Another A-Salt on Science

If you wanted a clear example of how desperately some scientists (and I’m using the term loosely) will cling to a beloved theory, you couldn’t do much better this:

A recent meta-analysis of salt-restriction studies that was published in both The Cochrane Review and the American Journal of Hypertension found that cutting back on salt is pretty much worthless.  So naturally, the anti-salt hysterics had to jump in and torture the data to find some meaningless associations and try to save their reputations and careers.

You can read an abstract of the meta-analysis here, but for a plain-English version, I’d suggest reading an article published in the online version of Scientific American titled It’s Time to End the War on Salt.  Here are some quotes:

This week a meta-analysis of seven studies involving a total of 6,250 subjects in the American Journal of Hypertension found no strong evidence that cutting salt intake reduces the risk for heart attacks, strokes or death in people with normal or high blood pressure. In May European researchers publishing in the Journal of the American Medical Association reported that the less sodium that study subjects excreted in their urine—an excellent measure of prior consumption—the greater their risk was of dying from heart disease. These findings call into question the common wisdom that excess salt is bad for you, but the evidence linking salt to heart disease has always been tenuous.

I’d say labeling the evidence linking salt to heart disease as tenuous is being generous.  Non-existent would be the more accurate term, unless you engage in some major cherry-picking.  In real science, no consistency means no validity, and the associations between salt and heart disease or mortality aren’t even close to being consistent.  If anything, the associations are all over the place.

So what ignited the fear of salt in the first place?

Worries escalated in the 1970s when Brookhaven National Laboratory’s Lewis Dahl claimed that he had  “unequivocal” evidence that salt causes hypertension: he induced high blood pressure in rats by feeding them the human equivalent of 500 grams of sodium a day. (Today the average American consumes 3.4 grams of sodium, or 8.5 grams of salt, a day.)

Let’s see … some goofy scientist feeds rats the equivalent of 147 times as much salt as the average human consumes in a day, and the rats developed high blood pressure.  Well, my goodness, let’s toss those salt shakers right now!

Last time I checked, most health authorities were still recommending we consume eight glasses of water per day.  I wonder if it ever occurred to Dr. Dahl to force-feed rats the equivalent of 1,176 glasses of water per day and see how that affected their health.  If he ran that experiment, I’m pretty sure he’d end up declaring water a health hazard.  What kind of hopeless idiots could possibly be swayed by such a nonsense study?

In 1977 the U.S. Senate’s Select Committee on Nutrition and Human Needs released a report recommending that Americans cut their salt intake by 50 to 85 percent, based largely on Dahl’s work.

Ah yes, those idiots.  The same idiots who helped kick off the anti-fat hysteria by seeking “consensus” instead of truth.  George McGovern strikes again.

Scientific tools have become much more precise since then, but the correlation between salt intake and poor health has remained tenuous. Intersalt, a large study published in 1988, compared sodium intake with blood pressure in subjects from 52 international research centers and found no relationship between sodium intake and the prevalence of hypertension. In fact, the population that ate the most salt, about 14 grams a day, had a lower median blood pressure than the population that ate the least, about 7.2 grams a day.

Well, that’s just an observational study, so perhaps we’re not accounting for some confounding variables.  Surely if we restricted salt in a controlled clinical setting, we’d see some real health benefits, eh?

In 2004 the Cochrane Collaboration, an international, independent, not-for-profit health care research organization funded in part by the U.S. Department of Health and Human Services, published a review of 11 salt-reduction trials. Over the long-term, low-salt diets, compared to normal diets, decreased systolic blood pressure (the top number in the blood pressure ratio) in healthy people by 1.1 millimeters of mercury (mmHg) and diastolic blood pressure (the bottom number) by 0.6 mmHg. That is like going from 120/80 to 119/79.

You may recall that some troll who claimed to hold a PhD in science once insisted in several comments that salt is indeed bad for us, and to prove his point he sent me a link to a clinical study in which researchers produced a “significant” reduction blood pressure by drastically restricting salt.  As I explained in my Science For Smart People speech, “significant” simply means that statistically, the results weren’t likely to due to chance.  The “significant” reduction in blood pressure reported in the study that the troll sent me amounted to around three points. In other words, meaningless … all the salt-restricted dieters got out of the deal was some really bland food.

Studies that have explored the direct relationship between salt and heart disease have not fared much better. Among them, a 2006 American Journal of Medicine study compared the reported daily sodium intakes of 78 million Americans to their risk of dying from heart disease over the course of 14 years. It found that the more sodium people ate, the less likely they were to die from heart disease.

And yet various government agencies around the world are telling people to restrict salt … to prevent heart disease, of course.

For every study that suggests that salt is unhealthy, another does not.

Bingo.  No consistency, no scientific validity.  Given an honest analysis of the science, we’d have to conclude that restricting salt is pointless from a public-health standpoint, except as advice given to the few people who are hyper-sensitive to salt.

Now … let’s suppose you’re the chairman of Consensus Action on Salt and Health – kind of a British version of CSPI, only focused specifically on attacking salt in the food supply.  Now let’s further suppose stamping out salt in Britain isn’t a mission quite large enough for your ego, so you’re also the chairman of World Action on Salt and Health.  (In my opinion, if you belong to more than one organization with Action on in its name, you’re probably a menace.)  Finally, let’s suppose both of the organizations you chair depend on donations from people you’ve managed to scare witless about the terrors of salt.

Are you going let a pesky little thing like scientific evidence change your mind?  Of course not.  You’re going to get ahold of that data and (as Dr. Mike Eades would say) torture it until it says what you want to hear.  Which is exactly what Dr. Graham McGregor (who I like to refer to as Action-Action Jackson since he’s the chair of two Action organizations) did after the Cochrane Collaboration issued its report.

In a response published in the Lancet, Dr. MacGregor and Dr. Feng He revealed how they concocted a brilliant method of getting around inconvenient facts like these:

As previously reported by heartwire, Taylor et al’s meta-analysis included seven randomized controlled trials of dietary salt reduction in normotensives (three studies), hypertensives (two studies), a mixed population (one study), and one trial of patients with heart failure.

At follow-up, relative risks for all-cause mortality and cardiovascular mortality for both normotensives and hypertensives were only mildly to moderately reduced, and not to a statistically significant degree. In congestive heart failure patients, salt restriction actually significantly increased all-cause death.

Those are the inconvenient facts.  Now here’s how MacGregor and Feng He tried to fung foo all over them:

He and MacGregor, in their Comment, reanalyze the same data but combined the normotensives and hypertensives. They also omitted the heart-failure trial—a group of “very ill” patients taking large doses of diuretics in whom salt restrictions would seldom be recommended, MacGregor observed. In the combined patient analysis, they find a now statistically significant 20% reduction in cardiovascular events and a nonsignificant reduction in all-cause mortality.

Lovely.  If clinical trials don’t tell you what you want to hear, mix and match the data, toss out some data if need be, and presto! – you’ve got yourself a “significant” result … well, if you’re talking about cardiovascular events, that is.  If you’re talking about actual deaths, the results aren’t “significant.”

In layman’s terms, that means “the results are utterly @#$%ing worthless.”  But not to Action-Action Jackson MacGregor:

“We’ve done this reanalysis, and we’ve got the evidence. In fact, all the evidence about salt is overwhelming. . . . It all shows that salt is a major factor bringing up our blood pressure.”

All the evidence, really?  Like the clinical trials in which salt restriction changed blood pressure by a point or two at most?   Like the big, expensive clinical study the anti-salt troll insisted I read, in which adopting a diet with almost no salt at all caused blood pressure to drop by a whopping three points? (And that trial was conducted by researchers who wanted salt restriction to work.  They even tried to talk their way around the results in their conclusions.)

The only overwhelming evidence I see here is that some scientists are freakin’ liars.