Sal / Sodium
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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 arterial 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 arterial 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 kind of ruins the suspense and gives it away, but 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 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 bloodstream. But how? Well, there’s an enzyme in our body that can detoxify a million free radicals a second, 24 hours a day, seven 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 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 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, softens the cells that line our arteries, and increases 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. Maybe we don’t need a double blind trial, maybe we don’t need to follow people for a decade; you may just have to feed someone a bag of potato chips, and take their pulse.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.
