To Salt or Not To Salt?Monday, May 20, 2013
Unbeknownst to many readers, the first 10 years of my research career was built largely on studying the effects of salt (or rather sodium chloride) on blood pressure.
In over 40 peer-reviewed publications, we described in excruciating detail the physiological effects of increasing and decreasing sodium intake, in many cases using single-blind randomised trial designs in hundreds of volunteers.
We not only examined the effects of salt on blood pressure but also on a wide range of physiological, metabolic and psychological parameters. We studied the effects on acid-base balance, we conducted genetic studies, we even performed in vitro studies on cells cultured from “salt-sensitive” and “salt-resitant” individuals.
In many respects, these studies left me as confused about the role of sodium on these parameters as I was before. Not that we did not report findings that helped us better understand the complex physiology of sodium homeostasis – it is just that we failed to convincingly demonstrate any major health implications of these findings. In some cases we even reported adverse consequences of sodium restriction resulting both in significant elevations in plasma lipids and insulin resistance (perhaps not surprising given that reducing sodium intake markedly stimulates both the sympathetic and renin-angiotensin systems – the very systems we seek to block to reduce cardiovascular risk).
That was almost 20 years ago – the field does not appear to be much clearer today.
Thus, although surprising to some, I must admit that I was by no means surprised by the report on sodium released last week by the Institute of Medicine, with the rather revealing conclusion that,
“…the evidence from studies on direct health outcomes was insufficient and inconsistent regarding an association between sodium intake below 2,300 mg per day and benefit or risk of CVD outcomes (including stroke and CVD mortality) or all-cause mortality in the general U.S. population.” (or any other population for that matter)
This is not to deny that despite considerable methodological problems (not least in the actual measurement of salt intake), there is evidence to support the idea that higher salt intake may affect blood pressure and possibly cardiovascular risk. However, the data is certainly far less conclusive than food bloggers and health activists would lead us to be believe.
Not surprisingly, the same activists and organisations are now up in arms stopping just short of criticizing the scientific credibility of the IOM expert committee – no doubt, the same folks would have been applauding the conclusions of this “illustrious panel”, had the findings been more in line with their own activist agendas.
What is perhaps even more infuriating to those who have always considered the issue of sodium recommendations a slam-dunk case is the statement by the IOM that, there is in fact no basis on which to draw recommendations for the general public in recognition of the fact that significant proportions of the population may require higher sodium intakes and may even be likely to suffer harm from overly enthusiatic sodium restriction.
While I have no illusions that this report will in any way put the century old debate to rest (indeed the report calls for further research), I think that there is a much bigger message in this report that should let us tread cautiously when it comes to dietary recommendations in general.
Let us remember that associations (on which so many of our assumptions about healthy diets depend) simply do not prove causality, even when backed by seemingly plausible biological hypotheses derived largely from rodent toxicology. We should also remember that fancy statistical predictions on the vast number of lives lost or saved by altering the population intake of this or the other nutrient, are generally based on sometimes rather heroic assumptions that may well explain whey they are rarely (if ever) borne out by actual interventions.
Thus, whether we are talking about salt, fat, carbs, sugar, fibre, gluten, calcium, Vit D, dairy or red-meat, a degree of humility in advocating for policies and other measures to reduce or increase this or the other is generally in order.
Seldom in the field of nutrition are things as cut and dried as some will have us believe – if only food were as simple as tobacco.
New Delhi, India
Disclaimer: I was invited to be on the IOM Expert Committee but had to decline due to other obligations.
Monday, May 20, 2013
I do wish other “experts” would exhibit a similar degree of humility. Back 40 years ago, when there was another anti-salt wave, I cut my own salt intake a lot. One day, I got dizzy and realized that when I ran, my sweat had no salt in it. I started salting my food as I had been wanting to, which was one pass of a half-plugged up shaker over my eggs, and I went back to normal.
I salt my food as I want to. And it isn’t much, but it is needed.
Monday, May 20, 2013
I have often wondered about this low salt trend especially in the elderly. I’ve seen some very significant, symptomatic cases of hyponatremia (even in the absence of diuretic use) in older patients who have seen this info and are not salting their food. The resulting dizzy spells especially in the elderly can cause some nasty falls resulting in fractures, concussions, etc.
Thank you for this information. I am puzzled about how the 1500 mg/day recommendation came about.
Monday, May 20, 2013
“Data” is plural.
Tuesday, May 21, 2013
Would someone please tell Michael Bloomberg
Monday, May 27, 2013
While all this may be so, I’m concerned that the interpretation will be “bring on the chips and other salty snack foods, ultra-processed convenience foods and fast food” which happen to be laden with sodium that are the fastest growing sector of our food supply (and make it very easy to have way more than 2300 mg/day). I can just hear Frito-Lay now saying their products are in fact “functional foods”…