Extrapolations? Or data?
A recent blog post on salt and health by Carl Hampton "Watch out for the salt!" gets part of the story right:
There have also been discussions between the Salt Institute (didn’t think there was such a thing, did you?) and the Department of Health and Human Services (DHHS). The Salt Institute has pushed for the DHHS to finance a comprehensive study about the health effects of salt. But here is no word as to whether that study will be conducted or not. Funding is really an overall deciding factor.
But Hampton continues: "Many thousands of Americans die each year because of gradual health effects that were caused by high sodium diets."
Just so we all understand what's going on here: in both the U.S. and the U.K. the anti-salt crowd has indicted sodium chloride for hundreds of thousands of deaths annually based on an extrapolation of blood pressure changes plotted against cardiovascular outcomes. Here's the deception: while the blood pressure effect of severe salt restriction is heterogeneous, cutting salt intake in half will, in fact, lower the population's average blood pressure. And it's true, as well, that populations with lower average blood pressure, in fact, have a lower incidence of cardiovascular events. The deception is to assume that lowering blood pressure is the only relevant metabolic effect of reducing dietary salt; it's not. Lowering salt intake stimulates plasma renin activity and sympathetic nervous system activity and worsens insulin resistance. It is the net effect of these changes that should motivate our concern and guide our policy, not the estimates of a statistical model with built-in assumptions that lower blood pressure will cut heart attacks.
What do those studies of the health outcomes of low-salt diets tell us? Short answer: they don't confirm the current policy of cautioning everyone to reduce dietary salt. Read all about it on our website and look at the underlying studies to make sure we have interpretted them correctly (some of the anti-salt researchers were so dismayed not to be able to find a benefit for their favorite course of action that they did not seek to publish their results, though they were presented to their peers in medical society meetings).
Everyone wants to reduce the tragedy of our massive cardiovascular disease risk. Drugs are part of the answer and diet can be too. But what little evidence we have from controlled trials suggests that the better dietary approach would be to improve the quality of our diets with something like the "DASH Diet," high in fruits, vegetables and dairy products -- but silent on the amount of salt.
What we really need, as Mr. Hampton referenced, is a randomized controlled trial of the mortality consequences of low-salt diets -- will they deliver what CSPI and Dr. MacGregor predict or will they confirm the existing observational studies showing no benefit or even a higher risk among those who cut back on salt. The government has already funded the Trials of Hypertension Prevention which examined blood pressure outcomes; substitute hard outcomes like mortality and the design question is solved. It would be costly, but our current policy is trying to mobilize billions of dollars of public health education and food industry technology. We cannot afford to base those very expensive interventions on a theory and an extrapolation. We need a controlled trial of the health outcomes of low-sodium diets.
