Once again the American Heart Association has taken a strong stance against science. Of course, that’s not how the AHA phrases it. In its own words the AHA says it “strongly refutes the findings” of a “flawed study” which “you shouldn’t use… to inform yourself about how you’re going to eat.”
But in fact the AHA position is really a strong blow against science and the scientific process.
The current case revolves around a study published last Friday in the Lancet which suggested that salt restriction in the diet won’t benefit most people and may actually cause harm, though the study did also suggest that salt restriction might help the 11% of the population who have high blood pressure and consume a lot of salt.
The average American consumes about 3,400 mg per day of sodium. The AHA recommends that sodium levels be cut by more than half to 1,500 mg/day. Several other health organizations also recommend reduced salt intake, though their recommendations are less severe than the AHA’s (which is itself a good indication of the lack of scientific consensus).
First it’s important to admit that the AHA has a legitimate point: the Lancet study is by no means perfect and it certainly doesn’t “prove” the case against salt restriction. The study, I think everyone would agree, has all the usual limitations of an observational study. It can detect an association or link but it is unable to demonstrate cause and effect. The study is further weakened by its reliance on a morning urine collection to calculate sodium excretion and then estimate dietary sodium. The authors claim that this technique has been validated in previous studies, but it is important to acknowledge that this is an imperfect measure at best.
The key point here is that the authors of the Lancet study make no claim that their study is definitive. Instead they point out that the study was performed in the first place in response to earlier, less definitive studies hinting at possible harms associated with severe salt restriction.
The AHA is quick to find limitations in the Lancet study but it doesn’t acknowledge that its own evidence supporting salt restriction is itself profoundly imperfect. In fact, the entire case for salt restriction is based on the observation that salt raises blood pressure and that increases in blood pressure can lead to cardiovascular disease. Now it is absolutely true that high blood pressure can cause cardiovascular disease. This is about as well established a fact as can be found in the messy world of medicine. But it does not necessarily follow that any method to lower blood pressure will have a beneficial effect.
We now know that blood pressure lowering drugs, for instance, should not be chosen solely on the basis of their ability to lower blood pressure. Before gaining approval a new blood pressure drug needs to demonstrate not only that it can lower blood pressure but that it is also safe. The reason for this is that there have been several instances in which blood pressure drugs have failed because they were shown to be unsafe, despite their ability to lower blood pressure. The only way to prove these drugs are safe is through randomized controlled trials.
The main difference between drugs and dietary interventions is that we know much less about nutrition. It’s (relatively) easy to test a drug in a blinded and randomized controlled trial. But when it comes to nutrition it’s almost impossible to perform large, long-term, randomized, well-controlled, and well-designed trials of free-living human beings. The fact is no one really knows for sure the long term effects of large scale interventions involving an essential nutrient like sodium.
A former president of the AHA, Elliott Antman, described the AHA as a “a science-based organization dedicated to saving and improving lives.” “Confusion about something as dangerous as excess sodium is unacceptable. We owe it to the public to provide the most scientifically sound dietary advice.”
But although “confusion” about sodium may be “unacceptable” it may also be inevitable, at least for now. Despite what Antman and the AHA say, there is no widespread scientific consensus about salt. In its statements the AHA never acknowledges the lively ongoing debate about salt.
Just how divided is the field? When the New England Journal of Medicine published an earlier version of the Lancet study it was accompanied by an editorial that also expressed disagreement with the AHA’s low salt recommendations. Unless and until there is better evidence, “the results argue against reduction of dietary sodium as an isolated public health recommendation,” wrote the editorialist, Suzanne Oparil. Now here is a truly amazing fact: as I wrote at the time, Oparil is, herself, a former president of the American Heart Association, as well as the American Society of Hypertension. This doesn’t mean the AHA position is wrong, or that its opponents are right, but it does mean that it is patently absurd to pretend that the scientific question is settled.
It’s also worth noting that the senior author of the Lancet study, for instance, is Salim Yusuf, a top cardiologist who has been one of the most frequently cited scientists in the world. Again, number of citations or eminence in the field should not determine who is right and wrong. But it at least suggests that there is another side to the story that the AHA and Antman want us to ignore.
It’s hard to overstate the potential dangers of getting something like this wrong. As I’ve noted several times in the past, the American Heart Association should be especially careful in this regard, since it’s already been down this road before, with disastrous consequences. Back in the 1980s the AHA developed enormously influential guidelines on cholesterol and diet. These guidelines helped spark the campaign against dietary fat and had the catastrophic consequence of pushing people to consume more carbohydrates, including sugar, instead of fat and protein. We will probably never know the full extent of the damage, but many have speculated that this may have contributed to the obesity and diabetes epidemics. Let’s make sure this doesn’t happen again with salt.
Let me be clear: I see no reason why the AHA shouldn’t make its case for low salt and shouldn’t issue recommendations. But they should first of all admit that this is the opinion of their own experts and that there are many other reputable scientists who disagree. The AHA can’t be judge and jury and simply declare themselves the winner in the court of science.
Science is about the accumulation of knowledge, and there are many things, like the fact that the earth revolves around the sun and not the other way around, that we now know that we didn’t know before. But the health effect of low salt isn’t the same by any means, and science is often about the process of accumulating that knowledge as much as it is about the knowledge itself. The Lancet paper is an excellent example of one small step in that accumulation. It may turn out to be mistaken, but it also may prove correct.
Previous Coverage of the Salt Debate:
- Salt, Science, And The American Heart Association’s Double Standard
- Get Rid of Sugar, Not Salt, Say Authors
- An Expert’s Perspective: Why Salt Is Not Like Tobacco And Why Guidelines Are Tricky
- Salt Report From IOM Sparks Much Heat, Only A Little Light
- Why Guidelines Are Bad For Science
- Why Guidelines Should Be Waged Like War
- New Studies Fuel The Debate Over Sodium