When I returned from the Ancestral Health Symposium, I mentioned that one of the other speakers pooh-poohed a point I made in my speech about how sodium intake has little effect on blood pressure, then argued his point using bad science – which I found amusing, since my speech was about how to tell good science from bad science.
Here’s his speech. If you skip ahead to about the 9:00 mark, you’ll hear how Dr. O’Keefe “proves” that sodium does indeed cause hypertension.
Well, there you have it. The Yanomami Indians in South America have a low sodium intake compared to ours, and by gosh, you can’t find a single case of hypertension among ‘em. We’ve clearly established a link between A and B, so A must cause B. Case closed. See you next post.
No, wait … hang on a second … I hear some critical-thinking questions banging around in my head. Such as:
Q. Did the researchers control their variables?
You can’t see his slides in the video, but while Dr. O’Keefe was explaining how little sodium the Yanomami Indians consume, he was showing the audience pictures similar to these:
Hmmm … I wonder if sodium intake is the only difference between the lifestyle of the average American and lifestyle of the average Yanomami Indian? Based on these pictures, I’m guessing probably not. In fact, based on these pictures, I’m proposing a new hypothesis about hypertension:
Hypertension is caused by wearing pants.
If makes sense if you think about it. Your body is a bit like a big water balloon, and everyone knows if you squeeze a balloon, you increase the pressure inside. Now add in the fact that many Americans insist on wearing the same size clothes even as they get older and fatter, and you have a good explanation for why blood pressure tends to increase after middle age. I hereby propose we start prescribing nakedness as a cure for hypertension. (This will have the added benefit of speeding up security checks at airports.)
Pictures of the Yanomami have also inspired me to propose a second hypothesis:
You can prevent hypertension by poking holes in your skin and inserting bones.
I think this one is self-explanatory. If you think about that water-balloon example again, you’d have to agree that even if you increase the internal pressure by squeezing the balloon, you could offset the entire effect by poking a hole in the balloon’s skin.
The fact that these people consume less salt than we do and also have lower blood pressure than we do proves absolutely nothing. The lower blood pressure could be due to any number of factors.
Dr. Richard Johnson has presented some compelling evidence that hypertension is largely the result of consuming too much fructose, as I recounted in a previous post. Now, I must admit I’ve never visited the Yanomami tribes in person, but I’m willing to bet Dr. O’Keefe a thousand dollars that in addition to consuming far less sodium than we do, hunter-gatherers living in the Amazon jungle also consume far less fructose … unless they somehow manage to venture into the jungle and gather Krispy Kreme donuts, Frosted Mini-Wheats, Little Debbie Snack Cakes, Chunky Monkey ice cream, Heinz ketchup, fruit rollups, half-gallon jugs of Mott’s apple juice, and 44-ounce Coca-Cola Big Gulps.
Q. If we’re told A is linked to B, do we see that correlation consistently, or are there glaring exceptions in other populations?
A recent article published in Scientific American titled It’s Time to End the War on Salt reported on a meta-analysis of salt-restriction studies by the Cochrane Collaboration. Here’s what they found:
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, but, uh, you see … there’s this one tribe in South America that consumes very little salt, and they have low blood pressure, so that must prove salt causes hypertension. We’ll just forget about all those contradictions we find in other populations ….
Q. Is this an observational study or a clinical study?
Dr. O’Keefe’s observation is just that – an observation. So what do the clinical trials tell us about salt intake and blood pressure?
Hypertension is defined as blood pressure that’s more than 20 points above normal. If salt causes hypertension, then drastically restricting salt intake – all by itself – should produce a drop in blood pressure of 20 points or so. But that simply isn’t the case. In the section of my speech that Dr. O’Keefe didn’t like, I recounted the results of a large clinical study in which researchers had the study subjects reduce their salt intake by 75%. That led to a whopping three-point drop in blood pressure on average.
Other clinical studies have produced similar (or even less-impressive) results. Here’s more from the Scientific American article:
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. The review concluded that “intensive interventions, unsuited to primary care or population prevention programs, provide only minimal reductions in blood pressure during long-term trials.” A 2003 Cochrane review of 57 shorter-term trials similarly concluded that “there is little evidence for long-term benefit from reducing salt intake.”
Since my blood pressure has always been normal or a little on the low side, I believe I’ll keep putting salt on my food, Dr. O’Keefe. But if it makes you feel any better, I’ll spend more time not wearing any pants.