These questions are of pressing importance for more than merely public health purposes. There are professional reputations and big bucks involved here.
The battle lines are fairly clear.
On one side are the National Heart, Lung, and Blood Institute, the National High Blood Pressure Education Program, and academic experts on hypertension whose careers have been based on funding from these organizations. These parties have long held that it is important to restrict dietary salt as a matter of public policy, for the purpose of reducing the incidence of hypertension in the United States. They cite scores of scientific studies bolstering their argument that high salt intake is responsible for a substantial amount of the hypertension present in our population, and that salt restriction is the best public policy.
On the other side is the Salt Institute, the rich and powerful manufacturers of processed foods (note: virtually all processed foods contain huge amounts of salt), and the academic experts on hypertension whose careers have been based on funding from these sources. These parties site scores of scientific studies bolstering their argument that high salt intake has little to do with the hypertension present in our population, and that salt restriction is bad public policy and possibly dangerous.
Both camps are entrenched, well-armed, and after over 30 years of fighting, battle hardened. There is little chance that something as insubstantial as a new scientific study will change any of their minds.
The bottom-line problem is that salt metabolism, and its effects on hypertension, are extremely complex. And after decades of research, over 20,000 scientific studies have been published on the relationship between salt and hypertension, with conflicting and contradictory results. Since nobody can read all these articles, let alone digest their meaning, hypertension experts are left to pick and choose which articles they think are most important – and invariably, it seems, they pick the articles that seem to bolster their pre-conceived notions. Reading the medical literature on salt has become uncomfortably like reading the Bible: no matter what odd notion you care to espouse, you’ll be able to find something in there to support it. There seems to be little hope that anything approaching an objective resolution of the salt issue will ever be reached – at least among hypertension experts.
Now a new study, published in February 2001 in Hypertension, puts a new spin on the salt controversy that may open a path to “true enlightenment.”
This study, conducted at the Indiana University School of Medicine, suggests that it is not the hypertension produced by salt that is the most important cause of health problems – instead, it’s whether the individual is “salt-sensitive.” For people who are salt-sensitive, the risk of dying from cardiovascular problems are increased with high dietary salt, whether or not they are hypertensive.
People who are salt-sensitive experience an exaggerated blood pressure elevation when they are given a salt load. (There is no standard way to test for salt-sensitivity, and such tests are currently done only in a research setting.) While salt-sensitivity is felt to be a risk factor for developing hypertension, many salt-sensitive people are, in fact, not hypertensive at all. The Indiana study suggests that, while hypertension is a major cause of cardiovascular disease, it’s not the hypertension that causes early death in salt-sensitive people – it’s the salt-sensitivity itself. That is, in these individuals, high dietary salt causes cardiovascular disease even if their blood pressures remain normal.
How does salt cause cardiovascular disease without increasing the blood pressure? Dr. Aviv from the University of Medicine and Dentistry of New Jersey thinks he has the answer – salt increases the reactivity of platelets, the tiny blood elements that help the blood to clot. Thus, he says, high dietary sodium might lead to cardiovascular events like stroke, heart attack, and kidney disease directly, even in the absence of hypertension.
