"Sodium and Arterial Function: A-salting our Endothelium"
If you put people on a low salt diet,
meaning only getting twice as much sodium as they need,
as opposed to a usual salt diet
where they’re getting five times more,
you get a significant improvement
in artery function.
Lower salt, better arterial function;
suggesting heart protective effects
beyond just blood pressure reduction.
Now this was after dropping people’s salt intake
by about a teaspoon a day for two weeks.
What if you only dropped salt intake
by like a half teaspoon a day?
You still get a significant improvement in artery function,
and it happens within just two days
of reducing one’s salt intake.
Or even after a single meal.
A high salt meal, which is to say
just a typical amount of salt consumed
in a commonly eaten meal,
can significantly suppress artery function
within 30 minutes.
Here’s what happens
30, 60, 90, 120 minutes after a meal
with just a pinch of salt in it.
Here’s what happens after the same meal,
but with a quarter teaspoon of salt in it.
A significant suppression of arterial function.
Now is this in addition to the spike
in blood pressure from salt
or because of the spike in blood pressure?
If you take people with normal blood pressure
and give them a bowl of soup
containing how much salt a regular meal might contain,
their blood pressure goes up
over the next three hours
compared to the same soup
with no added salt.
Now this doesn’t happen to everyone;
this is just the average response.
Some people are resistant to the effects
of salt on their blood pressure.
So, what if you repeated
the artery function experiment on them?
Unfortunately the title ruins the suspense and gives it away.
As you can see, even in people
whose blood pressure is unresponsive to salt intake,
they still suffer significant suppression
of their artery function.
So even independent of any effects on blood pressure,
salt hurts our arteries
and that harm begins within minutes
of it going into our mouth
for our major arteries
and even our itty bitty blood vessels.
Using something called laser Doppler flowmetry,
you can measure blood flow
in the tiny vessels in our skin.
Here’s blood flow at baseline.
Now to get the blood vessels to open up
they warmed up the skin.
The reason we may turn pink
when we get into a hot bath
is that the blood vessels in our skin are opening up.
And that’s what happens.
Big increase in blood flow with the warming.
But that’s on the low salt diet.
A high salt diet,
starts out the same at the beginning,
but after the same heating,
there’s significantly less blood flow.
The arteries just don't seem to open up as well
on a high salt diet, unless...
you inject vitamin C into their skin.
That seems to reverse the salt-induced
suppression of blood vessel function.
So if an antioxidant reverses the salt effect,
then the way salt may be damaging our artery function
is through oxidative stress,
the formation of free radicals in our blood stream.
But how?
There’s an enzyme in our body
that can detoxify a million free radicals per second,
24 hours a day, 7 days a week.
But compared to a low salt diet,
if we consume a normal salt diet,
we suppress the activity of this
detoxifying powerhouse of an enzyme.
That may be help explain why
“this is your artery function;
this, is your artery function on salt.”
With our antioxidant enzymes crippled by the salt
all the excess free radicals
may be crippling our arteries.
But mop up those extra free radicals up
by infusing vitamin C into the bloodstream,
and artery function returns to normal.
Whereas on a low salt diet,
if you drip vitamin C into people’s veins,
nothing happens,
because our antioxidant enzymes
are already taking care of business
and haven’t been shackled by the sodium
of a normal-salt diet.
Whereas potassium,
concentrated in fruits and vegetables,
soften the cells that line our arteries
and increase the release of nitric oxide
that allows our arteries to relax,
sodium in our blood stiffens the cells
lining our arteries within minutes,
and reduces nitric oxide release.
The more salt, the less nitric oxide is produced.
One salty meal, and not only does our blood pressure go up
but our arteries literally stiffen.
That’s why we could figure out
that too much salt was bad for us
4,000 years ago.
We don’t need a double blind trial,
maybe we don’t need to follow people out for a decade.
You may just have to feed someone
a bag of potato chips and take their pulse.