important, because as we've discussed many times here, we've gone in the medical community from recommending that people with high blood pressure massively restrict salt in their diets, to claiming that all Americans are eating too much and need to get to very low levels.

Researchers took data from four large studies that collectively compared more than 133,000 people from 49 countries followed for a median of more than 4 years.  They were about evenly split between people with and without hypertension.  They found that people with high blood pressure seemed to have more of a sensitivity to sodium.  Those with hypertension had an increase of 2.1 millimeters of mercury in blood pressure for each additional gram of sodium versus only 1.2 millimeters of mercury in people without hypertension.

They also found that people with high blood pressure who consumed more than 7 grams of sodium a day had significantly greater rates of cardiac events and death than those who consumed 4-5 grams of sodium per day, hazard ratio of 1.23.  But for people with normal blood pressure, consuming more than 7g a day had no increased risk compared to those who consumed 4-5g per day.  In other words, consuming too much salt appears to be a risk factor for bad outcomes for people with hypertension, but that same concern isn't seen in people with normal blood pressure.

There's more.  People with hypertension who consumed less than 3g of sodium per day also had a higher risk for bad outcomes than those who consumed 4-5g, with a hazard ratio of 1.34.  They had even worse outcomes than the people who consumed more than 7g.  An increased risk was also seen in those who have normal blood pressure who consumed less than 3g per day with a hazard ratio of 1.26.

These results held even when the researchers excluded those with known previous cardiovascular disease, so it seems unlikely that these results are because unhealthy people were the ones consuming the lowest sodium.  There seems to be a pretty good amount of evidence that reducing salt intake in people with high blood pressure who consume an excessive amount is a good idea.  That's where we started back in the day and that concept holds up, but that evidence doesn't support the idea that increased salt content in people with normal blood pressure makes that much of a difference.

Moreover, there seems to be a growing body of evidence that the push for very low levels may be doing more harm than good.  I first discussed this on Healthcare Triage almost two years ago.  Even as new evidence comes to light, the FDA still recommends we consume less than 2.3g of sodium per day.  The World Health Organization still says it should be less than 2.0g, and the American Heart Association still says it should be less than 1.5g for many people.  

More than 95% of the world's studied population consumes more than 3g of sodium per day.  Achieving these very low goals won't be easy.  Large, randomized controlled trials are needed to assess the value of a very low sodium diet.  Usually such perspective trials are meant to confirm the associations we see in epidemiological analyses.  In this case, however, the epidemiological studies point to a harm, not a benefit.

It should be noted that the American Heart Association strongly rebuts these findings, disagrees with them, and has come out pretty strongly against them in a recent press release.  It appears that people with hypertension who are consuming more than 7g of salt a day should reduce their intake.  That recommendation stands.  

Too often in medicine we take recommendations that apply to a select group of high risk people and then apply them too broadly.  That may do no good.  Taking that reduction too far, though, may even backfire.

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