Dear Mark: Salt and Blood Pressure
Mark’s Daily Apple
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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?
I went Primal
last year, and I'm down about 25 to 30 pounds and blood pressure
is lowered. I have definitely followed your advice on low salt.
For example, if I buy tomato sauce or paste, I get the "No Salt",
and I buy the low salt cashews, preferably with sea salt. What
do you think about this new research that has come out, saying
that salt is not that bad for you, and that it's not actually
related to heart disease? Just wanted your take.
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
Time to End the War on Salt." In fact, salt is kinda like the
Will it or won't it (kill you/clog your arteries/give you cancer/enter
nefarious-sounding characteristic of necessary dietary component
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:
the nervous system – both sodium and chloride (also known
as sodium chloride, or salt) are necessary for the firing of neurons.
blood pressure – keeps it from going too low or (usually)
maintain acid-base balance and blood volume.
the function of the adrenal glands which produce dozens
of vital hormones, including the stress
But how much
is too much? Is there such a thing as a limit to sodium intake?
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.
of evidence that the earliest humans were largely
coastal dwellers with a fondness for seafood – particularly
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.
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?
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.
the rest of the article
December 29, 2011
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