Dear Mark: Salt and Blood Pressureby
Mark Sisson Recently by Mark Sisson: Welcome Back Grok: 30 Days of Self-Discovery
The salt debate rages on outside these halls, but I've never really opened MDA's doors to the tempest (beyond a short dalliance several years ago). Today, though, I am. We've likely all consumed a fair bit of sodium chloride over the past holiday weekend, and I imagine a few of us are wondering whether that's a problem or not. Ever timely, reader John has written in with his salt story and a simple question: how much salt is suitable for humans? Here's his question:
There's a lot of back and forth on salt, even among mainstream researchers. It used to be that dietary salt was absolutely evil, that it would spike your (everyone's!) blood pressure and cause certain heart attacks and stroke. I mean, your average health-conscious grandparents probably still eat all their foods unsalted because, along with egg whites and 1% milk, that's just how you ate when you were trying to lower blood pressure and reduce the risk of an early death. But then stuff like the research to which John is most likely referring rolls around: this study (from the Cochrane Review in the American Journal of Hypertension) that Scientific American featured in its recent story, "It's Time to End the War on Salt." In fact, salt is kinda like the new egg. Will it or won't it (kill you/clog your arteries/give you cancer/enter nefarious-sounding characteristic of necessary dietary component here)? First of all, outright demonization of an element as important as sodium is silly and foolish. We literally have a physiological requirement for sodium (about 500 mg per day), and we come equipped with sensory apparati on our tongues (taste buds) specific to salt and extant for the express purpose of identifying salty things so we can consume them. It's obvious that salt is necessary, and that it's not poison. In fact, it:
But how much is too much? Is there such a thing as a limit to sodium intake? Loren Cordain thinks the amount of salt average Americans get daily – almost 10 grams, or 3,875 mg of sodium – is excessive and evolutionarily discordant as indicated by the earliest evidence of salt mining by homo sapiens coming from China in 6000 BC and Spain in 6200 BC, well after the advent of agriculture. In his paper, he acknowledges the likelihood that coastal dwellers "may have dipped their food in seawater or used dried seawater salt," but doesn't find that the totality of evidence supports high sodium intake by humans during the Paleolithic. While I agree with 10 daily grams of refined salt being evolutionarily discordant and possibly excessive for some people, I think he's overlooking something. There's plenty of evidence that the earliest humans were largely coastal dwellers with a fondness for seafood – particularly shellfish, which are rich in sodium. As I wrote in that shellfish post, basically any culture with coastal access left behind ample evidence of constant shellfish consumption. Some researchers are even suggesting that a bottleneck in human evolution occurred sometime between 190k and 130k years ago, when the total human population was reduced to about a thousand individuals living on the coasts of South Africa, eating a diet rich in seafood and especially shellfish. If it is from those thousand-odd humans that every current living human descends, and they were big shellfish eaters, I'd say it's pretty likely that we can tolerate a decent amount of salt.
According to the USDA database, three ounces of raw clams, oysters, and mussels provide 510 mg, 90 mg, and 243 mg of sodium, respectively. I even think they're undercounting the sodium content of oysters, personally. I regularly eat raw oysters on the half-shell, and there's no way that mouthful of briny goodness contains just 90 mg of sodium. I'm guessing they measured the oysters rinsed and cleaned and from a jar, rather than slurped straight out of the shell. If our direct ancestors (all of them, assuming this bottleneck occurred) ate steady amounts of salty seafood straight out of the shell/sea, then salt can't be bad, right? Kinda. Some people are genuinely "salt-sensitive." When they consume higher levels of salt, their blood pressure increases. When they drop the salt intake, their blood pressure drops with it. Studies indicate that of patients with hypertension, 51% are salt-sensitive (73% of African-American hypertensives are salt-sensitive), while 26% of normotensive patients are salt-sensitive. And since we know sodium chloride plays a physiological role in the regulation of blood pressure, this isn't controversial in the least. But the majority of randomized controlled trials have been inconclusive regarding the effects of salt on hypertension, as the Cochrane Review mentioned, and some studies have found a slight increase in disease from "low-salt" diets. Another found "normal sodium" diets resulted in better outcomes for congestive heart failure patients than "low sodium" diets (less followup hospitalizations and certain blood markers). The evidence is mixed and murky, for sure. December 29, 2011 Copyright © 2011 Mark's Daily Apple
|
