Killer Foods? Take the News with a Grain of Salt

“Killer foods” stories abound, particularly in the consumer press. While the industry needs to pay close attention to the influences on the buying public, do certain headlines require a panicked response? I asked Dick Hanneman, president of the Salt Institute what he thought of the following headline “Too Much Salt Boosts Blood Pressure,” particularly in light of a piece of commentary more than halfway down the page saying that specific conclusions might be “oversimplification.” Here’s his response:

-Lynn A. Kuntz

The biggest "news" about the HealthDay story “Too Much Salt Boosts Blood Pressure” is: What’s the news?

Everyone has known that salt and blood pressure are linked. The Chinese knew it 4000 years ago. While nobody knows what causes “essential hypertension,” we know that salt is a major factor affecting blood pressure. Studies several decades ago at the University of Indiana clearly showed that about one-third the population would lower blood pressure on significantly lower salt and about one-quarter would increase blood pressure significantly on the same salt reduction. So, that's not news. Overall, scientists are in fairly strong agreement that the blood pressure is heterogeneous (it moves differently in different people and, in this case, in different directions). Scientists also agree that, overall, cutting salt by about two-thirds from our current globally-average intake level of 3,500 mg/day, population blood pressure would fall by 305 mmHg. No news here.

In fact, blood pressure is the wrong outcome to be measuring. Not that it’s not an important indicator. It is. But there are other indicators as well. What elevated blood pressure tells us is that SOMETHING is wrong in the cardiovascular system—a warning to figure out WHAT it is that's wrong. Thus, salt reduction treats the symptom, not the problem.

And the treatment causes problems itself. Low-salt diets cause elevated levels of aldosterone and renin -- both significant risk factors for heart attacks. It induces insulin resistance, impairing the body's ability to metabolize glucose and is a risk factor, itself, for high blood pressure and diabetes. And it stimulates sympathetic nervous system activity. In short, lowering dietary salt triggers changes—in both directions with regard to blood pressure.

Worse, the non-news story on blood pressure further cements the mistaken notion that restricting dietary salt will improve health. Models that assume that the risk profile of populations with natively-lower blood pressure will predict the risk profile of persons who reduce their personal salt intakes (or populations of such individuals) have no foundation in research. They are a house of cards resting on the unproven starting assumptions. You can't model outcomes; you have to show them with data. They haven’t.

When we donate a pint of blood, we reduce our blood pressure. It may improve our mental health, but does nothing for our physical health. We need to look at the health outcomes of the intervention, not the intermediate variables that are the several disparate risk factor changes. In short, the incidence of heart attacks, cardiovascular mortality and all-cause mortality are the proper metric. Only 16 health outcomes studies have been reported. Only one suggests the assumptions of previous models were correct. Fifteen reject that model. Four of them actually find higher rates of mortality and heart attacks on low-salt diets.

Unfortunately, all are observational studies. We need a controlled trial. We asked HHS to fund such a trial many years ago and made a direct appeal two years ago this month. No action. What we get is more of the same. More studies of blood pressure. Why? Because the “official” policy is unlikely to be sustained by a controlled trial of the health outcomes of salt reduction. We have the methodology; the same intervention as we did for the Trials of Hypertension Prevention (Phase II). It should be Trials of Mortality Reduction. We need it badly and we need it now. We have pursued salt reduction and blood pressure reduction for 30 years. No progress through diet (though significant improvement pharmacologically).

Let's have a discussion about health outcomes, not a rehash of non-news about blood pressure.

-Dick Hanneman