Challenging the Consensus
on Dietary Salt

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How much salt should you be eating? For an estimated 99 percent of Americans, the advice from public-health experts in recent years has been: less—a lot less. Organizations like the American Heart Association recommend a maximum daily sodium intake of 1,500 milligrams. But a May report by the Institute of Medicine, the health arm of the National Academy of Sciences, called that counsel into question, suggesting that there’s no clear reason for most people to shoot for less than 2,300 milligrams of sodium per day—and reducing intake to 1,500 milligrams might even be doing more harm than good.

Brian Strom, the George S. Pepper Professor of Public Health and Preventive Medicine in Biostatistics and Epidemiology, chaired the committee behind the report—whose controversial conclusion made the front page of The New York Times. Strom explained the committee’s rationale to Gazette associate editor Trey Popp.

For years now, American adults have been recommended to limit their sodium intake to about 1,500 milligrams a day. Where did that number come from?

It’s ironic. It came from an Institute of Medicine report in 2005 on recommended daily allowances for lots of different food components, not just sodium. But when it came to sodium, they were unable to come up with a recommended daily allowance. So they came up with a range, where 1,500 milligrams was the minimum amount—not target—that you could eat and still have a well-balanced diet in other ways. And 2,300 was the maximum amount, based on data on blood pressure.
Why does blood pressure matter?

Blood pressure is a biomarker. It doesn’t matter by itself—but it is related to all sorts of other bad things: heart attack, strokes, kidney disease, eye disease, and so on. What really matters is those direct outcomes. But in 2005, when these first recommendations were created, there weren’t data on the actual outcomes.
So how did 1,500 milligrams go from a minimum suggested amount to a maximum?

Government agencies took that Institute of Medicine report and put it in stone, saying that 1,500 to 2,300 was what should be the target—and then went one step further, and said for people who are “high-risk,” they should be lowered to 1,500 milligrams. And that group includes African Americans, people with diabetes, pre-hypertension, hypertension, and anyone over age 51—a majority of the population. The American Heart Association several years later turned around and said, ‘Given that this is most of the population, let’s make it the target for everybody.’
Why would they do that?

It’s a question of faith: lower is better. There was no data—and is still no data— supporting that. In the last decade, there have been a number of ‘true-outcome studies’ that started coming out. There were 38 of them that we found—25 specifically related to cardiovascular disease. And there wasn’t a single study—not one—that showed a benefit as you went below 2,300 milligrams. And there were some studies suggesting possible harm.
What kind of harm, and what might be causing it?

We were focusing on people with heart attacks, strokes, cardiovascular death, and total death. And what you see is, as you go from too much salt to a moderate amount, the risk of those things decrease.

Interestingly, when you statistically control for blood pressure, that benefit continues. So blood pressure is not the whole story here. There’s other stuff happening too. There are all sorts of other things that affect outcomes.

For example, potassium intake. There are suggestions in data—this is certainly not conclusive, but there are suggestions—that potassium may be more important that sodium. Potassium being preventive. So as you lower your sodium, if in the process you are lowering your potassium, you may be doing more harm than good. And if you lower the total amount you eat, you’re going to end up lowering both of them. It’s complicated.
The average American actually consumes something like 3,400 mg of sodium a day. Is that too much?

Probably, yes.
Since salt tends to be present at high levels in junk food, oftentimes those things get conflated. From a public health standpoint, do you think we should really be focusing on salt in and of itself, or would it be better to direct our attention to other things?

Yes and yes—I choose both! Salt is in junk food. But actually, the number one source of salt is bread. Not because it’s so salty, but because we eat a lot of it. In the real world, you can’t remove effects of sodium from the effects of the rest of your diet. Which is possibly why you see these suggestions of harm when you go down too low, because you’re also reducing your consumption of other things that may be beneficial.
How much sodium do you eat?

I have no idea. I have not measured it. Most people don’t know. Most of the sodium we ingest comes in processed foods—in meat, in bread, in the normal foods you are eating. So there’s in fact not much that the normal consumer can do about it, other than look for foods that are lower in sodium. Clearly what would be helpful in general is if food manufacturers gave us products that were lower in sodium, so that people would have a choice.

©2013 The Pennsylvania Gazette
Last modified 07/01/13