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Take This Study With Many Grains Of Salt: More Salt Linked To Fewer Cardiac Deaths

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Stop. Step away from the chips and pickles.

True, a European study that just came out in the Journal of the American Medical Association would seem to suggest that eating a lot of salt actually reduces your risk of cardiac death. It would seem to fly in the face of years of warnings that too much salt is bad for us, and the mounting public health efforts in cities like New York and Boston to help people limit their salt.

But Dr. Randall Zusman, director of the section on hypertension and vascular medicine at the Massachusetts General Hospital Heart Center, says the study is absolutely not a “pass” to the pickle jar. Rather, he says, it opens the way to some interesting hypotheses that remain to be explored.

The study followed more than 3,600 subjects for several years, and found the highest number of cardiac deaths in those who consumed the least salt, as tested once in their urine. Those with the highest salt intake had the lowest number of deaths. Higher salt intake also didn’t seem to translate to higher blood pressure over time. The authors conclude that lowering salt intake is helpful for people who already have high blood pressure, but not as a policy for the population at large.

I asked Dr. Zusman to explain.

Dr. Randall Zusman of Massachusetts General Hospital
Dr. Randall Zusman of Massachusetts General Hospital

You read it correctly. That’s the conclusion that they would like to suggest as the result of their findings. The problem is that this was not intended to be an assessment of the benefits of the reduction of salt intake as an intervention for global population health.

They took a bunch of people and they looked at their salt intake, and they found, looking in a very narrow fashion, that the more salt you ate, the lower your risk. It’s completely contrary to everything that we believe. But they also found that rather dramatic changes in salt intake — 100 millimoles which is about two grams of salt — changed blood pressure by about two points, which we know from other studies ought to increase risk. Two points on a population basis is significant, though on an individual basis it’s not.

As the authors point out, not only are their results controversial, but they have a lot of faults or shortcomings. They didn’t take these people and then prospectively attempt to control their salt intake and look at the impact of modifying their salt ingestion. They took one urine sample at one point of time and took a hugely broad brush and made conclusions for the world.

Q: So what should we make of their findings?

The most important thing is that they’re hypothesis-generating. They’re suggesting that perhaps we don’t understand as much as we thought we did about salt, cardiovascular disease and blood pressure. But the other thing, as they point out, is that they had a bunch of white Europeans. Nobody of any other demographic characteristic. They looked at a single point in time. They made, for example, five blood pressure measurements to come out with a mean average number, but they accepted a single urinary measurement as a valid reflection of their population, which I think gives short shrift to the fact that people vary in their diets. If you have a pickle on Friday and they collected a sample on Saturday, you have a very different number than if you worked all day and never ate at all.

The other thing is that they completely ignored many other known cardiac risk factors. We don’t see anything here about cholesterol, about the relation to weight, to exercise, to family history, to electrocardiographic abnormalities, to newer known biomarkers of cardiovascular risk, to the use of statins, to the use of aspirin, all sorts of things. This is a lot of work, and I don’t want to minimize the amount of work, especially by [lead investigator Jan] Stassen, who’s a giant in the field. He’s a very respected, well-recognized investigator. But they themselves point out that their results are not what they expected and that there are shortcomings. That’s why I think this should be hypothesis-generating.

The other thing is that the benefits of salt restriction are not necessarily in the prevention of the development of high blood pressure, they’re in the sensitization, if you will, of patients to the strategies we employ to control their blood pressures. So when I ask my patient to reduce his or her salt intake, it’s not because I necessarily think doing so will in and of itself control the blood pressure, but it will make them more sensitive to the interventions I propose, like the anti-hypertensives we use. Say I gave you a diuretic and you are a saltaholic. You will in part negate some of the potential benefit of the diuretic in preventing sodium retention.

So one of the problems with this study, and I see it getting big play, is people will say, “Aha! I’ve known all along, I don’t need to listen to Dr. Zusman, who is such an ogre and won’t let me have pickles, pretzels, potato chips, or my favorite canned soups or even cheerios or Greek cheese, or fast food or pizza or soy sauce.” And they will go off their low-salt diets. When we’re actually talking about two completely different things: One has to do with prospective effects of salt on the development of events, the other has to do with the known benefits of controlling blood pressure.

The only way to really test this hypothesis is: You take 200 million people, you take all of the known characteristics for cardiovascular disease, and you divide them among three groups, and then you control their salt intake. One group eats pickles and pretzels at will; the second group eats fresh fruits and vegetables; and the middle group eats the traditional diet, and then we see 20 years down the road which ones we killed and which ones we didn’t. And then we project that for the next millennium, and include Asians and African-Americans.

The study homed in on a very important parameter, to the exclusion of all the other known contributory factors. What I’m trying to convey is that I have admiration for what they’ve done but I think its interpretation by the lay public may be dangerous.

Q: So it’s clear we shouldn’t be reaching for the chips, but I do come away wondering whether this study doesn’t raise enough doubt so that maybe public policy shouldn’t be fighting salt so hard among the general population, as in, say, New York City...?

I’m firmly behind Mayor Bloomberg’s effort. The reason I say that is salt restriction, by definition, also comes with a lot of other good restrictions. So the things you shouldn’t be eating if you’re trying to reduce your salt intake — pickles, pretzels, potato chips, olives, anchovies — there’s a fair amount of carbs there. Canned products are processed and depleted of their natural antioxidants and have added preservatives. Luncheon meats — lots of fat. So going on a low salt diet, when I describe it to my patients, involves fresh, fresh, fresh. I tell them you go to the market, come in the door, turn right and go to the fresh fruits and vegetables, load up on brightly colored foods, go to the eggs, go to the juice and milk, maybe make a stop at the fish counter or lean meats, and get yourself out of the store.

Q: So bottom line?

The known risk factors for cardiovascular death and events include: high blood pressure, high cholesterol, diabetes, obesity, a sedentary lifestyle and a family history of cardiovascular disease. Before initiating or radically altering your lifestyle, know these numbers, and discuss them with your physician so that you can fashion an individually designed regimen to reduce your personal risk.
Don’t interpret this study as a pass to dietary indiscretion, whether it be salt, fat, protein, cholesterol or other components.

This program aired on May 3, 2011. The audio for this program is not available.

Carey Goldberg Twitter Editor, CommonHealth
Carey Goldberg is the editor of WBUR's CommonHealth section.

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