Associations of urinary sodium excretion with cardiovascular events in individuals with and without hypertension: a pooled analysis of data from four studies
(Side note: sorry, they have a paywall there)
We searched PubMed for relevant research published between Jan 1, 1960, and April 1, 2016, using the term “sodium” or “salt” AND “mortality” OR “cardiovascular” OR “myocardial” OR “stroke” OR “heart failure” OR “sudden cardiac death” in English.
The results showed that cardiovascular disease and death are increased with low sodium intake (compared with moderate intake) irrespective of hypertension status, whereas there is a higher risk of cardiovascular disease and death only in individuals with hypertension consuming more than 6 g of sodium per day
So there you go then, low salt is bad for you and will increase your risk of a heart attack and lowering your salt will only help if you have hypertension and are consuming more than 6g per day.
Oh Wait …
The Lancet quite rightly now faces rather a lot of very vocal criticism for publishing this from some principally because the entire thing is seriously flawed.
Yes, the authors did trawl PubMed and pulled out of other papers that studied all of this, but what they failed to consider was the existing criticism contained within the reviews of those other studies.
- How the salt intake of the participants was measured was seriously flawed. Urine samples were provided in the morning and then the results from that were extrapolated for a 24 hour period, and that in itself is highly dubious because this is simply not an accurate way to actually measure salt excretion.
- You also can’t base salt intake on just this 24 hour period, because the amount of salt you consume will of course vary from day to day, you would need at least a week or two of urine samples to obtain a truly meaningful result.
- Those who participated in the study were seriously ill people, and so those on a very low salt diet were doing so because there were already seriously ill. In other words, it was not the low salt that caused the illness, but rather it was the illness that caused the low salt that they measured.
Professor Francesco Cappuccio, head of the World Health Organization’s Collaborating Centre for Nutrition, attacked both the methods used in the study and the journal for agreeing to publish it.
“It is with disbelief that we should read such bad science published in The Lancet,” he said.
Professor Cappuccio said the article contained “a re-publication of data” used in another paper.
“The flaws that were extensively noted in their previous accounts are maintained and criticisms ignored,”
So back to the question … is salt OK?
What is clear is that the Lancet’s paper does itself have a few rather serious challenges hanging over it for it to be a way of providing a conclusive answer to that.
What is perhaps generally recognised is that when it comes to salt, we have a U curve.
- If you consume way too much salt, then you will probably be risking stroke, high blood-pressure, and cardiovascular disease – (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2782060/)
- Not having enough can also impact you. For example if working in a hot temperature and you rapidly sweat out salt, then your ability to regulate your fluid balance will be compromised
The ideal rests at the bottom of the U curve of not too much and not too little, but as for how much that is … well that as yet remains a contentious topic up for more research and debate. For many (such as Consensus Action on Salt and Health), we already all have way too much, and so it is this orthodoxy that is now being challenged by this dubious study.
As for this specific paper in The Lancet, it is distinctly possible that their conclusion may be correct (or not), but even if you know it might be the right answer, if the methodology utilised to derive the conclusion is dubious and has questions hanging over it, then you simply cannot lean upon it for the modification of public policy.
One Further word on all this
One size does not fit all – salt reduction for the 10% who have hypertension is demonstrably beneficial, but if (and that is a big if) that benefit truly is demonstrated to impact the other 90% in a negative manner, then we really would need to rethink things …
When apparent dogma is challenged, we should speak not of controversy but rather accede to the all-encompassing expression of so-called scientific uncertainty, so as to avoid unbecoming rhetoric. The issue of population strategies for salt consumption is a good case in point. There is no argument other than “excessive salt in the diet raises blood pressure”, and that strategies to reduce salt in individuals with hypertension prevent the cardiovascular consequences of the disease. However, the corollary that reducing sodium intake across populations will be beneficial to all, has been challenged with the assertion that doing so might indeed be harmful.
… we must acknowledge that given the dependency of so many physiological systems on the sodium cation, it should come as no surprise that a low- salt-for-all policy would benefit some and disadvantage others. So rather than allowing contrary evidence to dispel the positive efforts that have been made to reduce the salt content of foods, we must now direct our efforts to formulating a policy that will benefit the majority in society without comprising the minority.
Eoin O’Brien – Molecular Pharmacology, The Conway Institute, University College Dublin,
Bottom Line: We do need to take the claimed conclusion within the Lancet article with a pinch of salt because of the challenges it faces, but we still can’t just dismiss the possibility that current policies just might be impacting 90% of the population in a negative manner.
- a meta-analysis published in The Journal of Hypertension found no strong evidence that reducing salt intake affects the risk of heart attack, stroke or death in people with normal or high blood pressure
- an article published in the Journal of the American Medical Association has reported that those excreting less salt (thus, presumably ingesting less) were at increased risk of dying from heart disease
- a recent meta-analysis conducted by the Cochrane Hypertension group has found that both of these prior articles were subject to methodological flaws, and urges great caution when interpreting their results (Effect of longer-term modest salt reduction on blood pressure. Cochrane Database of Systematic Reviews 2013, Issue 4. Art. No.: CD004937)
We need more robust data if this prevailing thinking is to result in a policy change – simply rehashing that dubious data will simply not cut it.