• A study notes that in England from 2003 to 2011, there was a significant fall in BP and mortality from stroke and ischemic heart disease which may have been contributed to by a fall in sodium intake.
• Note that in another study looking at trends over time, stroke mortality has decreased in all Economic Cooperation and Development countries (except Poland and the Slovak Republic).

Welcome to Newman’s Notes, a regular column by David H. Newman, MD, the director of clinical research in the department of emergency medicine at Icahn School of Medicine at Mount Sinai. Newman, who also co-founded theNNT and authored “Hippocrates’ Shadow: Secrets From the House of Medicine,” reviews a variety of recently published studies. MedPage Today lightly edits his comments, adding links and additional sources.

This week: He, FJ, et al “Salt reduction in England from 2003 to 2011: its relationship to blood pressure, stroke and ischaemic heart disease mortality” BMJ Open 2014; DOI: 10.1136/bmjopen-2013-004549

The Study

The BMJ published this dietary salt intake study. And it looked at the U.K. when they started a public health initiative that was all about reducing dietary salt intake.

They tracked outcomes like stroke mortality and heart mortality in the years through and after that salt reduction initiative. And they had some really interesting findings on cardiovascular mortality.

The Findings

The authors found that from 2003 to 2011, there was a decrease in mortality from stroke by 42% (p<0.001) and ischemic heart disease by 40% (p<0.001). They also noted that blood pressure fell 3.0±0.33/1.4±0.20 mm Hg (p<0.001/p<0.001). And these drops were tied to their initiative to reduce salt intake, as measured by 24 hour urinary sodium, which decreased by 1.4 g/day (p<0.01) over that time period in a “random sample” of people.

So, that finding turned into an editorial in The New York Times that suggested we ought to do the same. We ought to reduce the grams of dietary salt intake with a similar public health initiative in the U.S.

The editorial basically said, “Hey man, we ought to be doing this, too. We ought to be reducing salt. Dietary salt intake ought to be reduced because in the U.K. over the time period when they actually reduced dietary salt intake, their stroke mortality and their cardiovascular mortality both plummeted.” And wow, what a public health success.

Flawed

Unfortunately, if you go back to the article, the study actually tracks the time period from the early 2000s to about 2009 and 2010 and says, “Hey, stroke mortality, cardiovascular mortality is getting better.”

If you look at the U.K., there are a whole bunch of useful national statistics. That’s because in the U.K. there’s all kinds of nationalized databases and there’s wonderful publications that describe exactly what’s happening and mortality for different diseases in that country.

And there’s easy access – you can just Google it. You can find stroke and cardiovascular mortality in the U.K. for the 20 and 30 years before they did the dietary salt intake intervention.

When you look at the mortality trends, it’s going down and down and down and down and down. And then 2002/2003 hits when they start the dietary salt intake and the trend keeps going down and down and down and down and down — at exactly the same rate. Conveniently, the study authors chose to only include the graph of the trend line starting in 2003.

But look back (here’s Scotland’s lines, and an OECD comparison for example), and it doesn’t change at all. Literally, there is not a blip in the slope of that line.

Silly, Crazy

First, it’s a little bit silly to be talking about how the dietary salt intake had any impact on stroke or heart mortality in those years. The decline had nothing to do with salt shakers — it was going down all along.

Now, you could make the argument that maybe in 2003 all of a sudden stroke mortality and heart mortality would have gone up or would have leveled out if there wasn’t a dietary salt intake reduction.

But if you make that argument, again, it’s awfully wishful. It’s certainly conjectural.

It’s crazy to look at that kind of data and say, “We ought to start a national stroke and heart mortality reduction program that keys and spends money and resources based on dietary salt intake reduction” based on a single study from a slice in time where before and after that slice in time stroke and heart mortality were already going down.