Too Salt or Not Too Salt?Wednesday, September 29, 2010
Today at 23rd Scientific Meeting of the International Society of Hypertension, I attended a session dedicated to sodium and its impact on hypertension.
As some readers may know, I started my research career back in the mid-eighties studying the phenomenon of “salt sensitivity”, trying to answer the question why some people appear more “sensitive” to the blood pressure effect of salt, while others appear resistant.
This interest has taken me on a long voyage of research that included studying vascular reactivity, the sympathetic nervous system, the renin-angiotensin system, insulin resistance, genetics. and adipose tissue biology.
It turns out that the obesity epidemic has created a population that is increasingly salt sensitive, as hypertension associated with excess weight is largely driven by sodium retention and volume expansion.
There is certainly no doubt, that dietary sodium restriction results in blood pressure reduction, and, as outlined in a talk by Graham MacGregor (UK), there are ample examples of population-wide “interventions” that resulted in lower salt intake and lower blood pressure levels.
The challenge of course is how to reduce salt at a population level, when most of the food in our diet comes from processed foods. Simply banning the salt shaker from the table, has a relatively minor impact on overall salt intake.
As pointed out by Darwin Labarthe (USA), various organisations have called for mandatory restriction of salt in foods. He called on the food industry to voluntarily reduce sodium levels – something that has a precedent in countries like the UK, where many large manufacturers have stealthily reduced salt content of processed foods.
In fact, there are now several companies (perhaps most natabely Campbell’s), which have considerably reduced the amount of salt in their products over the last decade and have set even lower targets for themselves.
Initiatives like the Natioanal Salt Reduction Initiative in New York City, has the goal to reduce salt use in commonly eaten products by 20% in the next five years. There is also evidence that physicians are consistently recommending sodium reduction and that a growing number of consumers do in fact opt for low-salt foods.
In the afternoon, I attended a debate between Graham MacGregor and Simon Rabkin (Canada) on whether or not we have enough evidence to support government restrictions on salt use – Rabkin elegantly argues that, if we apply the standards of “evidence-based medicine” we must acknowledge that there is not a single randomised controlled trial that has ever documented the benefit of lowering blood pressure with salt restriction in “hard” endpoints.
While my own research has moved on and I believe that obesity is probably a far more pressing issue than the amount of salt we eat, I do think that limiting salt intake can help reduce population and individual blood pressure levels. Whether or not, population-wide efforts to limit salt intake will really translate into fewer heart attacks and stroke remains to be seen.